DK173918B1 - Method and apparatus for making composite sheets - Google Patents

Description

DK 173918 B1

The present invention relates to a process for making composite sheets as described in the preamble of claim t. The invention also relates to an apparatus for making composite sheets.

5 It is known technology to make composite sheets from matrices made of threads of various materials. A widely used method is to make these sheets in molds by heat and pressure of the die with or without an adhesive component. In cases where a glue component is not used, the yarns consist of a polymer which is melted under heat, after which the finished plate appears after cooling and curing. In order to reinforce the material, it is known to mix polymer wires and glass fibers where the polymer wires are melted during the composite molding, whereby the polymer encloses the non-melted glass fibers which subsequently act as reinforcing material.

In order for composite sheets to be made with a smooth and flat surface and an approximately homogeneous thickness, it is necessary to use fibers that are long and arranged well, that is, the wires have certain preferred directions, for example at certain angles relative to the web direction. Such matrices are called tissues. This term covers not only matrices that are woven, but also matrices in which long, orderly threads are joined by sewing. The term fabric is used for long-fiber composites as opposed to "non-woven" materials, which are blends of short fibers used, for example, for insulation mats.

To produce composite sheets in long webs, a so-called tape press can be used, as is known, for example, from international patent application WO97 / 26397. A matrix 25 of threads is passed through a heating process and a pressing process in which the pressing process takes place between pressure rollers, about which strips run, so that the composite sheet in web form is formed between strips on each side of the plate. However, tape presses are very expensive devices, which is why other devices have been developed to make composite sheet sheets without the use of the bands around the rollers.

30 These devices cost only a small fraction of the equivalent tape presses.

DK 173918 B1 2

Such an apparatus is described in Norwegian patent application NO 984275 with original international patent application W098 / 31857. In this apparatus, composite sheets are formed in web form from a web of polymer threads and reinforcing threads, preferably glass fibers. The tissue is passed through a first heating zone where the tissue is heated by heat radiation to a first temperature. Then, the web is passed over a number of hot rods which heat the web to above the melting temperature. After this heating step, the tissue is cooled and subjected to pressure to form the composite plates themselves. During pressing, the molten polymer settles around the glass wires, forming the composite with a more or less smooth surface.

10

This method has some disadvantages. In order to effect a complete melting of the tissue, the tissue is subjected to a strong heat radiation in a preheating step. This preheating step has the disadvantage of obtaining a temperature on the outside of the tissue which is around the degradation temperature of the polymer, e.g. 230 ° C for polypropylene, shortened PP while the temperature in the middle of the tissue is much lower, e.g. 140 ° C, and often below the melting temperature, which for PP is 165 ° C. Thus, the tissue undergoes degradation of the outer polymer fibers, which is highly undesirable, but which is accepted to obtain the necessary heating to the final temperature at which the polymer is fused to composite.

20

A further disadvantage when the tissue is heated to melt temperature first and then pressed at a lower temperature is the lack of homogenization in the material. Homogenization is the function where the polymer completely melts and then encloses the reinforcing material. Prior art systems need to run at a high speed 25 to minimize the time between heating and subsequent pressing with the cold rollers. However, at high speed, the tissue cannot be heated to the correct working temperature, which is well above the melting temperature and preferably close to the decomposition temperature. This is one of the reasons why preheating steps with heat radiation are used in known systems. However, this problem has not yet been completely resolved, as a rapid process speed results in poor heating and unsatisfactory homogenization of the material, while a slow process speed results in better heating, but in time, until 3 knows when the pressing rollers are long, whereby the pressing takes place at too low a temperature, which also results in unsatisfactory homogenisation.

SUMMARY OF THE INVENTION It is an object of the invention to provide a method and apparatus for producing composite sheets of a tissue where the above-mentioned disadvantages are avoided and where the heating of the tissue is preferably carried out without heating with heat radiation.

This object is achieved by a method of the type mentioned in the introduction, which is distinctive as described in the characterizing part of claim 1.

10

By incorporating one or more hot rollers heated to the hot rolling temperature, the pressing process ensures that the pressing takes place while the polymer is melted. This is an important aspect as it minimizes the void volume of the final composite plate. The void volume is the volume of air in the compost. The larger this 15 cavity volume, the less strength the composite plate has.

