WO1995000584A1 - Plastifiable asbestos-free phenolic-resin moulding compound based on resol resin - Google Patents

Abstract

Proposed is a moulding compound, in particular a moulding compound for use in the manufacture of commutators for electric motors and dynamos, containing a phenolic resin or a mixture of phenolic resins plus added fillers and glass fibres. The invention calls for the moulding compound to contain 20 to 50 % by wt. of fillers and about 30 % wt. of glass fibres. By virtue of this composition and the fact that it is prepared in a fluid mixer, a finely particulate but dust-free granular intermediate product is obtained for further processing. To prepare the moulding compound, the raw materials are placed in a turbomixer and a mixture consisting of 20 to 30 % by wt. of resol resin plus 1 to 6 % by wt. of cashew-nut oil resin is added.

Description

Plasticizable asbestos-free phenolic resin molding compound based on resol resin

State of the art

The invention relates to glass fiber reinforced phenolic resin molding compositions, in particular for collectors and commutators of electric motors in accordance with the preamble of the main claim.

For the manufacture of commutators of starter motors, DE 38 38 106 discloses glass fiber reinforced molding compounds with phenolic resins and a filler content of 5 to 10 percent by weight of mica particles which have a non-porous, heat crack resistant molding compound. Harmful asbestos fibers as fillers were avoided. The mica content can be set as the only parameter for setting the property profile of the molding composition.

Conventional molding compositions which contain resols dissolved in water are sticky and bake during prolonged storage even if the molding compositions are mechanically stabilized or reinforced by fibers and fabrics. These resole resin molding compounds cannot be plasticized. The proportion of phenolic resin, especially novolak and resol, is usually 30-50 percent by weight of the total mass the molding compound. A typical example is described by A. Knop and LA Pilato, Phenolic Resins, Springer Verlag, Berlin, 1985, page 136. Phenolic resin molding compositions are maintained on heated roller mills or prepared for use with extruders or kneaders. The molding compound is obtained in patties which are ground. Grains of dust with an amount of up to 15 percent by weight of the molding composition inevitably form as undesirable by-products, which means that filters have to be used, which have to be changed frequently. A disadvantage of the preparation in the fluid mixer is that with high filler proportions of the molding material that no granules but woolly products, with low filler proportions that undefined conglomerates are formed as products.

Advantages of the invention

The molding compositions according to the invention have the following advantages:

- Asbestos-free molding compounds

- Plasticization of the molding compounds

- for a short time, up to 400 degrees Celsius, temperature-resistant molding compound

- satisfactory adhesion to metals, especially copper

- no cause of metal corrosion

- fine-grained, dust-free granules for processing

- Very good insulating properties, thermal shock resistance and sensitivity to moisture.

In addition, the following requirements must be met for the process for producing the molding compositions:

- Production in the fluid mixer

- Reproducible impregnation of fibers and fillers, i.e. homogeneous product

- Coordination of mechanical stability through fiber, mineral filler and / or fabric masses. The object of the invention is to produce a plasticizable, asbestos-free molding compound based on phenolic resins, especially liquid resole resins and resole resin with cashew nut oil resin and resole resin with novolak resins in a fluid mixer, which fulfill the above-mentioned property profile for the production of collectors for electric motors.

The preparation of the molding composition in accordance with the recipes of the invention in a fluid mixer provides granules with a narrow particle size distribution without oversize with good plasticizability. Resol resin-based phenoplasts of this type have a limited shelf life, but have very advantageous adhesion properties compared to known metals and metal alloys. Good adhesion to copper components, such as collectors of electric motors, is achieved with good moldability in the manufacturing process. The molding compounds are well absorbed in the plasticizer and do not splice during extrusion, which results in a homogeneously compacted preform.

The production of fine-grained molding compound granules, which have no dust particles, reduces the manufacturing effort and processing effort by saving dust filtering and breathing protection. In addition, the grinding process is omitted. Avoiding asbestos takes into account the legal ban on asbestos and the avoidance of carcinogenic substances.

The measures and procedural details listed in the subclaims enable improvements to be achieved compared to the general features given in the main claim. It is possible to achieve homogeneous mixing and reliable impregnation of the molding composition, in particular of its fibers, during the production of the molding composition. The mechanical stability can be adjust the ratio of the long-fiber to the short-fiber portions as well as the type and amount of mineral fillers and the respective proportions of all of these substances in the total mass of the molding composition. The very short mixing times correspond to the requirements of modern, automated production and enable the production of an advantageously granulated, fine-grained molding compound which can be plasticized and pressed and which supplies preliminary products, for example tablets, as a starting basis for the production of electrical engineering end products.

embodiments

Suitable resol resins and novolak resins are commercially available. The mass ratio of the resin components for resol resin: cashew nut oil resin, resol resin: novolak resin can be varied within limits. The proportion of the resin component, or a corresponding mixture of the phenolic resin components, in the total mass of the molding composition is a minimum of 20 to a maximum of 35 percent by weight.

