EP0966001A1 - Manufacture of a mica tape and obtained product - Google Patents

Abstract

The invention concerns a method for making a micaceous product capable of being impregnated preferably in the form of a mica ribbon by combining at least a support and a mica sheet. The invention is characterised in that it consists in: coating the support and the sheet with a solvent-free resin or a mixture of solvent-free resins using several coating rollers brought to a temperature for producing the coat; combining the support with the mica sheet; subjecting them to a pressure and heat treatment.

Description

Subject of the invention

The present invention relates to the production of a micaceous product preferably presented in the form of a mica tape comprising a support coated with a solvent-free resin combined with a sheet of mica.

The present invention also relates to a new micaceous product.

Technological background underlying the invention

The micaceous ribbons are presented under the form of a support impregnated with a resin, for example epoxy, combined with a sheet of mica. This mica sheet can be mica paper, possibly reinforced with a small amount of resin, for example epoxy.

To make such ribbons, we know the "pistolage" technique (also called in English "spraying") which consists of spreading and impregnating a paper mica of an epoxy resin in a solvent medium and then associate it with a support.

On the other hand, it is also known to use solid resin powdering techniques either on a sheet of mica or directly on the support, and then to join the two elements together pressure and heat action. In particular, the publication EP-A-0194974 describes a preparation process thin mica tapes suitable for impregnation and comprising an incorporated accelerator, characterized in that one sprinkle a thin sheet of mica with a powder varnish free of hardener, then either glue the side of the sheet of fine mica sprinkled with varnish by an action of pressure or heat with a glass cloth or felt serving as a support, or a glass cloth is impregnated with a liquid accelerator or solution of an accelerator liquid or solid in a low boiling solvent and we glue the support thus obtained by an action of pressure and heat with one side of the mica sheet sprinkled with varnish, and then we impregnate the laminate obtained with a liquid accelerator or a solution of liquid or solid accelerator in a low point solvent of boiling. Another possibility is to impregnate a mica sheet with a liquid accelerator or a solution of a liquid or solid accelerator in a solvent with low boiling point, then sprinkle with hardener-free powder varnish mica sheet impregnated, and then either to impregnate a glass cloth a liquid accelerator or a solution of a liquid or solid accelerator in a low point solvent of boiling by sticking the support thus obtained by a action of heat and pressure with the side of the sheet of fine mica sprinkled with powder varnish, either to stick the felt serving as support by an action of pressure and heat with the side of the fine mica sheet sprinkled with powder varnish. We observe however that by using this process, the sprinkling of a varnish requires the use of a certain amount of it. In particular, the varnish will tend when sprinkled on the support, to pass through the meshes and to be found on both sides of the support.

Aims of the invention

The present invention aims to provide a technique which avoids the use of solvents for the preparation of micaceous products such as ribbons of mica.

The present invention also aims to allow the production of flexible ribbons increased while having sufficient adhesion qualities or even increased.

Furthermore, the present invention aims to propose, in the particular case of the realization of coiled ribbons, a process which avoids the problem of bonding between successive turns.

The present invention also aims to propose a manufacturing process for micaceous products suitable for impregnation which requires the use of a low resin content.

Main characteristic features of the invention

• on effectue une enduction sans solvant d'une résine sur le support ou sur la feuille de mica à l'aide de cylindres d'enduction à une température de mise en oeuvre de l'enduction,
• on associe le support à la feuille de mica, et
• on les soumet à un traitement de pression et de température à une seconde température de mise en oeuvre.

The present invention relates first of all to a process for producing a micaceous product, preferably in the form of a mica tape obtained by combining a support and a mica sheet, characterized in that :

• a solvent-free coating of a resin is carried out on the support or on the mica sheet using coating rolls at a temperature for applying the coating,
• we associate the support with the mica sheet, and
• they are subjected to a pressure and temperature treatment at a second operating temperature.

By "processing temperature of coating ", it’s important to understand the temperature at which is worn the solvent-free resin mixture so to be able to coat the support or the mica sheet. This temperature is usually between 40 and 200 ° C. This means that the resin must be present under a non-solid form, that is to say in a more or less state viscous or liquid.

