SE521880C2 - Method of making a film material and abrasive material made according to the method - Google Patents

Abstract

The present invention concerns a method of producing a film material comprising the steps of creating at least a first, a second and a third mixture, leading each one of the mixtures to a co-extrusion die (1,10) and co-extruding the mixtures through the die (1,10) in order to produce a co-extruded film containing at least a first (5), a second (6) and a third (7) layer respectively. At least the mentioned second mixture comprises a blowing agent at the same time as the mentioned second mixture forms the mentioned second (6) layer in the co-extruded film. The mentioned first mixture comprises particles (8) each one of which being, in each direction, of a thickness which is larger than the thickness of the mentioned first (5) layer without the particles (8) meaning that the particles (8), through the expansion of the blowing agent in the mentioned second (6) layer, being pressed out upon the surface of the mentioned first (5) layer and creating unevennesses in the surface layer there. The present invention also concerns an abrasive material produced in accordance with the method.

Description

at least said second mixture comprises a blowing agent while said second mixture forms said second layer in the coextruded film and said second layer is surrounded by at least said first layer on one side and at least said third layer on the second side. Said first mixture comprises particles each in each direction having a thickness exceeding the thickness of said first layer without the particles meaning that the particles, by expansion of the blowing agent in said second layer, are pressed out on the surface of said first layer and there forms irregularities in the surface layer.

Said blowing agent may expand as it leaves said nozzle.

Said blowing agent may consist of a chemical blowing agent of endo- or exothermic type.

Said particles can have a size of 5-500 hours. Said particles may consist of alumina, silicon carbide, zirconium alumina, broken glass, sapphire, garnet and / or diamond.

Said third layer may be stiffer than said first layer. Said third layer may be thicker than said first layer. Said third polymer may have a viscosity which is higher than the viscosity of said first polymer.

Said co-extrusion nozzle may consist of a nozzle ring included in an equipment for blowing film. Said co-extrusion die may be a flat die forming part of a film casting equipment.

The invention thus also comprises an abrasive material for finishing processing and which is manufactured in accordance with the method as above, wherein the abrasive material has at least one surface layer which has irregularities which consist of particles in a first layer in a coextruded film comprising at least three layers. Said first layer with particles when using the abrasive material springs slightly against a second porous layer containing blowing agent and located between said first layer and a third layer in said coextruded film.

List of figures Figure 1 shows, in cross section, a co-extrusion nozzle during plane extrusion according to the prior art.

Figure 2 shows, in cross section, the co-extrusion nozzle according to Figure 1 during plane extrusion according to the invention. - ~. . i. »521 880 3 Figure 3 shows, partly in cross-section, equipment for blowing fi ch according to the state of the art.

Figure 4 shows, in cross section, a part of the equipment for blowing mlm according to figur 3 during blowing according to the invention.

Description of embodiments Figure 1 shows a previously known co-extrusion nozzle 1 during plane extrusion according to the prior art of fi ch. In three channels 2, 3 and 4, three more or less different but known compounded materials, each comprising a polymer, flow and are co-extruded through the flat die into a laminate comprising three layers 5, 6 and 7. Co-extrusion nozzles exist for this purpose. - well more and fewer layers. The layers according to the figure all have the same thickness, but this can also vary. The vidare figure further shows that each of the layers is of substantially the same thickness near the nozzle as a piece from the same, which characterizes plane extrusion according to the prior art.

Figure 2 shows the known co-extrusion nozzle 1 during plane extrusion according to the invention. During extrusion, an abrasive material is produced. In the channel 2 flows a compounded material based on a thermoplastic polymer containing 1-80% abrasive in the form of particles 8 of some alloy or some mineral.

Suitable thermoplastic polymers are polyolines, polyester, polystyrene, polycarbonate, polyamide, polyurethane, EVA, EMA, EBA, thermoplastic elastomers such as SBS and EPDM and the like. Suitable materials for the particles 8 are alumina, silicon carbide, zirconia, broken glass, sapphire, garnet, diamond and other hard materials according to the Mohr scale. The particle size can be 5-500 μm.

