WO2005063445A1

WO2005063445A1 - Method and plant for manufacturing flexible abrasives, as well as flexible abrasive manufactured with said method

Info

Publication number: WO2005063445A1
Application number: PCT/IT2003/000858
Authority: WO
Inventors: Claudio Lesizza
Original assignee: Impianti Macchine & Tecnologie S.R.L.
Priority date: 2003-12-29
Filing date: 2003-12-29
Publication date: 2005-07-14
Also published as: AU2003300748A1; EP1699597A1

Abstract

Plant and method for manufacturing flexible abrasives, which carry out or comprise the following operative steps: applying a first adhesive layer (5) onto a flexible support (2); applying an abrasive material (6) onto the first adhesive layer (5); reticulating the first adhesive layer (5) in a furnace (9); applying onto the abrasive material (6) two or more overlapping adhesive layers (11), each of which is reticulated in a furnace (14) before the application of the subsequent adhesive layer (11).

Description

"METHOD AND PLANT FOR MANUFACTURING FLEXIBLE ABRASIVES. AS WELL AS FLEXIBLE ABRASIVE MANUFACTURED WITH SAID METHOD" The present invention relates to a method for manufacturing flexible abrasives and in particular abrasive tapes, as well as a manufacturing plant which carries out said method and a flexible abrasive manufactured with said method. The known methods for manufacturing abrasive tapes on supports of paper, cloth, fibre or combinations thereof, or on synthetic supports, consist of applying a first adhesive layer, generally phenolic, on the flexible support, whereon the abrasive material in a granular form is then applied. At this point the flexible support is subjected to a first thermal treatment in a hot air-circulating furnace. The flexible support, hanging in festoons, is passed through said furnace, so as to be heated from the room temperature to a temperature of about 130°C through fixed temperature increments. At the end of the thermal treatment, that can last from 30 minutes to 3 hours, the first layer of adhesive is hardened. To ensure the fixing of the abrasive material, a second adhesive layer, called covering adhesive, is applied onto the flexible support. Afterwards, the flexible support is subjected to a second thermal treatment in conditions analogous to the first, but for a period of time from three to six hours. Finally the product is rolled up in bobbins and subjected to a continuous reticulation that lasts several hours. In order to obtain a sufficient productive capacity, said known methods require furnaces of big size, especially if phenolic adhesives are used. As a matter of fact, these last, being particularly sensitive to thermal gradients, require drying rooms which are often longer than 200 meters and, therefore, high installation and production costs. As a matter of fact, if the furnaces are shorter, and thus the variations in temperature faster and the thermal gradients of greater amount, steam bubbles may be formed, due to a too quick evaporation of the solvent, which make the surface of the adhesive layers craped and damage the compactness thereof. Since the product in drying rooms is hanged in vertical position, quick increments of temperature may also cause the reduction of viscosity of the adhesive and thus the sliding thereof along the surface of the support, thus compromising the homogeneity of the product and the functionality thereof. Another disadvantage of the above described known methods lies in that it is necessary to use sophisticated and expensive ventilation systems to obtain an homogeneous temperature distribution over the whole product hanged in festoons. In order to solve these problems, some flexible abrasives manufacturers thought to use a layer of non phenolic adhesive. In this way it is possible to reduce the size of the festoons furnaces or even to replace them with linear furnaces with a much smaller size. However, the non-phenolic adhesives have worse mechanical properties in terms of tenacity, hardness, resilience, thermal stability and water resistance. In some cases, as for example in the manufacture of impermeable fabrics for wet- workings, the use of phenolic adhesives is unavoidable. Furthermore, the phenolic adhesives are the cheapest ones among those suitable for manufacturing flexible adhesives. - Thus, some manufacturers of abrasives thought to use phenolic adhesives with additives, such as polyvinyl alcohol in an aqueous solution, cellulose derivates, starch or starch derivates, suitable for reducing the times of the drying process of the phenolic resin. In this way the drying time of the adhesive is partially reduced, but the process is still long because of the last step of reticulation to which the product has, anyway, to be subjected. In order to reduce the duration of said reticulation step, the technique of acidizing the phenolic resin with p-toluensulfonic acid is largely widespreadly, which, on the contrary, causes an impoverishment of the mechanical properties. EP 591902 describes the use of a phenolic adhesive of high molecular weight (1400-3500) diluted with a higher boiling organic solvent, as for example cyclohexanone or ethoxyethanol, for manufacturing abrasives by means of linear furnaces and hence with quicker drying processes. Even this method, however, does not solve the problem concerning the long duration of the reticulation step. Other solutions have been proposed during years, among which the use of microwave or ultraviolet. However, they need complicated installations and obtain products with mediocre mechanical characteristics. A further disadvantage of all the known methods for manufacturing flexible abrasives and of the relevant manufacturing plants lies in that they adapt with difficulty to the numerous variations of the production due to the numerous types of abrasives required by the market. The object of the present invention is therefore to provide a method and a plant for manufacturing flexible abrasives, which are free from the above mentioned drawbacks. This object is achieved with a plant, a method and a flexible abrasive, the main features of which are specified in claims 1, 8 and 13, respectively, while other features are specified in the remaining claims. The method for manufacturing abrasives according to the present invention comprises the application of several thin layers of covering adhesives, which therefore reticulates in a short time and in small furnaces without requiring sophisticated ventilation systems, with consequent remarkable economic advantages. The flexible abrasive obtained with the method according to the present invention, being provided with several adhesive layers, has excellent mechanical characteristics. Another advantage of the method according to the present invention is the possibility to use traditional phenolic adhesives, with consequent advantages from the economic point of view as well as from the point of view of the properties of the product obtained therefrom. Further advantages and features of the method for manufacturing flexible abrasives and of the relevant manufacturing plant according to the present invention will be clear to those skilled in the art from the following detailed and non-limiting description of one embodiment thereof with reference to the attached drawings wherein:

