SE505843C2 - Composite material prodn. - Google Patents

Abstract

Method uses a web impregnated with curable resin and expandable thermoplastic microspheres in a solvent carrier. The impregnated web is overlaid by a porous material and is hot pressed which causes curing, microsphere expansion, and solvent removal to take place simultaneously. The solvent escapes by passing through the porous material. Web is pref. of glass fibre or polyester fibre. The web is conventionally impregnated with a mixture consisting of unexpanded microspheres of any suitable thermoplastic, dispersed in a soln. of a curable resin, such as phenolic resin in aqueous soln. of 50% solids. Microsphere content is pref. such as to form 75-90% by volume of the finished composite. A sheet of porous material is placed over one or both sides of the impregnated web and the assembly is placed in a hot press, typically at 140 deg.C. The porous material allows solvent emission during pressing and allows partial penetration by the resin mixture. Suitable porous materials include expanded metal, foamed plastics pref. with a density of 5-80 kg/cm3, and glass or mineral wood pref. with a density of 100-200 kg/cm3.

Description

505 845 prior art regarding the actual application of the process and / or the properties of the final product.

According to the present invention, the process is carried out in a single stage in a hot press by placing a porous material layer on one or both sides of the impregnated web material, placing the combination of the impregnated web-shaped material and said at least one porous material layer in a hot press or the like. and there is exposed to heat so that the solvent evaporates and the thermoplastic particles expand, that the material layer and the impregnated web material are formed or selected so that a partial penetration of the resin mixture into the material layer occurs when the thermoplastic particles expand, and that the solvent layer is selected caused to deviate substantially along and / or through the material layer. Thus, in accordance with the invention, it is advantageous to carry out approximately simultaneous drying (causing the solvent to evaporate) and expansion of the thermoplastic particles with directly subsequent successive curing of the curable resin.

The following is a more detailed description of the features of the method according to the invention.

The composite material can be prepared, for example, as follows: a precondensate of an aqueous curable resin is prepared in a conventional manner and the water content is controlled so as to obtain a dry content of 30 to 75% by weight. The solution thus obtained is charged with unexpanded thermoplastic particles, so-called microspheres, in such an amount that the weight ratio of microspheres: resin in the finished foam composite material varies between 4: 1 and 1:50. It is advantageous to include the microspheres in such an amount that in the expanded state they constitute 50-95, preferably 75-95, volume% of the web material and the resin mixture. The web material is impregnated with the mixture of resin and microspheres in a conventional manner, for example by immersing the web in a bath of the mixture or by spraying the mixture on the web. The degree of impregnation of the impregnated web can be regulated, for example, by pressing with rollers.

The curable resins which are preferably used are so-called formaldehyde-based resins with urea, phenol, resorcinol or melamine. However, more generally curable resins can also be used, such as polycondensed resins, for example polyimide, and polyadded resins, for example polyurethane.

The web-shaped material may consist of woven or non-woven, organic or inorganic material, mentioning in particular of glass fiber, mineral fiber, cellulose fiber and polyester fiber. It is also important that the web-shaped material has sufficient porosity to be satisfactorily impregnated with the mixture of resin and microspheres. Furthermore, the web-shaped material should not be too thick, and suitably the thickness may vary between 0.1 and 5 mm. The reason why the web-shaped material must be thin is that there is otherwise a risk of uneven expansion of the microspheres in that the peripheral microspheres at the heat supply first expand and form a heat-insulating layer, which prevents the more centrally located microspheres from expand, and in such a case a non-homogeneous product of inferior quality is obtained.

The microspheres used in the preparation of the composite material of the invention have shells, which may be copolymers of vinyl chloride and vinylidene chloride, copolymers of vinyl chloride and acrylonitrile, copolymers of vinylidene chloride and acrylonitrile, and copolymers of styrene and acrylonitrile.

Mention may also be made of copolymers of methyl methacrylate containing up to about 20% by weight; styrene, copolymers of methyl methacrylate and up to about 50% by weight of combined monomers of ethyl methacrylate, copolymers of methyl methacrylate and up to about 70% by weight of orthochlorostyrene. The particle size of the unexpanded spheres and thus of the expanded spheres can vary within wide limits and is selected on the basis of the desired properties of the finished product. Examples of particle sizes for unexpanded spheres are 1 μm to 1 mm, preferably 2 μm to 0.5 mm and especially 5 μm to 50 μm. During expansion, the diameter of the microspheres increases by a factor of 2-5. The unexpanded spheres contain volatile, liquid blowing agents, which evaporate on heat application. These blowing agents may be freons, hydrocarbons such as n-pentane, i-pentane, neopentane, butane, i-butane or other blowing agents which are conventionally employed in microspheres of the type indicated herein. 5-30% by weight of the microsphere may suitably be blowing agent. The microspheres can be added to the resin solution as dried particles or in a suspension, for example in water or an alcohol, such as methanol.

