WO1984000554A1

WO1984000554A1 - Moldable material containing a fibrous product in the form of bidimensional or tridimensional microfibers

Info

Publication number: WO1984000554A1
Application number: PCT/DE1983/000135
Authority: WO
Inventors: Otto Kopp; Helmut Holzer
Original assignee: Sued West Chemie Gmbh
Priority date: 1982-08-03
Filing date: 1983-08-03
Publication date: 1984-02-16
Also published as: DE3228989C2; DK140184D0; DE3228989A1; DK140184A; EP0126083A1

Abstract

The moldable material contains a fibrous product in the form of bidimensional or tridimensional granular and flowing microfibers as well as a binder, particularly for the injection molding of form parts. The microfibers have a maximum thickness of 0.02 mm and a maximum length of 1.0 mm, and the fibrous product has a maximum diameter of 0.5 mm. The moldable material improves the physical characteristics of form parts such as the tensile strength, alternate elongation, bending strength, resilience, heat stability of the form, shrinking resistance, thermal conductibility and electric insulation.

Description

Molding fibers containing microfibers in the form of two- or three-dimensional fiber structures

The invention relates to granular, free-flowing, microfibers in the form of two- or three-dimensional fiber structures and to molding compositions containing binders, which are particularly suitable for injection molding of molded parts. In addition, the invention relates to a method for producing such molding compositions and to their use.

Such molding compositions frequently contain so-called “thermosets” or precursors thereof as binders, which, after they have completely hardened (usually in a hot form), are closely meshed, cross-linked, highly polymeric materials.

In chemical terms, the molding compositions are mainly based on phenolic resins, urea resins, melamine resins, melamine-phenolic resins, polyester resins, epoxy resins and diallyl phthalate.

The importance of thermosetting molding compounds is reflected e.g. in their total consumption in Western Europe of about 325,000 tons in 1978 again. The molded parts produced therefrom are widely used in the fields of the electrical industry, motor vehicle construction, aircraft construction, shipbuilding, rocket technology, chemical industry, office machines and household appliances.

Due to the increasing costs for capital goods worldwide, there is great interest in various types of molded parts with a very long service life. In addition, for special applications, for example in rocket technology, materials are required which have to withstand extreme mechanical, thermal and electrical loads. Such molded parts can with the moldable ^' n not be produced.

In addition, the aim is to simplify the listening position of molded parts from molding compounds as much as possible and to carry them out in a safer and more environmentally friendly manner. The use of a molding compound in the form of a free-flowing granulate is particularly suitable for this purpose, since this product form can be easily transported and metered within a processing device and, by avoiding dust, eliminates material losses and imposes a burden on the environment and personnel.

The use of microfibers with a diameter of 0.002 to 0.015 mm and a minimum length of 0.4 mm in connection with a reinforcing resin, e.g. a phenol-formaldehyde resin has been reported (see European Patent Publication No. 0 047 701). These fibers are intended for the production of a material which protects against heat, a substrate consisting of the fibers being immersed in a solution of the said resin. So this is not a molding compound and a molded part made from it in the usual sense.

In the publication "VDI-Nachrichten" NR. 12, March 19, 1982, fiber-reinforced plastics based on phenolic and epoxy resins are mentioned. Carbon fibers are incorporated into these materials for highly stressed molded parts. The thickness of such a fiber is approximately 0.01 mm. Nothing is said in this document about the shape of the fibers. - -

From AT 347 692 a die casting process for producing a cast resin reaction resin containing fibers as a filler is known. Spiral, corrugated or crimped and / or fibers formed into balls are mixed into the reaction resin as filler. The fibers have a length of 2 to 20 mm. The publication expressly emphasizes that shorter fibers do not improve the strength properties.

The invention is based on the object of specifying granulated, free-flowing, microfibers in the form of two- or three-dimensional fiber structures and molding compositions containing binders, in particular for injection molding, from which molded parts can be produced, the physical properties of which in relation to the special purpose of the respective molded part are improved compared to known molded parts. Examples of such physical properties are tensile strength, elongation at break, flexural strength, impact resistance, dimensional stability under heat, shrink resistance, thermal conductivity and electrical insulation.