- figure 1 shows a schematic side view of a plant for manufacturing flexible abrasives according to the present invention; and

- figure 2 shows a schematic sectional view of a flexible abrasive manufactured with the method according to the present invention. With reference to these figures, there is shown that the plant for manufacturing flexible abrasives according to the present invention comprises in a known way an unwinding machine 1 suitable for unwinding a flexible support 2 winded in a bobbin. After passing through a printer 3 which prints the trade mark or other signs onto the back of the flexible support 2, the latter passes through a first gluing machine 4 suitable for depositing a first layer 5 of adhesive. Said gluing machine 4 may be of any known type, for example with cylinders, with a wiping blade, a spray type, a film type, ecc, while the adhesive may be a animal or vegetal gelatin, a urea-formol resin, a melaminic, acrylic, alkilyc, epoxidic, urethanic, phenol-formaldehyde resin, or any other substance of a known type. An abrasive material 6 in a granular form is applied on the adhesive layer 5, still in a liquid state. Said abrasive material 6 may be a natural product as garnet or naxos or a synthetic product as aluminum oxide or silicon carbide in several forms (alumina zirconium, CBN diamond, ecc). It may be applied by means of gravity on the adhesive layer 5 or by using electrostatic force or any other known method. In the embodiment shown in figure 1, the plant is provided with two different systems for applying the abrasive: a sprinkler 7 which exploits the gravity force and an electrostatic device 8. It allows to use abrasives with different characteristics by selecting the more suitable application system or to use simultaneously the two systems, if necessary. Once the abrasive material 6 has been applied, the flexible support 2 is subjected to a first thermal treatment which may be carried out through convection, conduction, irradiation or combinations thereof. According to the preferred embodiment of the present invention, this thermal treatment takes places in a furnace 9 with an infrared radiating surface, in particular gas-powered panels emitting infrared rays. Said thermal treatment in furnace 9 allows to quickly obtain the temperature required for the complete reticulation of the adhesive layer 5 without damaging it. The so obtained abrasive tape 10 is suitably subjected to at least two further treatments of applying and drying adhesive layers 11. These treatments take place in two or more modular apparatuses 12 arranged in series downstream furnace 9. In the present embodiment, the modular apparatuses 12 are three. Each modular apparatus 12 has a gluing machine 13 and a furnace 14, preferably of the type with an infrared radiating surface. The gluing machine 13 comprises two cylinders, at least one of which coated with rubber, and a wiping blade fitted for making the applied adhesive layer homogeneous. The gluing machine 13 can be adjusted so as to apply thin adhesive layers 11, in particular having a thickness lower than 100 micron. In fact, the adhesive layers 11 must have such thicknesses that the adhesives coming out from the furnaces 14 are completely reticulated, so as to avoid to subject the finished products to a subsequent step of discontinuous reticulation. The finished tape 10 coming out from the last modular apparatus 12 is wound again in a bobbin through a winding machine 15. The modular apparatuses 12 according to the present embodiment of the invention comprise preferably ventilation means 16, arranged upstream furnaces 14, fitted for uniformly distributing the adhesive layer 11 applied by the gluing machines 13. In particular said ventilation means 16 comprise a blowing machine which emits an air jet on the surface of the adhesive layer 11. The method for producing flexible abrasives according to the present invention comprises substantially the following operative steps:

- applying a first adhesive layer 5 on a flexible support 2;

- applying an abrasive granular material 6 on the first adhesive layer 5;

- drying the first adhesive layer 5 in a first furnace 9;

- applying onto the abrasive material 6 at least two overlapping adhesive layers 11, each of which is reticulated in a furnace 14 before the application of the subsequent adhesive layer 11. The flexible support 2 may be made of any known suitable material. The most used materials for carrying out the flexible support 2 are paper, fibre, cotton fabric, synthetic fibre fabric, other synthetic means or a combination thereof. The adhesive layers 11 may be of a different type so as to obtain combinations which confer to the obtained products particular mechanical characteristics as the resilience or the molecular rigidity as well as an high abrasion index. The following example, provided for explanation and not for limitation purposes, will allow to better understand the invention. EXAMPLE 1 Two samples A, B of flexible abrasives, generally used to carry out abrasive disks for the industries working in the fields of coachwork, metallic carpentry, marble processing and wood processing, were manufactured. A phenolic resin in an aqueous solution, corresponding to the commercial product 9190 produced by the firm "Bakelite", was used as adhesive. Aluminum oxide of the type BFRPL-CC with a 24P grain, produced by the firm