The relationship is resin to. microspheres> in the impregnation solution can, as previously stated, vary within wide limits and this ratio affects the properties of the finished product. Conversely, based on a certain area of use and certain desired properties of the finished product, a suitable ratio of resin to microspheres in the mixture can be selected. This ratio can be easily determined by laboratory scale preparatory experiments.

The mixture of resin and microspheres can, if desired or required, be supplemented with various additives, such as stabilizers, couplers, fillers, flame retardant additives and / or pigments.

According to the invention, a porous material layer is applied to one or both sides of the web-shaped material impregnated with the resin mixture. This means that said porous material layers could be located between two material webs impregnated with the resin mixture. By the term "porous" in connection with the material layer is to be understood that this must have such openings or cavities that it partly allows a partial penetration of the resin mixture into the material layer when the thermoplastic particles expand, and partly allows solvent to escape along and / or through the material layer. In practice, the material layer may consist of some form of fibrous layer or fibrous web, for example of a woven or nonwoven, organic or inorganic fibrous material.

The term "fibrous web" here includes so-called fiber, chip or chip mats, for example of glass or mineral.

Examples of fibrous materials are glass fiber, mineral fiber, cellulose fiber and polyester fiber. Particularly advantageous alternatives in this respect are to design the porous layer of glass wool or mineral wool.

Alternatively, the porous material layer can also consist of so-called expanded metal, namely a necrotic metal structure formed by a single continuous piece of metal. In such expanded metal there are connecting bridges which are more or less inclined in relation to the main plane of the expanded metal layer. Within such bridges, the expanded metal layer has through-openings.

Thus, the expanded metal layer allows solvent to escape through the expanded metal layer. openings 'and' further, the solvent may escape in parallel with the expanded metal layer due to the openings and cavities present in connection with the expanded metal layer.

An additional alternative to material layers is a foam layer, for example of melamine foam or polyester foam. Such a foam layer can, when performing the process, be placed on one side of the impregnated web-shaped material in order to provide the intended composite material. One. such a foam layer. could also be placed between layers formed by the impregnated web-shaped material. as foam plastic, a foam plastic with a relatively soft character is advantageously selected. The density of the foam can be chosen, for example, to about 200 kg / m3 or less. Though. the density of the foam should preferably be chosen to about 5 kg / m3 or more. Particularly favorable 505,843 results have been obtained with foams, the densities of which were between 5 and 80 kg per m3.

When using glass wool or mineral wool for the porous material layer, the density is advantageously chosen to be somewhere between 50 and 300 kg / m 3, with between 100 and 200 kg / ms being especially preferred.

The combination of the impregnated web material and said porous metal layer is placed in a hot press or the like and exposed there to heat so that the solvent evaporates and the thermoplastic particles expand.

The material layer and the impregnated web-shaped material are designed or selected so that a partial penetration of the resin mixture into the material layer takes place when the thermoplastic particles expand. Thus, a noble coupling occurs between the resin mixture, the web-shaped material and the porous material layer. As already mentioned, the material layer is selected of such a porous nature that the solvent can substantially escape along and / or through the material layer. In a normal press construction, the solvent largely escapes to the sides through the part of the porous material layer which is not absorbed by the penetrated resin mixture.

The curing of the curable resin takes place at the same stage in the hot press as the solvent evaporation and expansion of the thermoplastic particles, the timing may suitably be such that the solvent evaporation and the expansion of the thermoplastic particles take place approximately simultaneously while the curing of the curable resin takes place at that temperature increase. which occurs when significant volumes of solvent have passed. Optionally, the expansion of the thermoplastic particles can also take place before the solvent evaporation, which is followed by the curing of the curable resin. 505 843 The combination of the impregnated web-shaped material and the porous material layer or layers is suitably placed in the hot press which is then closed to a certain given gap width. The subsequent expansion of the thermoplastic particles gives rise to such a volume increase that the pressing surfaces create a pressing function without the pressing surfaces having to approach each other.

The curable resin is thus caused to change in one step from A-stage to C-stage, i.e. no semi-finished product of the composite material with the curable resin in B-stage occurs.