In order for the particles to be chemically coupled to one or more of their thermoplastic polymers, the particles are first surface-treated with silanes, titanates or peroxides in a high-speed mixer of, for example, one of the Henchel or PMI brands. After mixing particles and polymer, the material is compounded in a single or double screw extruder of, for example, one of the brands Berstorff or Leistritz together with different types of additives and process aids. Polymer type, additives and process aids vary and are combined from case to case. The compounding means that the particles are dispersed into primary particles and distributed in the polymeric material comprising said additives and process aids and that the mixture is extruded, cooled and cut to normal granulate size, a form which is then easy to use in the final production of the abrasive material. Suitable additives are pigments, reinforcement, UV stabilizers, antioxidants, compression modulators, antifoulants, plasticizers, antistatic agents and the like. Suitable process aids are lubricants, surfactants, fluoroelastomers and the like. In the channel 3, a mixture based on a thermoplastic polymer flows with a balanced melt viscosity, in view of the polymer types in the channels 2 and 4. The thermoplastic polymer contains a balanced amount of endo- or exothermic type chemical blowing agent. The blowing agent as well as additives and process aids are added to the polymer material in the form of concentrate, so-called masterbatch.

In the channel 4 flows a mixture based on a thermoplastic polymer which may be mixed with filling material in the form of dolomite, calcium carbonate and / or talc. The mixture also contains additives and process aids. All or parts of the filling material can, if desired, be replaced with iron powder which has been magnetized to give the end product the advantage of being easily mounted on grinding tools adapted for such magnetic mounting.

When the mixtures flowing in the channels 2, 3 and 4 leave the extrusion die 1, they form a laminate film where the layer 5 with the particles 8 eventually forms the actual grinding layer in the desired grinding material. In order for the particles 8 to really give an abrasive effect in the layer 5 in the finished abrasive product, it is required that the particles 8 are superimposed on the surface of the layer 5 and form unevenness in the surface layer. This movement is effected by the blowing agent in the layer 6, as soon as it leaves the extrusion nozzle 1, expands and thereby pushes the particles 8, which from the beginning near the nozzle 1 partially extend into the intermediate layer 6, completely out of the intermediate layer 6. Each of the abrasive particles 8 is large enough to extend from the bottom level of the layer 5 to and past the top level of the layer 5 regardless of how the particles are turned and twisted. The particles will thus form the desired irregularities in the surface layer and these irregularities are only covered by an extremely thin layer of polymer which mainly follows the shape of the irregularities and which is attributable to the above-mentioned chemical coupling between particles and polymer. The expansion of the blowing agent in the layer 6 can be directed mainly towards the layer 5 by making the second outer layer 7 stiffer and / or thicker than the layer 5 or by controlling the viscosity of the materials in the melt. The blowing agent expands more or less continuously up to the point where the material has solidified / crystallized, the so-called frost line 9. It is important that the abrasive particles 8 are allowed to move freely to and through the top level of the layer 5 without any cooling roller preventing the process. .

Figure 3 shows equipment for blowing ch according to the state of the art. An annular coextrusion die 10 is here directed upwards. The nozzle blows a balloon-like body 11 whose wall consists of all the layers included in the laminate. The laminate is collected between nip rollers 12, corona-treated at 13 - ie treated with strong UV light to break down the surface - and collected on pick-up rollers. The film can also be antistatically treated and / or printed (with color or the like) before rewinding. Figure 4 shows the known equipment for blowing film during the production of an abrasive material according to the invention. Three layers are used in the laminate as previously described in connection with plane extrusion. Consequently, three extruders (not shown) feed via three channels (not shown) the coextrusion nozzle 10 and what has been stated above regarding materials and procedures in connection with plane extrusion may also apply to the case of blowing film. It should be noted that the layer 5, comprising particles and constituting the abrasive layer in the finished product, can constitute the outside of the balloon-like body 11, as in Figure 4, or its inside. If the layer 5 constitutes the inside of the balloon-like body 11, the wear on the nip rollers 12, which are usually made of a rubber material, is less worn. It may also be possible to corona-treat the back of the laminate to facilitate subsequent color printing and / or gluing of the laminate and even in that case it is an advantage if the layer 5 with the abrasive particles 8 is laid as an inner layer during blowing.