Which of the physical properties is to be improved depends on the particular type of use of the molded parts to be produced from the molding compositions.

In addition, it should be possible to use inexpensive resins for the molding compositions and still achieve such advantageous physical properties of the compositions as are otherwise only possible with expensive resins. The aforementioned object is achieved in that the microfibers have a maximum thickness of 0.02 mm and a maximum length of 1.0 mm and the fiber structures have a maximum diameter of 0.5 mm.

Molding parts can be produced from the molding compositions according to the invention which, in particular with regard to their mechanical properties, e.g. in the case of tensile, compressive, bending, impact or vibration loading, known molded parts which do not contain these special microfiber structures are superior.

The fiber structures have a diameter of at most 0.5 mm, preferably 0.1 mm.

If this maximum size is observed, a statistical, that is to say unoriented, distribution of the fiber structures, as is usually desired, is retained even when the molding composition is injection molded.

If the fiber diameter e.g. Is 0.01 mm, the preferred maximum size of the fiber structures corresponds to fifty times this fiber diameter. But even at twenty or thirty times this diameter, satisfactory results are still achieved,

If the fiber structures have a diameter of more than 0.5 mm, they can be deformed when the molding compound is injected into a mold. In this case, the optimal mechanical properties of the hardened molded parts are not achieved.

The cross section of the microfibers can be very different, for example approximately circular, elliptical, oval, triangular or quadrangular or polygonal or irregular. Hollow fibers may also be considered, which may have a longitudinal slot. _ 3 _

The microfiber can be arranged relatively regularly or very irregularly within a ball. Twisting of the individual fibers is also possible.

Depending on the shape of the fiber cross-section, the cross-sectional circumference is of different lengths or the adhesive surface of the microfiber available for the contact between the binder of the molding composition and the microfiber is of different sizes. In general, microfibers are all the more preferred the longer the cross-sectional circumference or the larger the mentioned adhesive surface.

With regard to their chemical nature, very different inorganic and organic microfibers come into question.

Inorganic fibers are e.g. Mineral fibers made of asbestos or calcium aluminum silicate, glass fibers or fibers made of carbon, such as graphite, or silicon carbide, silicon nitride, silicon dioxide, silica, zirconium oxide, zirconium silicate, boron, boron nitride, boron carbide, aluminum oxide or metals, such as steel, aluminum, magnesium, molybdenum or tungsten.

Examples of organic fibers are natural fibers made of sisal, jute, hemp, henecen, cellulose fibers or palm fibers, and synthetic fibers such as fibers made of polyester, polyacrylonitrile, polypropylene, polyamide and aramid (polyamide with a high aromatic content).

Mixtures of fibers of the aforementioned type can also be used, which is usually preferred. The granules in which the molding compositions are present have a customary grain size. The grain size is preferably approximately 2.5 mm.

According to a preferred embodiment of the invention, the microfibers are largely individually present in the molding compositions, largely avoiding fiber bundles. This has the advantage that each individual microfiber contributes to the reinforcement of the molding composition or of the molded part produced therefrom, with fewer microfibers being sufficient for a given degree of reinforcement than in the case in which fiber bundles are present, in which a large part the microfibers are ineffective. The avoidance of fiber bundles leads also to reduce the cost of molding materials, as less microfibers are required if each one of them ^* contributes to improving the mechanical properties of the final cured product.

According to a further development of the invention, the microfibers have a length which corresponds approximately to fifty times the fiber thickness. On the one hand, this length brings with it a sufficiently large adhesive surface with respect to the binder of the molding composition for each microfiber and is also sufficient for the formation of the desired fiber structure. On the other hand, this length is not so great that when the molding compound is processed into molded parts, e.g. in injection molding, in the flow of the liquefied molding compound, the microfibers are mostly undesirably aligned.

It has also proven to be very advantageous if the adhesive surface of the microfiber available for the contact between the binder of the molding composition and a microfiber is generally more than that

Hundred times the cross-sectional area of the microfiber is. As the size of the adhesive surface of the individual microfibers increases, a force that is exerted on the molded part containing the microfibers is better transmitted to the microfibers, the cured binder in the molded part being relieved at the same time. Overall, this leads to more favorable mechanical properties of the molded part.