The impregnation of the web-shaped material with the resin mixture and the subsequent hot pressing can be done at significant time intervals or substantially completely unrelated to each other so that the web-shaped impregnated material acquires the character of a semi-finished product. Such a semi-finished product may, for example, have, in a condition where the solvent is substantially undried, a somewhat moist character. In any case, in the semi-finished product, the thermoplastic particles are substantially unexpanded and the curable resin is in substantially A-stage. Although it is normally preferred that this semi-finished product is not subjected to any drying operation in any heating device, drying chamber or the like suitable for the purpose, it would in itself be possible to also carry out such drying or solvent evaporation.

However, this should not be driven further than that, as mentioned, the thermoplastic particles are substantially unexpanded and the curable resin is in substantially A-stage.

This semi-finished product can at a later time be used in a hot press or the like together with the porous material layer in order to carry out expansion of the thermoplastic particles, solvent evaporation and curing of the curable resin to C-stage. 505 845 It should be emphasized that regardless of whether such semi-finished products are used, in which partial solvent escape has already been provided, or if no solvent escape has yet taken place, it is according to the invention in the heat treatment or hot pressing itself that in a single treatment or pressing operation the evaporation of at least a significant part of the solvent, the expansion of the thermoplastic particles and the curing of the resin are carried out, in this operation the curable resin passes directly from A-stage to C-stage.

The temperature in the heating device, the hot press or the like during the treatment of the composite material can vary between 100 and 200 ° C, preferably 120-160 ° C. In experiments, good results have been obtained at about 140 ° C.

As already mentioned, an essential task for the porous material layer is to function so that the solvent can escape along and / through the material layer. In addition, the porous material layer usually also has additional functions. More specifically, it can simply function as a distance-forming layer in various sandwich-like composite materials, and this regardless of whether there are layers obtained from the impregnated web-shaped material on either side of it or only on one side thereof. The porous material layer may also have the character of inexpensive filler material.

In a particularly preferred embodiment according to the invention, in which impregnated webs of material are placed on either side of a porous material layer, the porous material layer, the impregnated web-shaped material and the heating and pressing conditions are selected so that the curable resin and / or thermoplastic forms connecting bridges through it. porous material layer. In such an embodiment, however, the connecting bridges must not become so extensive that they prevent solvent degassing along and / or through the material layer.

Such connecting bridges between the layers obtained on either side of the porous material layer, obtained from the impregnated, web-shaped 505 843 material, imply a more stable interconnection between the latter layers than that which could be provided by the porous material layer alone. In this way, improved strength properties are achieved, for example in terms of rigidity of the obtained composite material, but above all in terms of resistance to splitting of the composite along the porous material layer. Especially with per se well-compressible, porous material layers, the connecting bridges also mean a greater resistance to compression of the porous material layer. The connecting bridges are particularly advantageous in such cases where the porous material layer consists of foam plastic or otherwise material which is relatively soft or has a low density but where, despite such softness or low density, one wishes to achieve good strength properties.

The following are non-limiting examples of the preparation of composite materials according to the invention: EXAMPLE 1 To a formaldehyde-based resin (for example melamine, phenol) in aqueous solution with 50% dry matter content, expanded 'thermoplastic particles are added to achieve a' dry matter content of 15%. %. A web-shaped material in the form of a fibrous web is impregnated with the mixture.

A glass fiber mat or a expanded metal layer is placed on one or both sides of the impregnated fiber web. The combination is placed in a hot press with, for example, a temperature of 140 ° C with a given gap. As the thermoplastic particles expand, a partial penetration of the resin mixture into the fiberglass mat or expanded metal layer occurs. The water leaves for the most part to the sides through the part of the fiberglass mat or expanded metal layer which is not filled by the resin mixture.

Thus, approximately simultaneous drying and expansion takes place with directly subsequent successive curing of the curable resin. By "given gap" is meant that the gap of the press does not change during the pressing function itself. Instead, the pressing function arises as a result of the expansion of the thermoplastic particles. The material between the pressing surfaces will thus expand to such an extent that a pressing function arises between the pressing surfaces. It follows that the starting gap width must be adapted to the expansion of the thermoplastic particles.

EššBQšl_Z A hot press was placed on either side of a porous material layer consisting of polyether foam with a thickness of 5 mm and a density of 30 kg / m3 with a mixture of curable resin in a solvent and unexpanded thermoplastic particles impregnated mats, whose dry weight was 350 g / m2. These impregnated mats included 100 g / m2 of fiberglass chips on the sides facing the foam layer.

After pressing, a sheet-shaped product was obtained with a thickness of 4 mm and with hard surfaces and high rigidity. The basis weight was 850 g / m2. The surface mats, which consisted of fiberglass, were partially connected to each other by means of connecting bridges extending through the foam plastic layer located therebetween. These connecting bridges passed. of a mixture of the curable resin and the thermoplastic.

