EP2595780B1 - Composite material for further processing into sheet-like abrasive products and process for the production thereof - Google Patents

Description

The present invention relates to a composite material which is suitable as a precursor ("abrasive carrier") for the production of flat, usually relatively stiff, but still elastically deformable abrasives such as grinding wheels or the like.

Flat grinding wheels are still produced today by first impregnating a vulcanized fiber mat with an organic binder, which is then dried. This product is sprinkled with the abrasive manufacturer with abrasive grains which are made to adhere to the substrate with another layer of the same or a different binder. The material thus obtained is dried, cured and cut into the desired shape.

The production of vulcanized fiber has been known for a long time. The raw material used is cotton and / or cellulose fibers. These are processed into paper webs, which then pass through a parchment bath, wherein the surface of the individual fibers is dissolved; on the surface of which so-called hydrate cellulose is formed. This causes an intimate bonding of the fibers with each other.

Today, two different methods are used in practice. The former is the zinc chloride process. The preparation is carried out by impregnation with nearly saturated, 75 ° C hot zinc chloride solution, which, however, can lead to accumulation of zinc in the material. The sulfuric acid process is just as important industrially. Here, the paper pulp is abgegautscht (the liquid is pressed), whereby the individual fibers are interconnected and, if necessary, individual paper webs together. Without the addition of further binders, a nearly homogeneous mass of fibers surrounded by hydrate cellulose is produced.

Both methods require large amounts of water. The treatment agents used zinc chloride or sulfuric acid are highly polluting.

The fiber quality and the setting of the parchment determine the quality of the vulcanized fiber.

With the necessary experience, the variation possibilities can be used to produce vulcanized fiber of the most varied quality and thus to adjust their properties to specific fields of application.

There are a number of suggestions as to which binder (s) the vulcanized fiber material can be coated to obtain an abrasive backing. Sun strikes DE 28 53 761 at least that the primer layer should consist of a resol from a monohydric phenol and formaldehyde in specific proportions.

DE 103 04 958 A1 suggests the use of an aqueous polymer dispersion of dispersed polymer particles of at least one first polymer having a glass transition temperature prepared by free radical emulsion polymerization in the presence of a second polymer of at least one ethylenically unsaturated mono- and / or dicarboxylic acid and at least one specifically defined ethylenically unsaturated ester , With this polymer dispersion papers, fabrics or other bodies suitable for grinding can be coated. Paper, tissue, foil or vulcanized fiber may be used according to EP 1 141 125 B1 be used as an abrasive carrier; as a coating composition therefor, a combination of a specific oligomeric aminoplast resin and a thermoplastic polyamide is proposed.

A disadvantage of the use of vulcanized fiber as a base material for grinding wheels or the like. Is the high water absorption capacity of over 8%, which is particularly caused by the high alkali content. Due to the water absorption, the disc curls. In addition, the discs tend to embrittle.

DE AS 29 28 484 describes the production of flexible abrasives using a polyester-containing base fabric with an amine-formaldehyde resin. From this it can be seen which problems with regard to stiffness, flexibility and extensibility the expert has to face when he wants to use a fabric as a carrier. In particular, it is found that it is disadvantageous to coat such fabrics with binders of phenolic resins based on resorcinol or resorcinol-formaldehyde. Another polyester fabric as a base for abrasive cloth is in DE OS 25 31 642 disclosed.

Resin-bonded molded articles, which may be suitable, inter alia, as grinding wheels, also discloses DE 102 30 573 A1 , For their production, a fabric insert is impregnated with a thermosetting binder, which is added to the binder, a fatty acid to avoid sticking and thus for proper separation of the stacked fabric inserts.

In DE OS 26 59 029 discloses a method of making abrasive paper or abrasive cloth. Thus, the abrasive grain is applied and fixed by means of a slurry containing a urea-formaldehyde precondensate, a liquid phenolic resin, and the abrasive grain. However, it has been found that applying and fixing the abrasive grain in the form of such a slurry directly onto a (possibly bonded) nonwoven fabric does not result in a product having the required stability. This must be large enough to withstand the centrifugal force with a fast rotation of the grinding wheel.

Fabrics are typically used for so-called "flap disks" or "flap-disk" applications (laminated "abrasive mops") and not for flat grinding wheels.

In US 5,830,248 the production of an abrasive endless belt is described. For this purpose, a carrier is provided with reinforcing fibers, these fibers individually or as filaments first soaked with a resin solution and then wound on a drum on which the carrier is parallel to each other. The reinforcing material is solidified with a binder; it is emphasized that the binder precursor should not flow to solidify the reinforcing fibers during the curing process to later minimize the mobility of the abrasive particles during the application of the abrasive coating. The binder is therefore cured before the abrasive layer is produced.