Advantageously used release agents are stearates, in particular zinc and calcium stearate, their mixtures or chemically related stearates in a proportion of 0.3 to 3.5 percent by weight based on the total mass of the molding composition.

Oxide of divalent cations, in particular the alkaline earth oxides MgO, CaO, SrO, BaO with a proportion of 0.1 to 0.5 percent by weight, based on the total mass of the molding composition, are suitable as accelerators.

For glass fibers, fiber lengths according to Tables 1 and 2 given below were used. The glass fibers are commercially available from conventional silicate glass, in particular E-glass in various fiber lengths of, for example, 3, 4.5, 6, 12 and 30 millimeters available. Short glass fibers are obtained by suitable shredding, for example by grinding the glass fibers under defined, reproducible grinding conditions. Glass fibers with a fiber length of 4.5 millimeters and short fibers with a fiber length of predominantly 0.2 millimeters for commutators of starter motors of starters for motor vehicles were particularly suitable as long fibers. With a mass ratio of long fibers: short fibers = 2: 1, this selection of the glass fiber lengths proved to be particularly advantageous for the desired property profile and manufacturing process. It was also possible to obtain molding compositions with the desired property profile by means of short glass fibers, for example predominantly 0.5 millimeter fiber length. In isolated cases, it has proven to be advantageous to replace the glass fibers with polyacrylonitrile fibers or mixtures of glass fibers and polyacrylonitrile fibers. The proportion of fibers in the total mass of the molding composition is preferably 20 to 35 percent by weight and a mass ratio of short fibers: long fibers of 4: 1 to 1: 0.

Chalk, leaf silicates, mica, wollastonite and aluminum hydroxide with 20 to 40 percent by weight of the total mass of the molding composition were used as fillers. Aluminum oxide, rare earth oxides and mixtures thereof are also conceivable as fillers. A mixture of 13 percent by weight of chalk and 20 percent by weight of leaf silicate fulfilled the property profile very well. A mixture of 10 percent by weight of leaf silicate and 20 percent by weight of chalk made it possible to produce a granular product very well. In addition, wood flour, cellulose, textile fibers, textile fabrics, veneer chips can be used as fillers.

If desired, the molding composition can also be colored by incorporating a coloring inorganic or organic substance as a pigment, color paste or solution. The coloring matter is appropriate, added gege _¬ in amounts between 0.1 to 2.5 percent Gewichts¬, based on the sum of the components of Formmassse lie. By further processing the molding composition at 60 to 80 degrees Celsius, it is possible to plasticize the molding composition from the granules, which are at most pea-sized, into tablets or strands. Pressing the tablets or strands in automatic production systems is problem-free.

It is also possible to replace phenol with modified phenols such as cresols or thermoplastic modified phenols in whole or in part and to use them in the form of mixtures in combination with resol resins. It is also conceivable to partially replace cashew nut oil resin with related substances. It is also possible to mix glass fibers with more than two different fiber lengths.

The preparation process is carried out in a cylindrical container of a fluid mixer, in particular a heating / cooling mixer of open construction. The release agent, the accelerator, the glass fibers, the fillers, and possibly the dye are weighed in the mixer and mixed. Resole resin with up to 6% by weight cashew nut oil resin or resol resin with novolak resin are added with stirring. Cashew nut oil is described in "Römpp Chemie¬ lexikon", Volume 1, 8th edition, 1985, page 614. The mixing material introduced is mixed by the rotating, ring-shaped or wing-shaped tools of the mixer, thrown against the wall as a result of the centrifugal forces and pushed up. It leaves the influence of the rotors and returns to the bottom of the container under the influence of gravity in the middle of the container. Due to the high relative speeds of the individual mixed material particles, intense heating and thus condensation occurs as a result of the friction. The temperature of the mix is kept at 120 degrees Celsius, which is usually achieved by cooling the container. The power consumption of the stirrer is recorded to record the change in the viscous properties of the mix. The Resin impregnates the fillers with a sufficient mixing time, which is usually between 2 and 15 minutes, so that a homogeneous molding compound is obtained. The energy consumption of the mixer changes due to a change in the viscous properties of the mix. If the required degree of condensation is reached, this is indicated by a threshold value of the stirrer output.