The aforementioned ratio of the adhesive surface to the cross-sectional area of the microfiber can also be regarded as a measure of the length of the microfiber. The stated minimum size of the adhesive surface, expressed as a hundred times the cross-sectional area, results for microfibers with an essentially circular cross-section. With the same fiber length, but a fiber cross-section with a larger cross-sectional circumference (for example with longitudinally slotted hollow fibers or fibers with a cross-section in the form of a flat rectangle), the stated ratio of adhesive surface to cross-sectional area can be approximately 150 to 230, in special cases even over 250. Microfibers with such large adhesive surfaces are particularly cheap.

The volume ratio of the molding compound binder (matrix) and the microfibers can be very different. In the case of fiber structures in the form of helices with about two and a half courses, the ratio of the two volumes (matrix: microfiber) can e.g. about 3.2 (if the helix diameter corresponds to approximately five times the fiber diameter) to approximately 12.7 (if the helix diameter corresponds to ten times the fiber diameter). This volume ratio can, however, also assume values outside the range mentioned for other coils. This depends on the number of turns of the helix and their mutual distance, for which there is a large scope within the scope of the invention. -

It is advantageous if the material of the microfibers has a greater modulus of elasticity than the binder of the respective molding compound. An important reason for the use of fibers in molding compositions is that, when mechanical forces act on the hardened molded part, the reinforcing fiber should relieve the surrounding resin matrix as much as possible, that is to say it should absorb as much tension as possible with as little deformation as possible. This is best achieved in that the fiber has a higher modulus of elasticity than the resin matrix to be reinforced. At the same time the self-evident prerequisite must be met that the adhesion

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between the fiber and the resin matrix is very good; this places a mechanical load on the molded part on both components, i.e. on the resin matrix and the

Fibers, distributed.

The binders of the molding compositions preferably consist of 10 to 50 percent by weight of microfibers. If less than 30 weight percent microfibers are used, only a slight reinforcing effect is achieved. The use of more than 50 percent by weight of microfibers leads to a noticeable increase in the cost of the molding compositions because of the relatively high cost of the microfibers, without a corresponding improvement in quality being achieved.

The molding compositions contain, as a binder or resin matrix, in which the microfibers are distributed, preferably a precondensed, prepolymerized or pre-added organic resin. Such resins have the advantage that, depending on the molding process to which the molding compositions are subjected, they can be adjusted with regard to the extent of the pre-crosslinking. With these deformation processes, e.g. in injection molding, the crosslinking of the molding compound to the cured molded part is completed, i.e. Depending on the type of crosslinking reaction, the polycondensation, polymerization or polyaddition of the organic resin is completed.

In addition to the above-mentioned molding compound components, the binder or the resin matrix and the microfibers, the molding compounds can also contain other conventional constituents. These include e.g. Fillers or other auxiliary substances, e.g. can be liquid, powdery, granular, fibrous, carved or cord-like. Specific examples of this are wood flour, wood fibers, rock flour, such as chalk, kaolin, mica, talc and asbestos flour, asbestos

OMPI fibers. Asbestos cords, lubricants, fluxes, dyes, color pigments and curing catalysts.

In particular, in addition to the microfibers, the molding compositions may also contain macrofibers which are already customary in molding compositions and whose dimensions exceed those of the microfibers.

The microfibers used according to the invention can also be pretreated in a customary manner in order to increase the adhesion to the molding compound binder. Suitable adhesion promoters are known (e.g. from "GLASS TECHNICAL REPORTS, JOURNAL FOR GLASS CUSTOMERS", Volume 37 (1964), No. 1, pages 1 to 15). It is e.g. around silanes or organic chromium complexes. The coupling agent is normally applied to the fibers, e.g. Glass fibers, applied directly during fiber production in the form of a so-called "size" or as part of a final treatment of the fibers.

There are ^"adhesion promoters that are not applied to the fibers, but be reasonably added as a mixture component the shape-.