The choice, whether the layer 5 with the abrasive particles 8 is to lie in the outer or inner layer, is often practically governed by what machine equipment is available. If one chooses to lay the layer 5 with the abrasive particles on the inside during the blowing, this is most easily achieved by passing the material which gives the layer 5 to the extruder which gives the inner layer according to Figure 4 while leading the material giving the layer 7 to the extruder which gives the outer layer in the same figure, ie layers 5 and 7 change place in relation to what appears from figure 4. In the following an embodiment is given with regard to the production of blown fi lm. To the extruder for layer 5 was added a compounded composition containing:% Alumina (particle size 150 μm) 1% coupling agent (silane) 521 880 6 1% process aid (eg metal stearates) 78% polymers with low viscosity melt (soft) o To extruder for layer 6 was added a composition containing:% Blowing agent concentrate in masterbatch form (modified azodicarbonamide) 95% polymers with high viscosity melt (hard) o To extruder for layer 7 was added a compounded composition containing: 50% Ta | k and dolomite 50% polymer with high viscosity melt (hard) After the annular co-extrusion die 10 and the other process steps described in connection with Figure 3, a blown film with a thickness of 250 μm was obtained of which the layer 5 (the grinding layer in the finished product) showed a thickness about 70 pm, the intermediate layer 6 110 pm and the layer 7 finally 70 pm.

The number of layers in the laminate can be varied within fairly wide limits as long as the abrasive layer is at the extreme on some side and at least one layer containing blowing agent forms some of the intermediate layers. However, the number of layers recommended is 3-7, whereby a blown film for the described purpose may have a total thickness of 60-500 μm.

Because the use of described blowing agents is relatively simple, the production of raw material / abrasive material becomes rational and very economical in the manner described. Regardless of whether the abrasive material is produced by plane extrusion or by blowing, the particles in the abrasive layer 5 and the entire abrasive layer 5 become slightly resilient when the abrasive material is used, depending on the action of the blowing agent. This increases the efficiency in use of the abrasive abrasive material compared to a material with a dull base for the abrasive layer.

The invention is not limited to the embodiments shown here but can be varied within the scope of the appended claims.

Claims (11)

20 25 30 521 880 PATENT REQUIREMENTS A method of making a film material comprising the steps of forming at least a first, a second and a third mixture comprising at least a first, a second and a third polymer, respectively, leading each of the mixtures to a co-extrusion die (1, 10) and co-extruding the mixtures through the die (1, 10) to produce a co-extruded film consisting of at least a first (5), a second (6) and a third (7) layer, at least said second mixture comprising a blowing agent while said second mixture forming said second (6) layer in the coextruded film and said second (6) layer being surrounded by at least said first (5) layer on one side and at least said third (7) layer on the other side, characterized in that said first mixture comprises particles (8) each in each direction having a thickness exceeding the thickness of said first (5) layer without the particles (8) implying that the particles (8) , by the expansion of the blowing agent in said second (6) layer, is pressed out on the surface of said first (5) layer and there forms irregularities in the surface layer. Method according to claim 1, characterized in that said blowing agent expands as it leaves said nozzle (1, 10). Method according to any one of the preceding claims, characterized in that said blowing agent consists of a chemical blowing agent of endo- or exothermic type. Method according to any one of the preceding claims, characterized in that said particles (8) have a size of 5-500 μm. Method according to any one of the preceding claims, characterized in that said particles (8) consist of alumina, silicon carbide, zirconia, broken glass, sapphire, garnet and / or diamond. Method according to any one of the preceding claims, characterized in that said third (7) layer is stiffer than said first (5) layer. 10 15 20 521 880 sE 0101339-0 3 Method according to any one of the preceding claims, characterized in that said third (7) layer is thicker than said first (5) layer. Method according to any one of the preceding claims, characterized in that said third polymer has a viscosity which is higher than the viscosity of said first polymer. Method according to any one of the preceding claims, characterized in that said co-extrusion die (10) is constituted by a die ring (10) included in a film blowing equipment. Method according to any one of claims 1-8, characterized in that said co-extrusion die (1) consists of a flat die (1) included in a film casting equipment. Abrasive material for finishing processing and manufactured according to the method according to any one of the preceding claims, wherein the abrasive material has at least one surface layer which has irregularities which consist of particles (8) in a first (5) layer in a co-extruded film comprising at least three layers , characterized in that said first (5) layer with particles (8) when using the abrasive material springs slightly against a second (6) porous layer containing blowing agent and located between said first (5) layer and a third (7) layer in said coextruded Film.