By "pressure and temperature "means a treatment at a temperature between 40 and 200 ° C for a pressure included between 0 and 20 bars to allow the connection of the support with mica sheet.

Among the possible examples of resin intended for coating, there may be mentioned resins without solvent or silicone adhesives and all resins without solvent with adequate viscosity at temperatures of implementation of the coating.

The medium can be either a film or fabric, or even a felt. The mica sheet is preferably a classic mica paper made according to usual stationery techniques. This mica paper can be 100% mica paper or possibly mica paper previously reinforced with resin impregnation, for example epoxy, by a setting process in conventional work such as impregnation by coating in solvent medium.

We can consider incorporating a accelerator either to the resin used for coating, either during a preliminary stage during the preparation of the mica sheet in the so-called impregnation resin, or still directly on the support or on the mica sheet herself.

In the first forms of execution, the accelerator is then directly mixed with the resin.

In general, we can consider to use an accelerator in the form of a nitrogen compound such as an amine or a compound organometallic such as Zinc Naphtenate, or any other compound having the desired catalytic effect.

A second object of the present invention is relates to micaceous products preferably presented in the form of a mica tape and comprising on the one hand a support impregnated by solvent-free coating of a resin and a sheet of mica, or a sheet of mica impregnated by solvent-free coating of a resin and the support itself, these two elements being secured.

We observe that in the case where the support is a fabric, there will be resin deposits only on the intersections of the weft threads with those of the warp. More specifically, we will observe traces of resin only at intersections where the weft thread is superimposed on that of the chain. This allows to obtain particularly advantageous very precise adjustment the resin content on the finished ribbon, and the rate resin is significantly lower than for products obtained by the processes of the state of the art (spraying or using a solid powder). this allows furthermore to preserve or even increase flexibility characteristics and limit the risks of bonding between turns when the ribbon is wound.

Preferably, the fabric will be a woven glass fiber fabric or silk, having a grammage of 20 to 50 g / m ² . The mica sheet, and preferably the mica paper, has a basis weight between 100 and 250 g / m ² .

Brief description of the figures

Figure 1

represents a schematic view of the device intended to carry out the coating process according to the present invention.

Figure 2

represents a schematic view of the second step in the process of making a ribbon micaceous according to the present invention, which consists in securing the support to the paper mica.

Figure 3

represents a schematic description of a glass fabric impregnated by the technique described.

Description of several preferred embodiments of the invention

Figure 1 shows a schematic view of a device intended to carry out the method according to the invention. This device comprises on the one hand a station of coating consisting essentially of several successive cylinders, and preferably four cylinders (1, 2, 3 and 4), which allow the coating of a very low amount of resin on the support.

This coating unit is followed by a laminating unit which brings the two elements, i.e. the mica sheet and the support, in contact, and which exerts on the whole an action of pressure and temperature as described in figure 2. This action pressure is carried out using two cylinders (5 and 6). Preferably, only one of the two cylinders will be heated.

The following examples describe more specific two examples of carrying out the process according to the present invention.

Examples Example 1

1) Une résine époxyde non modifiée à base de bisphénol A et d'épichlorhydrine. Il s'agit d'une résine solide à température ambiante et exempte de solvant. Cette résine a un poids équivalent époxyde compris entre 350 et 400 g/équiv. et une viscosité à 90 °C de l'ordre de 4000 mPa.s.

2) Un tissu de verre de grammage de 24 g/m² constitué de 26 fils/cm en chaíne et de 15 fils/cm en trame, le titre des fils étant de 5,5 tex en chaíne et en trame.

3) Un papier mica de type Muscovite de grammage de 160 g/m², préalablement renforcé avec 4 g/m² de résine époxyde additionnée d'un accélérateur de type sel métallique. L'adjonction de la résine époxyde et de l'accélérateur au papier mica étant réalisé de manière classique c'est-à-dire par imprégnation en milieu solvant.

