Process for preparing phenolic resin foam reinforced with glass fibres.

p0001The invention relates to a process for the preparation of, in particular of lightweight glass fiber-reinforced phenolic resin foam in which a glass fiber mat with a foamable phenolic resin solution impregnated and the phenolic resin is then foamed by application of heat under embedding of the glass fibers, wherein the solvent evaporated.

p0002Glass fiber-reinforced phenolic resin foams of this type are known. They are used in many areas and are characterized by good insulation against cold and heat, high chemical resistance and dimensional stability. Especially advantageous is the low weight and poor combustibility, making phenolic foams to an interesting material in the construction field. Because of its good thermal and toxic properties against eg polyurethane and polystyrene foam, there are also numerous applications.

p0003Phenolic resin foams have, however, drawbacks and in particular be so low wear resistance and low bending stiffness_'objected. Phenolic foams are also brittle, the application 'options significantly limits.

p0004To eliminate these disadvantages, numerous methods for the reinforcement of phenolic resin foams are known. In particular glass fiber-reinforced phenolic resin foams are used. Through the incorporation of the glass fibers in the phenolic foam flexural strength and wear resistance to be increased. For this purpose it is necessary that the glass fibers are distributed very uniformly in the phenolic foam and are embedded by this also properly and without flaws.

p0005There is a danger, that the added glass fibers are unevenly distributed in the foamable phenolic resin solution.

p0006They tend also to the solution to sink to the bottom, where local densities occur on glass fibers, which are then wetted only partially included in the phenolic resin. The phenolic resin often does not foam on evenly and it will receive an unusable product.

p0007When using shorter fibers are obtained, although a more uniform mixture, but the flexural strength of the product is reduced as compared to such with longer glass fibers.

p0008It has also been attempted to impregnate a bulky fiber mat with a foamable phenolic resin solution and then foam the phenolic resin solution. For this purpose, the fiber mat has been compressed, impregnated with the phenolic resin solution and the solution is then foamed under pressure, after it was sufficiently infiltrated into the mat. The method does not lead to satisfactory products, because the impregnated fiber mat obtained after compression is no longer its original thickness when the resin is foamed and so one obtains a relatively hard foam, the fiber reinforcement is often not properly embedded by the phenolic resin. In particular, a lightweight phenolic foam can not be obtained in this manner.

p0009The invention is based on the object to produce a particularly lightweight fiber-reinforced phenolic resin foam containing the reinforcing fibers distributed in a uniform shape.

p0010The reinforcing fibers have to be embedded completely and without defects in the phenolic foam. As the reinforcing fibers are provided in the essentially glass fibers.

p0011The inventive object is achieved by the reproduced in the claims process.

p0012The process is a development of the known method, -after which a nonwoven glass fabric is impregnated with a foamable phenolic resin solution and the phenolic resin is then foamed by supplying heat under embedding of the glass fibers, wherein the solvent evaporated.

p0013The object of the invention is achieved with such a method in that the reinforcing fibers are bonded with such a binder or binder mixture, which dissolves in the solvent for the phenolic resin or swells in its presence. A mat of glass fibers as reinforcing fibers, the optionally other reinforcing fibers such as textile synthetic fibers, asbestos fibers, ceramic fibers and / or carbon fibers are mixed is solidified with a binder or binder mixture of the type defined above. Suitable binders or binder mixtures can be determined by simple preliminary trials, in adapting to the choice of solvent for the phenolic resin. In general, binders based on polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, copolymers of itaconic acid and vinyl acetate or copolymers preferably selected from acrylic acid esters and acrylic acid.

p0014These binders are soluble or swellable in aqueous or alcoholic solutions. Such solutions are preferably in conjunction with phenolic resins of the resol type, from which can be produced very suitable foamable resin solutions.

p0015However, all binders or binder mixtures can be used which dissolve in the solvent for the phenolic resin or swell therein when the Phenölharzlösung is brought into contact with the glass fiber fleece.

p0016The fiberglass mat, which optionally said further reinforcing fibers are mixed, may be made on wet or dry roads. In general, a wet-laid nonwoven fabric is preferred, ie, a web which is made on the type of papermaking art.