An entirely different class of abrasives are elastic shaped bodies, as they are known in households under the name "Scotch Brite". Such a shaped body is for example in US 2008/0127572 A1 described.

Specific friction discs are needed in the auto industry. The organic binders used contain according to DE 10 2007 053 498 A1 For example, phenolic resins and are finally carbonized together with the other components.

Fabrics are used for the production of endless abrasive belts, see eg WO 2005/110681 A1 or EP 1 113 903 B1 , Alternatively suggests US 5,681,612 a method in which a fibrous material is pressed against the outer wall of a drum, which is then solidified by introducing a binder precursor and rotating the drum by means of centrifugal forces to form an endless belt.

However, the load on endless abrasive belts is completely different than that of grinding wheels. Tissues are usually unsuitable for eg round grinding wheels, as already mentioned above. Therefore, in practice, such grinding wheels are not even encountered. Their extensibility would namely obliquely to the thread direction substantially greater than in the warp and weft direction. Depending on the fabric used, however, these directions would also have different extensibilities when working with different warp and weft threads. It should therefore be expected by those skilled in the art that such carrier materials would result in "bleeding" and corrugations in the grinding wheel. To achieve a sufficient internal strength also an extremely high thread density in the tissue would be necessary, which would be a cost-driving factor. Well out For this reason, in practice, volcanic fiber materials are still substantially selected for the substrate of grinding wheels in practice.

The object of the invention is to enable the production of an abrasive material which is suitable as a means for abrading flat or shaped surfaces, in particular in the form of (for example round) grinding wheels. This should preferably be able to be manufactured as a separable continuous material (rollable material) and on the one hand a reduced water absorbency compared to vulkanfiberbasierten products, but on the other hand have a high tear strength and meet the test standard of DIN EN 13743 (explosive speed).

The object is achieved by providing an abrasive carrier in the form of a composite material according to claim 1 and a method for producing desselbe according to claim 11. This abrasive carrier is intended at any time by coating with abrasive (eg an abrasive grain) and applying and curing a further binder layer to be converted into an abrasive material.

Surprisingly, the inventors have found that an abrasive material made in this manner, on the one hand, does not have the disadvantages of vulcanized fiber wheels, but on the other hand is much more stable than an abrasive material obtained by directly applying an abrasive slurry to a (possibly bonded) nonwoven fabric is available. In particular, the abrasive materials that can be produced based on the abrasive backing of the present invention not only meet the necessary requirements for achieving high explosive speeds for round abrasive wheels, but are even far greater.

The cured polymer having thermosetting properties formed from the prepolymer should have a relatively high glass transition temperature Tg exceeding 80 ° C, preferably even 100 ° C. The resin solution, dispersion or suspension should be shear stable and contain about 30-65% by weight, preferably about 45-55% by weight solids; as the solvent, a water-containing solvent or water is preferable. Good film-forming properties are favorable. The resin can be selected in any desired manner, for example among the resins customary for grinding wheels; it is preferably selected from thermosetting acrylics to thermosetting resins, which may optionally be mixed with thermoplastic acrylates, and / or to phenolic resins curing resins, including in particular phenol-formaldehyde condensation resins.

The support, as mentioned, is in the form of a fiber fabric, ie it is a textile fabric in which the fibers are not interconnected by fabric bundles or meshes or the like, but is generally free or by chemical or physical processes, e.g. hereinafter subsequently interconnected - side by side and / or one above the other. Particularly preferred is a nonwoven, which may be made for example as a spunbonded, aerodynamic or hydrodynamic or carded web, or a scrim in which layers of adjacent threads are arranged at right angles or at a different angle to each other and then joined together, for example, by thermal welding. The fleece may optionally be relined or laid several times; its fibers may, but need not, be consolidated among themselves by chemical processes (in particular by the addition of a binder) or by mechanical processes, in particular needling, water-jet treatment, stretching or suturing, or by the addition of melt fibers. Also possible is a laminate of at least one nonwoven fabric and at least one scrim or a laminate of a plurality of webs or a plurality of thread layers.