EK§m2šl_å In a hot press, a glass fiber mat with a basis weight (dry weight) of 350 g / m2 and a glass chip mat with a basis weight of 50 gmz was placed with a mixture of a curable resin in a solvent and unexpanded thermoplastic particles. After pressing, one was obtained. hard and rigid board product, in which the resin mixture partially penetrates the glass chip mat. With a suitable choice of mat thicknesses and impregnation conditions as well as pressing conditions, it is achieved that the resin mixture in some cases penetrates completely through the glass chip mat.

ExQmDeLA The procedure is the same as in Example 3, except that glass chip mats with a basis weight of 50 g / mz are applied to both sides of the impregnated fiberglass mat. Consequently, the glass chip mats will form surface layers on both sides of the board product together with resin mixture penetrated therein.

In a hot press, a fiberglass mat with a basis weight of 350 g / m 2 and impregnated with a mixture of a curable resin in a solvent and unexpanded thermoplastic particles and a mineral wool layer with a thickness of 15 mm and a density of 150 kg / m 3 were placed. When pressing, the resin mixture penetrates 1-2 mm into the mineral wool so that an intimate adhesion occurs.

The procedure was the same as in Example 5 except that impregnated fiberglass mats were placed on both sides of the mineral wool layer.

The process according to the invention is of course not only limited to the examples given here. In order to illustrate this, it may be mentioned that the process by means of a suitable choice of material in the porous material layer and the impregnated web-shaped material as well as a suitable choice of the heat treatment or hot pressing conditions could mean that solvent escape could take place during a significant part of the process. and / or through the porous material layer but that in the final stage of the manufacturing process the resin mixture would penetrate almost completely into the porous material layer that it would no longer give a porous impression but instead be substantially filled with the resin mixture, which would also be present on the surface of the originally porous material layer, whether this surface was located at the extreme to the surroundings or formed an interface with an additional layer included in the composite material. Further modifications are also possible within the scope of the inventive concept.

Claims (13)

505 843 13 Eatentkrgv A process for producing a composite material, comprising impregnating a web-shaped material with a mixture of a curable resin in a solvent and unexpanded thermoplastic particles, after which the impregnated web-shaped material is subjected to heat in order to expand the thermoplastic particles. and curing of the resin, characterized in that a porous material is placed on one or both sides of the impregnated web material. material layer, that the combination of the impregnated web-shaped material and said at least one material layer is placed in a hot press or the like and exposed to heat so that the solvent evaporates and the thermoplastic particles expand, that the material layer and the impregnated web-shaped material are formed or selected so that a at least partial penetration of the resin mixture into the material layer takes place and thus a joint. between the material layer. and the web-shaped material is achieved, and that the material layer is selected so that the solvent is caused to escape substantially along and / or through the material layer. 2. A method according to claim 1, characterized in that the web-shaped material consists of a woven or non-woven, organic or inorganic fibrous material. 3. A method according to claim 1 or 2, characterized in that the material layer consists of foam plastic. 4. A method according to claim 3, characterized in that the density of the foam is selected to be about 200 kg / m 3 or less. 505 843 14 5. A method according to claim 3 or 4, characterized in that the density of the foam is selected to be about 5 kg / m 3 or more. 6. A method according to claim 3, characterized in that the density of the foam is selected to be 5-80 kg / m 3. 7. A method according to claim 1 or 2, characterized in that the material layer consists of a woven or nonwoven, organic or inorganic fibrous material. 8. A method according to claim 1 or 2, characterized in that the material layer consists of expanded metal. 9. A method according to claim 1, characterized in that the web material is prepared as a semi-finished product by impregnation with the resin mixture and that in this semi-finished product the thermoplastic particles are substantially unexpanded and the curable resin in substantially A-stage. 10. A method according to claim 1, characterized in that the evaporation of the solvent, the expansion of the thermoplastic particles and the curing of the resin are carried out in one and the same hot press or the like. Process according to Claim 1 or 10, characterized in that the evaporation of the solvent is carried out approximately simultaneously with and / or before the main curing of the resin. 12. A method according to any preceding claim, characterized in that the curable resin is transferred in one step from A-stage to C-stage. A method according to any preceding claim, wherein the porous material layer is placed between uniformly impregnated material, characterized in that the material layer, the impregnated web-shaped material and the pressing conditions are selected so that the curable resin and / or thermoplastic forms connecting bridges through mats. - rial layer.