Furthermore, it is ensured that the individual reinforcing wires in the composite plate are enclosed as far as possible and preferably completely by the first molten and subsequently solidified polymer.

By optimum wrapping of the reinforcing material, the highest strength of the material is obtained.

In another embodiment, the invention is characterized in that the fabric comprises yarns of polymer, preferably PP, PET or PTFE, as well as yarns of a reinforcing material, preferably glass fibers, but carbon fibers or fibers of other material could also be used.

In a further embodiment, the invention is characterized in that the proportion of glass filaments in the tissue is between 55% and 75%, preferably between 60% and 70%, and most preferably 60%.

By using a tissue where the proportion of the reinforcing material, such as glass, is high, a very high strength is obtained in the material. On the other hand, it is difficult to obtain a smooth surface of the material at a high proportion of the reinforcing material. Thus, the choice of the proportion of the reinforcing material is a compromise between these two considerations. It has been found surprisingly that if the proportion of glass fibers in a tissue also consisting of polymer fibers is close to 60%, then the strength of the tissue is very high, while it is still possible to make the composite plates with a very smooth surface.

In a further embodiment, the invention is characterized in that the hot rolling temperature is between 0 ° - 20 ° below the decomposition temperature of the material having the lowest decomposition temperature, preferably between 0 ° and 10 ° below the decomposition temperature and most preferably between 0 ° and 6 ° below the decomposition temperature. . The decomposition temperature of PP is 220 ° C. Heating above this temperature promotes a degradation process of the fibers. Therefore, it is important that the polymer is not heated higher than the decomposition temperature. On the other hand, it is important for the polymer to be as viscous as possible so that the polymer finally encloses the reinforcing fibers sufficiently.

In a further embodiment, the invention is characterized in that the hot-rolling set pressure is between 20 N / mm and 50 N / mm, preferably between 20 N / mm and 40 N / mm, and most preferably 30 N / mm. The pressure is given in units of force per mm of roll length. The pressure in the pressing process must be carefully adjusted to the production speed and temperature of the composite material. At low temperature, the polymer is viscous and more pressure is required to disperse the liquid polymer, while the high temperature composite must not be subjected to high pressure as it will destroy the structure of the smooth composite web. It has been found that the pressure in a method according to the invention is very convenient 30 N / mm.

In a further embodiment, the invention is characterized in that the process speed is between 0.5 m / min and 2 m / min, preferably between 1.4 and 1.6 m / min. It is desirable to have a high production rate, as the product can thereby be manufactured in the shortest possible time. In particular, in a pressing process comprising both hot rolls and cold rolls, it is important that the composite sheet is transported from the hot process to the cold pressing process before the material has cooled so much that sufficient homogenization and molding can no longer occur. the material of the last pressing process with cold rollers. However, the production must not be so rapid that there is no satisfactory homogenization, that is, the flow of the polymer and the enclosure of the glass fibers. In this context, by cold is meant a temperature significantly below the melting temperature of the polymer. By heating the fabric with rollers and maintaining this temperature during pressing with the hot rollers, it is possible to run at a sufficiently low speed to ensure a satisfactory homogenization of the molten material. By using a pressing process where the pressure roller has the hot rolling temperature, the composite plate still has a temperature at which the polymeric material is melted as it leaves the part of the pressing process comprising the hot roller, which has been found to be a great advantage.

In a further embodiment, the invention is characterized in that the heat transfer to the tissue by heat transfer from at least one hot roll to the tissue upon contact of the tissue with the hot roll constitutes between 80% and 100%, preferably 100%, of the total heat supply. during the heating process.

15

By using the method according to the invention in which the fabric is heated by heat from rollers with hot roll temperature and where the fabric is pressed by a roll with hot roll temperature, it has surprisingly been found that the composite made according to the invention has a much higher stiffness than corresponding previously made composite sheets, which is a sign of good casting. A high stiffness of the material is advantageous when composite panels are included as components of larger complex structures where the composite panel is desired to contribute to the structural stability.

The stiffness is expressed by the so-called E-module, which is the ratio of a pressure or tensile effect on the material in the longitudinal direction of the composite plate and the corresponding relative length extension. With a certain tensile effect of the composite plate, the E-module is larger, the smaller this plate is extended as a result of the draft.