The fibers of the carrier can be inorganic fibers or organic, usually synthetic fibers; in some cases it is convenient to mix them with natural fibers such as cellulose fibers. According to the invention, cellulose fibers are to be understood as fibers which have been obtained by a viscose spinning process (from the precipitation bath, for example subsequently cut). Among other things, such fibers differ from the cellulose pulp fibers used for vulcanized fibers in that they are substantially longer (usually about 20-60 mm in comparison to the about 3 mm long pulp fibers). Preferred for the present invention are, for example, polyamide (PA), polyester (PES), or glass fibers, optionally additionally in admixture with cellulose fibers. The inorganic fibers may be surface-modified, eg silanized or organically modified with alkylsilanes or the like. The natural fibers should generally be present in chemically unchanged form and in particular have no hydrate cellulose outer layer. If polyester fibers are used, the preferred material is polyethylene terephthalate (PET). Mixtures among these fibers, for example mixtures of PA and PES, PES and cellulose or PES and glass fibers, are possible. If mixtures are used, they can be evenly distributed in the fiber fabric or separated according to fiber type. An example of the latter are laminates with a first fiber layer of a first Material and a second nest of a second material. Decisive for the choice of fibers is once a good connection of the prepolymer resin or the prepolymer suspension or dispersion, and on the other hand, the thermal stability of the finished, coated with the thermoset carrier material, since the grinding produces frictional heat, depending on the application locally short-term can rise up to 800 ° C. Good results are obtained for example with a laminate of a polyester non-woven and a Glasfadengelege. The presence of the glass fibers improves the thermal stability of the composite material for later use.

In a specific embodiment, the carrier material consists of polyester fibers or of a combination of polyester and inorganic fibers, in particular glass fibers, and is coated with a thermosetting acrylate resin. This embodiment is particularly preferred because the usable for the invention acrylate resins on polyester, but also on glass surfaces, adhere well.

The support material preferably has a thickness in the range of 0.2-1.5 mm and a weight in the range of 50-800 g / m ² .

The carrier material is impregnated with the resin, e.g. soaked, or coated. When soaking, it is soaked in a relatively low viscosity resin solution. Another possibility of impregnation is the spraying of the resin solution onto the carrier material. The surfaces of the fibers are coated with the resin. For a coating, higher-viscosity formulations are generally selected, which are applied in a suitable manner to the surface of the support material and form a continuous layer there. Both variants, the wrapping of the fibers with the resin and the application of a coating on the surface of the carrier material can alternatively, if appropriate also be used cumulatively. It is advantageous to impregnate the carrier material with the resin of an aqueous dispersion / suspension, e.g. to soak, and then squeeze the excess. This can be done on a tenter or continuously on the rolling material.

In general, the resin is applied in such an amount that the prepolymer, after drying / evaporation of the solvent, depending on the carrier weight, the required material thickness and the required final weight in an amount of usually about 50-800 g / m ² draws on the carrier material.

Subsequently, the carrier material provided with the resin is dried at a temperature / a temperature profile and / or over a period of time which are below the curing temperatures and / or curing periods for the final crosslinking of the respective material. Conveniently, temperatures in the range of 80-160 ° C can be here. The drying period is usually less than an hour. Thus, the cycle time can be passed through a drying oven having a flow length of e.g. 30 m, preferably 0.5-10 min, more preferably 1 to 8 min. To obtain the smoothest possible surface and a high density, the material can then be calendered. The calendering pressure is favorably at 50-300 N / mm (line pressure), the calendering temperature is generally between ambient temperature (about 20-25 ° C) and 150 ° C.

Depending on the thickness of the support material, a sheet-like composite material having a basis weight of preferably about 100 to 1600 g / m ² and a thickness in the range of generally 0.15 to 2.5 mm, preferably about 0.2 to 1.5, is obtained mm.

Subsequently, the product may be sprinkled with abrasive particles and, after coating the particles with a layer of a top coat binder, allowed to fully cure. This cure typically takes a period of three to four days at a temperature in the range of 115-140 ° C. Sprinkling with abrasive particles may optionally be done after application of a masterbinder. This can be done either on already precut as needed in any shape shapes, for example on round discs, or the separation takes place only after final completion of the material.

It is common that the abrasive material of the composite material according to the invention is provided by the abrasive manufacturer; Of course, it is instead possible to combine both manufacturing steps in a single sequence.

The invention will be explained in more detail below with reference to several examples and a comparative example.

example 1

A web of mechanically consolidated 100% PES (eswegee nonwoven GmbH) with a basis weight of about 400-450g / m ² and 3mm thickness was on a Monforts tenter with an aqueous Phenolformaldehyddispersion (Phenodur VPR 1740 Fa. Cytec) with a solids content soaked in 50% by mass. Excess material was squeezed off; After that, the fleece had about 800g / m ² of Dispersion recorded. It was then passed at a speed of 10 sec / m over a drying section of 30 m, where it was exposed to a temperature profile of 120 ° C-180 ° C. The nonwoven thus treated had a thickness of about 1.4-1.7 mm. Subsequent calendering reduced the thickness to about 0.65-0.75 mm. The product still showed no thermosetting properties; it had a basis weight of about 800-850 g / m ² .