The molding compound is drained into the cooling mixer in order to stop further condensation of the molding compound. A homogeneous, fine-grained granulate is obtained which, in contrast to ground molding compositions according to the prior art, has only a few dust particles. The absence of dust is checked by a sieve test of the molding compound. The mass of oversize can also be determined and, if necessary, eliminated in a further process step. The average grain diameter of the intermediate granules is 1 to 5 millimeters. A grain size of 0.7 millimeters or smaller is defined as dust that is screened out. The molding composition contains a maximum of up to 5 percent by weight, preferably less than 3 percent by weight, of dust. These molding compounds are very free-flowing.

As an alternative to the above further treatment, a molding compound which corresponds to the material composition of the invention can also be prepared using roller mills or kneaders, although the grinding and the dust which results from this must be accepted.

8th -

Examples of the material selection of phenoplasts with the advantages of the invention are listed in Tables 1 and 2. The figures relate to percentages by weight based on 100 percent by weight of molding composition.

Table 1

Examples

Molding compound 1 2 3

Resin Resol Resol Resol

22 22 27 Novolak Novolak Cashew Nut Oil 6 3 1

Release agent calcium stearate calcium stearate calcium stearate 2.5 2.5 2.5

Accelerator CaO CaO CaO 0.5 0.5 0.5 short glass fibers E-glass E-glass E-glass 20 17 24 long glass fibers E-glass E-glass E-glass 10 17 6

Filler Al hydroxide chalk chalk

20 14 25 leaf silicate leaf silicate leaf silicate

17 24 14

Carbon black dye ^- 2 ^"

Total mass 100 100 100 - 9 -

Table 2

Examples

Molding compound 4 5 6

Resol Resol Resol

Resins 22 22 27 Cashew nut oil Cashew nut oil Cashew nut oil 6 6 6

Release agent zinc stearate zinc stearate zinc stearate

1 4 2.5

Accelerator MgO MgO MgO

0.1 0.5 0.5 short glass fibers E-glass E-glass E-glass 30 10 30 long glass fibers E-glass

- 20 -

Filler chalk leaf silicate Al hydroxide

15 35.5 17.5 leaf silicate leaf silicate

25.9 16.5

Dye pigment

- 2 -

Total mass 100 100 100

Claims

Expectations 1. Molding composition, in particular for the production of collectors for electrical machines, with phenolic resin or mixtures of phenolic resins and admixtures of fillers and optionally glass fibers, characterized in that 20 to 60, preferably 20 to 40 percent by weight of the molding composition are fillers and that 0.1 to 6 percent by weight of the molding compound is cashew nut oil resin. 2. Molding composition according to claim 1, characterized in that the component of phenolic resins or mixtures of phenolic resins is resole resin and resin based on cashew nut oil or a mixture of resole resin and novolak resin. 3. Molding composition according to claim 1, characterized in that short and long-fiber glass fibers are in the molding composition and the mixed mass ratio of short-fiber glass fibers to long-fiber glass fibers is 4: 1 to 1: 0. 4. Molding composition according to claim 3, characterized in that the Glas¬ fiber length of the long fibers used 1 to 10 mm, preferably 4.5 millimeters, the fiber length of the short fibers used 0.1 - 1 mm, preferably 0.2 - 0.5 millimeters is. 5. Molding composition according to claim 1, characterized in that the Füll¬ materials asbestos-free mineral fillers, in particular silicates, aluminum hydroxide, rock flour and preferably chalk or mixtures of these materials and / or additionally contain wood flour, cellulose, textile fibers, textile fabrics and veneer chips. 6. Molding composition according to claim 1, characterized in that the molding composition contains accelerators and release agents and / or dyes. 7. A process for producing a molding composition according to one of claims 1 to 6, characterized in that the metered constituents of the molding composition are introduced together in a fluid mixer, mixed intimately and the mixture is kept at 120 degrees Celsius and stirred until the required degree of precondensation is achieved. 8. The method for producing a molding composition according to claim 7, characterized in that during the mixing of the metered components of the molding composition as the last component of the mixture, a mixture of resol resin, novolak resin and resin based on cashew nut oil or a mixture of resol - And novolak resin is added. 9. A method for producing a molding composition according to one of claims 7 or 8, characterized in that after the required degree of condensation has been reached, the mixture is transferred to a cooled container or to a cooling belt. 10. A method for producing a molding composition according to claim 9, characterized in that the mixture is processed after a pre-plastification. 11. A method for producing a molding composition according to one of claims 7 or 8, characterized in that the mixture is processed with roller mills or kneaders.