Measurements have been made of the composite sheet E module, which has been removed by a method according to the invention and with an orthotropic fiber backing material for the reinforcing material, wherein the fiber distribution in the web was 50% longitudinally and 50% transverse. . The value of the E-module has been measured at 14 GPa.

DK 173918 B1 6

Measurements have also been made of composite sheets made from the same starting tissue but made by Vetrotex as described in Norwegian patent application NO 984275. The E-module for this material was 7-8 GPa.

5

Why the composite panels according to the invention have twice as much strength as hitherto composite plates have not been elucidated in detail, but the arguments given above for the influence of temperature, heating method, pressure and process speed indicate that the very elevated stiffness is a result of a combination of these factors, 10 where pressing with a roller at hot roll temperature is critical to the process.

In a further embodiment, the invention is characterized in that the heating process comprises heating with heat radiation. This is an option that can be used in this embodiment. However, it has been found that this step can be avoided.

In a further embodiment, the invention is characterized in that the heating with heat radiation provides a temperature of the tissue between 110 ° C and 170 ° C, preferably between 120 ° C and 160 ° C, and most preferably 140 ° C. If preheating is used, this temperature has proved advantageous. It is important, however, that in heat radiation treatment not so much heat be applied to the surface of the tissue as to break down. Generally, it is not necessary to use preheating of the tissue, however, it is not excluded that in some cases an advantage of heating can be obtained despite hot pressing rollers.

In a further embodiment, the invention is characterized in that, during the pressing process, the fabric is subjected to a roll pressure only if the thickness of the composite sheet is above a minimum adjustable thickness. The minimum thickness is adjusted to an appropriate value, taking into account the thickness of the tissue and the number of tissues that are melted and compressed.

In a further embodiment, the invention is characterized in that the tissue is subjected to cold rolling pressure by at least one rotating cold roll during the cooling process. After the first step of pressing where the composite sheet is formed with the fabric as the starting material, DK 173918 B1 7 can advantageously use one or more subsequent pressing steps, where the corresponding rollers have a much lower temperature than the hot roll temperature. During this process, the composite sheet that has not yet cured can be formed according to predetermined profiles. For example, the plate may be imparted to a wavy or molded shape depending on the end product desired. Thus, the cold rollers must be designed appropriately for the particular purposes.

In a further embodiment, the invention is characterized in that the web is subjected to a structuring of the surface during the hot pressing process and / or by pressing during the cooling process. Such a structuring of the tissue can, for example

are made by the cold rollers if their surface is formed with the structure which N

after the pressure is transferred to the surface of the composite plate. The tissue itself may be provided with holes of different shape, which complements a specific structure of the tissue.

An apparatus for making composite sheets comprising one or more means for feeding at least one matrix of threads, preferably a polymeric and glass yarn web, at least one die heating element, at least one heated rotating roller over which the die is passed, and which rotating roller is heated to a hot rolling temperature which is above the melting point of that of the materials in the matrix having the lowest melting point and below the melting point of the material having the highest melting point and wherein the hot rolling temperature is below the decomposition temperature of any of the materials, at least one device for compressing the matrix, and at least one device for cooling the matrix is characterized in that the device for compressing the matrix comprises at least one rotating hot roll heated to the hot rolling temperature. .

In a further embodiment, the apparatus is characterized in that the device for compressing the die comprises at least one set of two opposite rotationally rotating hot rolls having a parallel rotation axis heated to the hot rolling temperature, which hot rollers are arranged with one another. spacing, preferably adjustable, and a pressure directed against each other's axis, is adjustable stepwise, and so that the matrix, when passing between the hot rollers, is simultaneously exposed to heat and pressure.

In a further embodiment, the apparatus is characterized in that the device for compressing the die comprises at least one set of two opposite cold rolls rotating at the same surface velocity, which cold rolls have a surface temperature below the melting temperatures of the materials. included in the web, with parallel axis of rotation, which cold rollers are arranged after the hot rollers and are spaced apart, preferably adjustable, and a pressure directed against each other axis of rotation 10, preferably adjustable, so that the matrix passes through the cold rolls under additional pressure.

In a further embodiment, the apparatus is characterized in that the means for heating the die comprise at least one rotary pre-heating roller which is heated to hot rolling temperature and which is arranged before the device for compressing the die.