Pour réaliser le ruban mica on procède comme suit:

A) On préchauffe dans une étuve la résine époxyde à 90 °C. Lorsque la résine a atteint la température et est suffisamment fluide, on verse la quantité adéquate entre les cylindres 1 et 2 du stand d'enduction décrit à la figure 1. Les cylindres 1 et 3 du stand d'enduction ont été préchauffés à 90 °C et sont maintenus à cette température pendant tout la durée de l'enduction. On règle les vitesses de rotation et les écartement entre les différents cylindres du stand d'enduction afin d'obtenir le transfert d'une fine couche de résine du cylindre 2 au cylindre 3 et du cylindre 3 au cylindre 4.

B) On déroule le tissu de verre et on l'amène en contact tangentiel avec le cylindre 4 du stand d'enduction comme décrit à la figure 1. Le tissu de verre entraíne une partie de la résine se trouvant sur le cylindre 4.

C) D'autre part, on déroule le papier mica et on vient le mettre en contact au niveau de l'unité de contre-collage décrite à la figure 2 avec le tissu de verre enduit. Le cylindre 5 a été préchauffé à 80 °C. On effectue une pression de 20 bars du cylindre 6 sur le cylindre 5 de façon à solidariser le papier mica sur le support afin d'obtenir un ruban micacé.

D) On enroule le ruban micacé ainsi obtenu.

A ribbon of mica is produced by hot coating of a glass fabric support using a solvent-free resin and the coated support is laminated on a mica paper. For this, the following materials are used:

1) An unmodified epoxy resin based on bisphenol A and epichlorohydrin. It is a solid resin at room temperature and free of solvent. This resin has an epoxy equivalent weight of between 350 and 400 g / equiv. and a viscosity at 90 ° C of the order of 4000 mPa.s.

2) A glass fabric of grammage of 24 g / m ² consisting of 26 threads / cm in warp and 15 threads / cm in weft, the title of the threads being 5.5 tex in warp and weft.

3) A Muscovite type mica paper with a grammage of 160 g / m ² , previously reinforced with 4 g / m ² of epoxy resin added with an accelerator of the metal salt type. The addition of the epoxy resin and the accelerator to the mica paper being carried out in a conventional manner, that is to say by impregnation in a solvent medium.

To make the mica tape we proceed as follows:

A) The epoxy resin is preheated in an oven to 90 ° C. When the resin has reached the temperature and is sufficiently fluid, the appropriate quantity is poured between the cylinders 1 and 2 of the coating stand described in FIG. 1. The cylinders 1 and 3 of the coating stand have been preheated to 90 ° C and are maintained at this temperature for the duration of the coating. The speeds of rotation and the spacing between the different cylinders of the coating stand are adjusted in order to obtain the transfer of a thin layer of resin from cylinder 2 to cylinder 3 and from cylinder 3 to cylinder 4.

B) The glass fabric is unrolled and brought into tangential contact with the cylinder 4 of the coating stand as described in FIG. 1. The glass fabric entrains part of the resin located on the cylinder 4.

C) On the other hand, the mica paper is unwound and it is brought into contact at the level of the laminating unit described in FIG. 2 with the coated glass fabric. Cylinder 5 was preheated to 80 ° C. A pressure of 20 bars is applied from cylinder 6 to cylinder 5 so as to secure the mica paper to the support in order to obtain a micaceous ribbon.

D) The micaceous ribbon thus obtained is wound up.

With the settings used in the example, a deposit of the order of 5 g / m ² of epoxy resin is obtained on the glass fabric. If we observe a binocular or microscope sample of coated glass fabric as described above, we see the presence of resin only at the intersections between the warp threads and the weft threads and more precisely only at the intersection where the weft son is superimposed on the warp son, that is to say at an intersection on 2 as described in Figure 3. We also see that there is no transfer of resin on the other face of the glass cloth.