The molding compositions can drive are manufactured according to the inventive Ver _¬, which is characterized in that interferes during the production of the respective molding material underlying the binder or the resin matrix microfibers in the binder or the resin _¬ matrix or thereof in a preliminary stage. These

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The procedure has the advantage that the microfibers can be incorporated if the binder or resin on which the molding composition is based has a relatively low viscosity, which permits a uniform distribution of the fiber structures without substantial deformation.

The incorporation of the microfibers at low viscosity not only promotes good wetting of the fibers with the resin and thus increased adhesion between the two, but also facilitates the uniform distribution of the microfibers in the molding composition while avoiding localized fiber accumulations.

For example, the microfibers can be added during the condensation reaction of a phenolic resin in a process stage in which the viscosity of the resin is not yet too high. On the other hand, the viscosity should not be too low to avoid segregation of the resin-microfiber system.

However, it is not absolutely necessary to mix in the microfibers during the production of the respective binder. This mixing can also take place in a later process step in the production of molding compositions. However, it is expedient if the microfibers are incorporated into the molding compositions before other reinforcement

OMPI Components, for example macro fibers, are supplied to the molding composition. In this sense, the molding compositions according to the invention can also be regarded as an improved preliminary stage for the production of the final molding composition which also contains further reinforcing agents, as mentioned above in connection with the additives.

Mixing the microfibers into the binder or

Resin of the molding compound can be made, for example, by means of a roller mill with a gap width of approximately 0.5 mm or less. The microfibers can also, for. B. in a ^S the low viscosity resin trom be introduced.

According to the invention, the aforementioned molding compositions are used for the production of molded parts. The production processes include, for example the customary processes for processing molding compositions, such as injection molding, injection molding and simple pressing, into consideration.

The most important processing method for the molding compositions described here is injection molding. The advantage of using microfibers is particularly evident here, since the small dimensions of these fibers or the fiber structures ensure that the original fiber structure is maintained. A deformation and / or alignment of the fiber structures with the consequence of non-optimal physical properties of the hardened molded parts is thus avoided.

When they are finally processed, the molding compositions are fed as granules to an injection molding device, melted there and at a temperature of about 150 ° C.-190 ° C. injected into a hot mold under pressure. This supply of heat completes the crosslinking that has already taken place to a certain extent in the molding composition, the desired cured one

Molding is formed. The hardened molding compound then represents a thermosetting material which can no longer be liquefied by renewed heating, but decomposes when there is a strong supply of heat.

Claims

Patent claims

1. Granulated, free-flowing, microfibers in the form of two- or three-dimensional fiber structures and molding compositions containing binders, in particular for injection molding of moldings, characterized in that the microfibers have a maximum thickness of 0.02 mm and a maximum length of 1.0 mm and the fiber structures have a maximum diameter of 0.5 mm.

2. Molding compositions according to claim 1, characterized gekennzeich¬ net that the microfibers are largely present individually, largely avoiding fiber bundles.

3. Molding compositions according to one of the preceding claims, characterized in that the microfiber length corresponds approximately to fifty times the microfiber thickness.

4. Molding compositions according to one of the preceding claims, characterized in that the adhesive surface of the microfiber available for the contact between the binder of the molding composition and a microfiber is generally more than a hundred times the cross-sectional area of the microfiber.

5. Molding compositions according to one of the preceding claims, characterized in that the microfiber material has a greater modulus of elasticity than the binder.

6. Molding compositions according to one of the preceding claims, characterized in that the binder consists of 10 to 50 percent by weight of microfibers.

7. Molding compositions according to one of the preceding claims, characterized in that they contain a pre-condensed, pre-polymerized or pre-added, organic resin as a binder in which the microfibers are distributed.

8. The method for producing the ^* mentioned in claims 1 to 7 molding compositions, characterized gekennzeich¬ net, that one of its precursors interferes Mikro¬ fibers during manufacture of the means of Bindemit¬ in this or.

9. Use of the molding compositions according to one of claims 1 to 7 for the production, in particular for injection molding, of molded parts.