In a further embodiment, the apparatus is characterized in that the hot rollers have a diameter between 200 mm and 600 mm, preferably between 350 mm and 450 mm, and most preferably of 400 mm. It is advantageous that the hot rollers have a relatively large diameter, since it is then possible to allow the web to contact the surface of the roll over a large area, which leads to a thorough heating of the material. At small diameters, for example 40 mm, an unsatisfactory heating of the material is obtained such that there is a significant temperature difference between the surface of the formed composite plate and the median plane of the composite plate. In view of the fact that, by melting and pressing, the polymer must completely enclose the reinforcing wires, it is advantageous with large rollers for heating the tissue with contact heat.

In a further embodiment, the apparatus is characterized in that the hot rollers and / or cold rollers are designed as rotating bodies with a surface profile which differs from a cylindrical shape so that the resulting composite plate is fed to a shape which differs from a flat surface.

In a further embodiment, the apparatus is characterized in that the device for compressing the matrix has an adjustable minimum distance for passing the matrix through this device, which minimum distance defines a limit for compression of the composite plate.

In a further embodiment, the apparatus is characterized in that the means for heating comprise at least one station with heat radiation. In testing the invention, it has been found that heating of the tissue by heat radiation is not necessary. However, the invention is not limited to not using this form of heating, and it is not excluded that in special cases it may be advantageous to use this heating step.

Composite sheets made according to the invention can advantageously be used in complex structures where the sheets are used as a replacement for aluminum sheets. Composite sheets 15 have a better weight-to-stiffness ratio than aluminum sheets, and are far more impact-resistant. These properties are often crucial to material selection. Thus, composite sheets according to the invention can replace aluminum surfaces in the food industry, for example in refrigerators. Composite sheets are already used in refrigerated vehicles, however these composite sheets are made of a thermosetting plastic material and optionally embedded 20 glass as reinforcing material. Composite sheets made according to the invention contain thermoplastic material as well as a reinforcing material such as glass. They can be produced much faster, cheaper and can even be reshaped, thereby adapting to very specific tasks.

25 Other applications are refrigeration containers, dry cargo containers, body parts for agricultural machinery, aircraft, boat and automobile components, reinforced cabinets for the electronics industry, components for the weapons industry, components for the construction industry, such as cladding of facades and partitions, as well as components for the furniture industry.

30 DK 173918 B1 10

Example The table below lists various parameters used in a manufacturing method according to the invention of composite sheets from a fabric consisting of 60% glass fibers and 40% polypropylene fibers (PP).

5 ______

Ex. Plate- Roll pressure for Roll pressure foi Hot roll- Cold roll- Process- Temperature at thickness heat rolls cold rolls temperature Tj temperature T2 speed preheating [mm] Pj [N / mm] P2 [N / mm] [m / min] [° £] ~ ! 0 ^ 8 (flag) 20 50 190 4 (Γ Γ, 5m / mhT Ϊ35 2 1.5 (2 layers) _20__20___ 214 "~ 40 0.6 m / min_ 140 3 1.6 (2 layers) 20 20 220 40 2 m / min No preheating ~ T ~ 1.65 (2 layers) 20 20 214 40 ~ 1.4 m / min 140

For some of the tissues, preheating was used, which, however, did not appear to be necessary for the actual tissue. As can be seen from Example 3 of the table, it was even possible to increase the process speed when no preheating was used. In this case, it was not necessary to use higher pressures, however, the temperature was close to the decomposition temperature of the tissue, which is about 220 ° C.

In addition to the parameters listed in the table, tests with varying pressures between 20 N / mm and 600 N / mm have been performed for the hot rollers and for the cold rollers. However, 20 N / mm 15 has proved to be a very appropriate value.

The invention is explained in more detail below with reference to the drawing, in which FIG. 1 is a sketch of an apparatus for the manufacturing method according to the invention, FIG. 2 is another embodiment of an apparatus according to the invention, FIG. 3 shows various embodiments of roll profiles and FIG. 4 is a third embodiment of an apparatus according to the invention.