"Treibacker", was used as abrasive. An adhesive layer 5 of 280 g/m² and then 1300 g/m² of abrasive material 6 were wet-applied onto the paper support 2. The sample A was dried in a traditional furnace with an increasing temperature from 80°C to 100°C for a period of 60 minutes. When the resin became hard, a covering adhesive layer was applied and the product was subjected to a thermal treatment analogous to the first one with temperatures from 80°C to

130°C for 180 minutes. The sample B, instead, was subjected to a drying treatment in an infrared furnace 9 for 60 seconds. At tins point the adhesive was aheady hardened and thus three covering adhesive layers 11 were applied, having a thickness of about 100 micron, in three subsequent steps of 60 seconds each, each followed by a drying step in an infrared furnace 14. Said furnace 14 comprised a porous means in sintered metallic fibres; the radiating surface was at the temperature of 800°C; the wavelength of the emitted rays was comprised between 2,5 and 3 micron. At the end of each thermal treatment, the applied adhesive layer 11 was compact and free from craters or bubbles caused by the rapid evaporation of the solvent. The two samples A and B were kept for 24 hours in the same room and then subjected to efficiency tests. For this purpose a steel plate Cr-Ni-18\8 with a thickness of 3 mm as material to be abraded and a disk polisher with a peripheric velocity of 60 m/s, a pressure of 80 N and an angle of incidence on the edge of the plate of 25 °C, were used. Both the samples A, B were subjected to tests of the duration of 8 minutes. These tests showed that the abrasion index of the sample B, expressed as amount of abraded material per unity of weight lost by the disk, was notably higher than the abrasion index of sample A. As a matter of fact, for the sample B, manufactured with the method according to the present invention, said index was equal to 24,2 while the abrasion index for the sample A manufactured with the traditional method was 10,8. Possible changes and/or additions may be made by those skilled in the art to the embodiment of the invention hereinabove described and illustrated without departing from the scope of the same invention.

Claims

CLAΓMS

1. A plant for manufacturing flexible abrasives on supports comprising a gluing machine (4) suitable for applying onto a flexible support (2) a first adhesive layer (5) which is reticulated in a first furnace (9) after the application of an abrasive material (6) on the surface thereof by means of at least one applying device (7, 8), characterized in that it comprises at least two modular apparatuses (12) arranged in series downstream the first furnace (9), each of which is provided with a gluing machine (13) which is suitable for applying an adhesive layer (11) onto the abrasive material (6) and is arranged upstream a further furnace (14) suitable for reticulating said adhesive layer (11).

2. A plant according to claim 1, characterized in that the modular apparatuses (12) comprise ventilation means (16), arranged upstream the furnace (14), suitable for uniformly distributing the adhesive layer (11) applied by the gluing machine (13).

3. A plant according to claim 1 or 2, characterized in that the gluing machine (13) of a modular apparatus (12) comprises two cylinders suitable for applying an adhesive layer (11) and is provided with a wiping blade suitable for making this adhesive layer (11) homogeneous.

4. A plant according to one of the previous claims, characterized in that said applying device (7, 8) for the abrasive material (6) is based on the use of the gravity or electrostatic force.

5. A plant according to one of the previous claims, characterized in that the applying devices (7, 8) for the abrasive material (6) are two and may be actived alternatively or simultaneously.

6. A plant according to one of the previous claims, characterized in that the furnaces (14) of the modular apparatuses (12) are infrared furnaces.

7. A plant according to one of the previous claims, characterized in that the modular apparatuses (12) are three.

8. A method for manufacturing flexible abrasives, characterized in that it comprises the following operative steps: - applying a first adhesive layer (5) onto a flexible support (2);

- applying an abrasive material (6) onto the first adhesive layer (5);

- reticulating the first adhesive layer (5) in a furnace (9);

- applying onto the abrasive material (6) two or more overlapping adhesive layers (11), each of which is reticulated in a furnace (14) before the application of the subsequent adhesive layer (11).

9. A method for manufacturing flexible abrasives according to claim 8, characterized in that the thickness of the further adhesive layers (11) is lower than 100 micron.

10. A method for manufacturing flexible abrasives according to claim 8 or

9, characterized in that the furnaces (14) for reticulating the further adhesive layers (11) are infrared furnaces.

11. A method for manufacturing flexible abrasives according to claim 10^', characterized in that the temperature of the radiating surface of the furnaces (14) is comprised between 700°C and 900°C 12. A method for manufacturing flexible abrasives according to one of claims 8 to 11, characterized in that one or more further adhesive layers (11) comprise a phenolic adhesive. 13. A flexible abrasive comprising a flexible support (2) provided with at least an adhesive layer (5) whereon an abrasive material (6) is placed, characterized in that at least two overlapping adhesive layers (11), which are singularly reticulated, are applied onto the abrasive material.