p0017The glass or other reinforcing fibers to be provided according to at least 2 mm long and have a diameter of at least 3 microns. Preference is given to fibers having about 10 mm in length and a diameter of at least 9 microns. A wet-laid nonwoven fabric is preferred because it gives better mechanical properties be.i the hereby reinforced phenolic resin foam is generally due to the greater irregularity of the fiber deposition.

p0018The weight of the glass fiber nonwoven is at least 50 g / m² be. Preference is given to webs of at least 100 g / m²,

p0019The binder or binder mixture on the weight of the fibers added in amounts of 2 to 10 weight percent based. Preferred are amounts of 3 to 6 weight percent.

p0020The foamable phenolic resin solution is thereby obtained in that a phenolic resin is mixed with a conventional resol type curing and foaming agent. The proportions may be chosen adapted to the intended purpose. The foamable phenolic resin mixture in a suitable solvent, usually in aqueous or alcoholic base, is then brought together with the glass fiber fleece. It penetrates and impregnates the glass fiber fleece. If the so-impregnated and impregnated .nierte fiberglass mat is then heated, dissolves the binders or binder mixture of the fleece in the phenolic resin-solvent or it swells by the action. The foaming of the phenolic resin solution in solution-go with simultaneous or swelling of the binder spread the fibers very evenly in layers within the foaming resin. By the supply of heat-foaming and curing of the foam is simultaneously accelerated and to obtain a particularly lightweight foam containing the reinforcing fibers in unprecedented uniformity incorporated.

p0021In the inventive method, it is ensured that the phenolic resin solution permeates the nonwoven glass fiber fabric sides.

p0022In the production of thin layers of glass fiber reinforced lightweight phenolic resin foams, it is advantageous to conceal the one side glass fiber nonwoven mat with a suitable paper or a polyethylene film. This is to prevent the phenolic resin solution, which easily penetrates the glass fiber fleece, runs out at the back. When foaming is obtained also here very uniform fiber interspersed reinforced phenolic resin foams.

p0023The following examples illustrate the novel process.

example 1

p0024It is a nonwoven glass fiber fabric of 300 g / m² and a thickness of 0.5 mm prepared by dispersing 94 parts by weight of glass fibers with 10 microns in diameter and 13 mm length and 6 parts by weight fibrillated polyvinyl alcohol in water. From this suspension, a non-woven is deposited on the papermaking art, which is dried and solidified by exposure to heat.

p0025There is still a foamable phenolic resin solution by mixing 100 parts by weight of a phenolic resin with 80 percent by weight of solid components (trade name Plyophen TD 2520 Dainippon Ink & Chemicals, Inc.) And 10 parts by weight of a curing agent (trade name Catalyst F-20 of Dainippon Ink & Chemicals, Inc.) and 5 parts by weight of trichlorofluoromethane, and 5 parts by weight of tetrachlorodifluoroethane prepared.

p0026This mixture is applied to the above-mentioned glass fiber fleece in an amount of 1200 g / m², Based on the solid weight, applied. The web thus treated is heated to 140 ° C. The phenolic resin solution foams up and hardens.

p0027The phenolic resin foam obtained has a density of 0.05 g / cm '. The glass fibers are very uniformly distributed over the entire cross section of the shaped body in layers.

p0028The foam has an over conventional glass fiber-reinforced phenolic foam doubled bending stiffness.

example 2

p0029There is a phenolic resin foam of 30 mm thickness prepared with glass fiber reinforcement by a sheet of wrapping paper is connected on one side with a glass fiber fleece according to Example 1 by adhesive. The foamable phenolic resin solution from Example 1 is applied to the glass fiber fleece in an amount of 1200 g / m², Based on the solid weight was sprayed and that in the same manner as in the above example. The web thus treated is heated to 140 ° C, wherein the phenolic resin foams and hardens.

p0030The foamed resin has a density of 0.05 g / cm³ and contains glass fibers, which are distributed in a uniform layer. Near the wrapping paper, the fibers are spread slightly denser.

p0031The phenolic foam has an excellent flexural strength and wear resistance.

p0032All inventively prepared phenolic resin foam articles have good thermal insulation properties and are always very rigid. You have always uniform quality.