FIG. 1 is a sketch of an apparatus for use in the practice of the manufacturing method of the invention. The web 1, which is a long fiber composite, for example a woven or stitched matrix of polypropylene fibers and glass fibers, is conveyed from a roll 2 to a hot roll 3 heated to a hot roll temperature T1, the hot roll temperature T1 being a temperature above the melting point. for that of the materials having the lowest melting point and below the melting point of the material having the highest melting point, and where the hot rolling temperature is below the decomposition temperature of any of the materials. During contact 4 with the hot roll 3, the web 1 is heated above the melting temperature of one or more of the composite materials, after which the web under pressure PI of the roll, typically against another hot roll 3 ', is formed into a partially melted 5 composite web 5. Optionally, a second set of rollers is used. 6 and 6 ', which are cold rolls, for further pressing with pressure P2 and forming the composite web 5, 7. The cold rolls have a temperature T2 which is considerably below the hot rolling temperature T1, for example at room temperature. The cooling of the composite web 5, 7 can take place during this second pressing as well as by a further active cooling thereafter; or cooling may take place by passive cooling, that is, by heat release of the composite web to the surroundings.

In FIG. 1, two webs of webs 1 and P are shown which are compressed into one composite web.

Only one track can be used. By using two webs of a certain thickness and 15 which are fused in place of one web of double thickness, a better heating of the webs is obtained before pressing. Alternatively, a greater number of tissues may be compressed, possibly with multiple pressing steps in a more complex shaped apparatus.

FIG. 2 is another embodiment of an apparatus according to the invention using a hot roll 3 and a pre-heat roll 8 for heating the tissue 1 to the hot roll temperature. The preheating roller has a temperature TO which may be equal to or different from the hot rolling temperature. The contact surface 4 with the hot rollers thereby becomes larger, which ensures a heating of the tissue before pressing with pressure P1. Especially for thicker tissue 1, this is a great advantage. Between the preheat roller 8 and the hot roller 3, the fabric is also subjected to pressure of a variable P0 which is variable.

Should it prove necessary, it is possible to use several hot rollers in succession. The different hot rollers may have the same or different temperature. Furthermore, the tissue between the individual rollers is subjected to pressure of varying strength. An apparatus according to the invention can thereby be designed in different ways depending on the desired process steps.

DK 173918 B1 12

The speeds of rotation of the rolls, wO, wO ', wl, wl', w2 and w2 'are mutually adapted to the diameters of the rolls 3, 3', 6, 6 'so that the tissue is not exposed to an undue stretch but is nevertheless transported through the apparatus in an extended state.

5 FIG. 1 also shows other means 9 for heating the tissue 1. These are made up of heat units with heat radiation. Such heating units 9 will in most cases not be needed, as the heating ffa the hot rollers is sufficient. However, in some cases it may prove useful to heat the tissue first in this heating unit.

10 In FIG. 3, different profiles of the rollers are shown in the direction perpendicular to the rollers 6, 6 'axis of rotation 10, 10'. The rollers are arranged opposite to each other with a certain minimum spacing 11 which is adjustable depending on the thickness of the tissue. Furthermore, the rollers may be provided with a surface structure which is transferred to the web during pressing.

15 (FIG. 4) During the formation of the composite web, the web 1 may also be covered by a surface layer 12, 12 ', for example a smooth plastic web, a metal web or other, as outlined in FIG. 4. This surface web 12 will typically be applied between the hot rollers 3, 3 'and the cold rolls 6, 6'. In order for the surface web 12, 12 'together with the molten composite web 5 to form the finished composite web 7, the surface web 12, 12' is added while the composite web 5 is not yet cured. It is also possible to heat the cold rolls 6, 6 'to a temperature such that the surface web 12, 12' is heated prior to contact with the composite web 5. Alternatively, heating with heat rays 13 for the surface web 12, 12 'can be used.