Example 2

Example 1 was repeated with the change that, instead of the phenol-formaldehyde dispersion, an aqueous dispersion of a formaldehyde-free Acrodur acrylate (a thermoset) from BASF was used.

Example Group 3

Example 2 was repeated with the change that instead of the formaldehyde-free Acrodur acrylate from BASF mixtures of this acrylate with (thermosetting) acrylates of different types of hardness (with glass transition temperatures between 30 ° C and 60 ° C) and a crosslinking component (a melamine or Urea resin) was repeated.

Comparative example

A vulcanized fiber material with a thickness of about 0.7 mm and a basis weight of about 800 g / m ² was treated as described in example 1. The product had a basis weight of 815 g at a thickness of only 0.66 mm.

The materials of all examples were coated in the same manner known in the art with an aqueous phenolic resole as the base binder, with abrasive grits, e.g. Corundum, sprinkled and dried. Thereafter, a capping agent composed of an aqueous phenolic resole having powdery calcium carbonate as a filler and a rheological additive (a leveling agent for reducing the surface tension) was applied over the grain for stabilization thereof. The abrasive grain coated material was dried and fully cured at 90-150 ° C, which took several days. The coating of the product had thermoset properties.

The properties of the materials according to Example 1 and Comparative Example are compared in Table I below. One recognizes an extreme Reduction of water absorption (from more than 8% to less than 1%), uniform breaking forces in the longitudinal and transverse direction and a greatly improved tear strength in both directions. The longitudinal / transverse strength ratio is over 75%, while that of a volcanic fiber plate is significantly lower. <b> Table I </ b> unit invention Comparative example thickness mm 0.7 0.66 Basis weight present g / m ² 799 815 Basis weight atro g / m ² 798 Air-conditioning after 24 hours g / m ² 802 moisture increase g / m ² 4 moisture increase % 0.5 8.1 Ratio of tensile force transverse / longitudinal factor 0.83 0.68 Breaking force along, hardened, 2h 130 ° C N / 50mm 2052 Elongation at break, hardened, 2h 130 ° C % 26.0 Tear force across, hardened, 2h 130 ° C N / 50mm 1624 Elongation at break across, hardened, 2h 130 ° C % 23.1 Ratio transverse / longitudinal factor 0.79 Tearing force along N / 50mm 32.3 12.7 Tearing force across N / 50mm 39.1 14.0 Tearing force after water storage, along N / 50mm about 45 5 Tearing force after water storage, transverse N / 50mm Approximately 49 4.5

After the maximum possible moisture absorption, the material of Example 1 was still completely flat on a flat surface, while that of the Comparative Example corrugated. This not only promises a better handling of grinding wheels made of the material according to the invention, but also gives the buyer a product whose hand signals a good function.

To measure the tearing force after water storage, the samples were each stored for a long time in water and then drained and carefully blotted off to remove water lying on the surface.

Example 4

An Example 2 based material was provided with abrasive grain as described above by first being coated with a masterbinder consisting of an aqueous phenolic resole, calcium carbonate and a rheological additive, then sprinkled with abrasive grain and dried. Thereafter, a capping agent was applied over the grain to stabilize it, which also consisted of an aqueous phenolic resole with powdered calcium carbonate as a filler and a rheological additive. The abrasive grain coated material was dried and fully cured at 90-150 ° C, which took several days. The coating of the product had thermoset properties.

The abrasive material thus obtained was subjected to an explosive speed test in accordance with DIN EN 13743 in order to determine up to which speed the material can be handled safely, without fear of collision of the disc. The explosive speed is the value in rpm at which a grinding wheel of a defined diameter is blown up by the centrifugal force. For this purpose, there are fixed, depending on the diameter of the discs norm values.

It has been found that by providing the abrasive grain-free inner composite of the present invention, a sheet of at least one layer of laid fibers coated or impregnated with a prepolymer material which exhibits thermosetting properties in the post-curing heat will provide an abrasive material can be, whose explosive speeds are far above the nominal explosive speeds, as shown in Table II below: Table II Disc diameter Practice - Speed Target explosive speed Blasting speed Example 4 mm U / min U / min U / min 115 13293 24868 26210 125 12229 22879 23112 180 8493 15888 18132

The practical speed is calculated from a rotation speed of 80 m / s. The setpoint speed contains an included safety buffer.