The characteristics of a mica tape as well performed (ribbon A) are shown in Table I and compared with those of a ribbon made by the classical technique called spraying in solvent medium (ribbon B). We observe that ribbon A manufactured according to the process described above contains resin content below the rate normally required for a ribbon B manufactured by the classic spraying technique in solvent medium. Of more, tape A has better flexibility, more high porosity and better tensile strength than tape B. Tape A is also completely dry on the outside of the glass fabric since the resin is only located at the interface between the fabric of glass and mica paper, this characteristic limits the risks of sticking between turns of the wound ribbon.

Example 2

1) Une résine époxyde non modifiée à base de bisphénol A et d'épichlorhydrine. Il s'agit d'une résine liquide de haute viscosité à température ambiante et exempte de solvant. Cette résine a un poids équivalent époxyde compris entre 235 et 265 g/équiv. et une viscosité à 90 °C de l'ordre de 300 mPa.s.

2) Un film polyester de 23 µm d'épaisseur

3) Un papier mica de type Muscovite de grammage de 180 g/m², préalablement renforcé avec 5 g/m² de résine époxyde par imprégnation en milieu solvant.

A mica tape is produced by hot coating using the same technique as described in Example 1. For this, the following materials are used:

1) An unmodified epoxy resin based on bisphenol A and epichlorohydrin. It is a liquid resin of high viscosity at room temperature and free of solvent. This resin has an epoxy equivalent weight of between 235 and 265 g / equiv. and a viscosity at 90 ° C of the order of 300 mPa.s.

2) A 23 µm thick polyester film

3) A Muscovite type mica paper with a basis weight of 180 g / m ² , previously reinforced with 5 g / m ² of epoxy resin by impregnation in a solvent medium.

To make the mica tape, we proceed from the same way as in example 1 by replacing the fabric of glass by polyester film.

With the settings used in the example, a deposit of the order of 4 g / m ² of epoxy resin is obtained on the polyester film. The mica tape thus produced is extremely flexible and the adhesion between the polyester film and the mica paper is very good. Characteristics Unit Ribbon A Ribbon B Weight g / m ² 189.5 198 Content of binder by loss on ignition g / m ² 9.7 14.8 Thickness mm 0.13 0.13 IEC flexibility N / m 24 30 Porosity on the mica side dry. 299 350 Support side porosity dry. 208 300 Tensile strength kg / cm 9.8 8.5 Drilling at 70 ° C dry. 30 40

Claims (15)

Process for producing a micaceous product, preferably in the form of a mica tape obtained by combining at least one support and a mica sheet, characterized in that: a resin or mixture of resins is coated without solvent on the support or on the mica sheet using several coating rollers brought to a temperature for applying the coating, we associate the support with the mica sheet, and they are subjected to a pressure and temperature treatment. Method according to claim 1, characterized in that the processing temperature of the coating is between 40 and 200 ° C. Method according to claim 1 or 2, characterized in that the pressure and temperature is between 40 and 200 ° C for a pressure between 0 and 20 bars. Method according to any one of previous claims, characterized in that incorporates an impregnating resin into the sheet mica. Method according to any one of previous claims, characterized in that the resin intended for coating is a resin having a point melting point below the processing temperature. Method according to any one of previous claims, characterized in that the resin is a solvent-free resin, preferably silicone type or epoxy. Method according to any one of previous claims, characterized in that incorporates an accelerator into the coating resin. Method according to any one of previous claims, characterized in that incorporates an accelerator into the mica sheet. Method according to any one of previous claims, characterized in that incorporates an accelerator into the support. Method according to any one of previous claims, characterized in that the accelerator is a nitrogen compound, a compound organometallic. Method according to any one of previous claims, characterized in that the support may be a film, a fabric or a felt. Method according to any one of previous claims, characterized in that the mica sheet is preferably mica paper previously reinforced with resin impregnation. Method according to any one of previous claims, characterized in that the mica sheet is made from calcined muscovite or not, phlogopite, vermiculite or mica synthetic or a combination thereof. Micaceous product presenting preferably in the form of a mica tape comprising a support coated with a solvent-free resin associated with a mica sheet. Micaceous product according to claim 14, characterized in that the support is a fabric on which resin deposits only appear on the wires from the frame to the intersection with the warp threads.

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