25

Claims (18)

A method of making composite sheets wherein a web comprising at least two materials is passed over at least one rotating hot roll heated to a hot rolling temperature above the melting point of that of the materials having the lowest melting point. and below the melting point of the material having the highest melting point, and wherein the hot rolling temperature is below the degradation temperature of any of the materials, the fabric undergoes a heating process, a hot state pressing process and a cooling process to form a composite web, characterized by in the pressing process, the tissue is subjected to hot rolling pressure by at least one rotating hot roll heated to the hot rolling temperature. A method according to claim 1, characterized in that the web comprises yarns of polymer, preferably PP, PET or PTFE, as well as yarns of a reinforcing material, preferably glass fibers. Method according to claim 1 or 2, characterized in that the proportion of glass wires in the tissue is between 55% and 75%, preferably between 60% and 70%, and most preferably 60%. Process according to any one of the preceding claims, characterized in that the hot rolling temperature is between 0 ° - 20 ° below the decomposition temperature of the material having the lowest decomposition temperature, preferably between 0 ° and 10 ° below the decomposition temperature and most preferably between 0 ° and 6 ° below the decomposition temperature. 25 Method according to any one of the preceding claims, characterized in that the hot rolling pressure is between 10 N / mm and 50 N / mm, preferably between 20 N / mm and 40 N / mm, and most preferably 30 N / mm. DK 173918 B1 Process according to any one of the preceding claims, characterized in that the process speed is between 0.5 m / min and 2 m / min, preferably between 1.4 and 1.6 m / min. A method according to any one of the preceding claims, characterized in that the heat transfer to the tissue by heat transfer from at least one hot roll to the tissue upon contact of the tissue with the hot roll is between 80% and 100%. preferably 100%, of the total heat supply during the heating process. 10 Process according to any of the preceding claims, characterized in that the heating process comprises heating with heat radiation. Method according to claim 7, characterized in that the heating with var radiation is a temperature of the tissue between 110 ° C and 170 ° C, preferably between 120 ° C and 160 ° C, and most preferably 140 ° C. Method according to any one of the preceding claims, characterized in that the web is subjected to a roll pressure during the pressing process only if the thickness of the composite plate is above a minimum adjustable thickness. Method according to any of the preceding claims, characterized in that the tissue is subjected to cold rolling pressure 25 by at least one rotating cold roll during the cooling process. Method according to any one of the preceding claims, characterized in that the web is subjected to a structuring of the surface during the hot pressing process and / or by pressing during the cooling process. Apparatus for making composite sheets comprising DK 173918 B1 - one or more means for supplying at least one matrix of threads, preferably a polymeric and glass filamentous tissue, - at least one die heating element, - at least one heated rotating roller over which the die is passed and the rotating roller is heated to a hot rolling temperature which is above the melting point of the material having the lowest melting point and below the melting point of the material having the highest melting point and where the hot rolling temperature at least one device for compressing the die, and 10. at least one device for cooling the die, characterized in that the device for compressing the die comprises at least one rotating hot roll heated to the hot roll temperature. . Apparatus according to claim 12, characterized in that the device for compression 15 of the matrix comprises at least one set of two opposite rotationally rotating hot rolls having a parallel rotation axis heated to the hot rolling temperature, which hot rollers are arranged with one another. distance, preferably adjustable, and a pressure directed at each other's axis of rotation, preferably adjustable, and so that the matrix, when passing between the hot rollers, is simultaneously exposed to heat and pressure. Apparatus according to claim 13 or 14, characterized in that the device for compressing the die comprises at least one set of two opposite rolls rotating at the same surface velocity, which cold rolls have a surface temperature below the melting temperatures of the materials. which are included in the web with parallel axis of rotation, which cold rollers are arranged after the hot rollers and are spaced apart, preferably adjustable, and a pressure directed against each other axis, preferably adjustable, so that the matrix passes through the cold rolls under additional pressure. 30 DK 173918 B1 Apparatus according to claims 13-15, characterized in that the means for heating the die comprise at least one rotary pre-heating roll which is heated to hot roll temperature and which is arranged before the device for compressing the die. Apparatus according to claims 13-16, characterized in that hot rollers have a diameter between 300 mm and 500 mm, preferably between 350 mm and 450 mm, and most preferably of 400 mm. Apparatus according to claims 13-17, characterized in that the hot rollers and / or cold rollers are designed as rotating bodies with a surface profile which differs from a cylindrical shape so that the resulting composite plate is fed to a shape which differs from a flat surface. . Apparatus according to Claims 13 to 18, characterized in that the device for compressing the matrix has an adjustable minimum distance for passing the matrix through this device, which minimum distance defines a limit for compression of the composition plate. Apparatus according to claims 13 - 18, characterized in that the means for heating 20 comprise at least one station with heat radiation.