Finished grinding wheels based on the invention have been used for grinding narrow radii, e.g. Rain gutters in the car, welds made of iron, stainless steel and NE, used. The grinding wheels are characterized by a very high rigidity, which can be deformed for the grinding of narrow radii and does not break when resetting.

The grinding of welds (stainless steel) was compared to grinding with Vulkanfiberbasis grinding wheels according to the comparative example. The result showed advantages in terms of service life and grinding removal advantages for the present invention. Both results are based on a better grain adhesion compared to the vulcanized fiber. The grain adhesion on the material of Example 1 is in fact significantly better than that on the vulcanized fiber plate because of its less smooth and more fibrous surface and the resulting improved mechanical anchoring.

A further advantage of the composite material according to the invention was found when minor tears occurred on the grinding wheel during intensive use. While these cracks in the comparative material increased immediately, grinding wheels with the composite material according to the invention showed a significantly higher tear propagation resistance in the longitudinal and transverse directions.

An embrittlement tendency, as can be observed in Vulkanfibermaterialien due to the existing cellulose and the very short fiber lengths, is not expected for the materials of the invention.

Claims (14)

1. Elastically deformable composite material which can be further processed into sheet-like abrasive products, consisting of a sheet-like substrate made of a fibrous construction or of a laminate comprising at least one fibrous web and at least one laid scrim or a laminate comprising a plurality of fibrous webs or a plurality of laid scrims, characterized in that the substrate comprises at least one layer of laid fibers selected from inorganic fibers and organic synthetic fibers, optionally in admixture with natural fibers, and in that the substrate is coated or impregnated with a prepolymer material which acquires thermosetting properties when thermally post-cured, wherein the prepolymer material was applied onto the substrate in the form of a resin, a dispersion or a suspension and then was dried in such a way that it has not reached yet its fully cured status.
2. Elastically deformable composite material according to claim 1, characterized in that the substrate exclusively comprises laid fibers.
3. Elastically deformable composite material according to any of the preceding claims, characterized in that the fibers have the shape of a single-layer or multi-layer fibrous web, or of a single-layer or multi-layer laid scrim, or of a combination of at least one fibrous web and one laid scrim.
4. Elastically deformable composite material according to any of the preceding claims, characterized in that the material of which the fibers are made is selected from polyesters, polyamides, glass fibers which can be surface-modified, mixtures comprising a plurality of these fibrous materials or mixtures comprising one or a plurality of these fibrous materials and cellulose.
5. Elastically deformable composite material according to claim 3 or 4, characterized in that the substrate is a laminate of at least two identical or different layers.
6. Elastically deformable composite material according to claim 5, characterized in that one of the layers is a fibrous web and a second layer is a laid scrim.
7. Elastically deformable composite material according to any of claims 5 and 6, characterized in that one of the layers comprises polyester fibers and a second of the layers comprises glass fibers.
8. Elastically deformable composite material according to claim 1, characterized in that the prepolymer material was applied from the aqueous phase.
9. Elastically deformable composite material according to claim 1 or 8, characterized in that the prepolymer material is an acrylate material which upon curing becomes a thermosetting polymer, said acrylic material optionally being mixed with a thermoplastic acrylate material, and/or that the prepolymer material is a resin which upon curing becomes a phenolic polymer, in particular a phenol formaldehyde resin produced by condensation.
10. Elastically deformable composite material according to claim 1, having a thickness of 0.15 - 2.5 mm, preferably of 0.20 - 1.5 mm, and/or a grammage of 100 to 1600 g/qm.
11. Method for the manufacture of an elastically deformable composite material according to any of the preceding claims, characterized by the following steps:

    (i) Providing a substrate as defined in any of claims 1 to 7,

    (ii) Impregnating the substrate in a solution, suspension or dispersion which contains the mentioned prepolymer material,

    (iii) Optionally stripping off excess amounts of solution, suspension or dispersion,

    (iv) Drying the soaked substrate,

    (v) Optionally calendering the dried substrate.
12. Method according to claim 11, characterized in that the solution, suspension or dispersion of the prepolymer material comprises a solids content of 25-65 % by mass, preferably of 35-50 % by mass.
13. Method according to claim 11 or 12, characterized in that drying of the soaked substrate is performed within up to 4 hours at 80-160° C such that the prepolymer material does not acquire any thermosetting properties yet.
14. Method according to any of claims 11 to 13, characterized in that the calendering is performed at a pressure of 50-300 N/mm at 25-150° C.