WO1992022603A1

WO1992022603A1 - Product of fibrous material and resin

Info

Publication number: WO1992022603A1
Application number: PCT/NL1992/000103
Authority: WO
Inventors: Adrianus Daniël SMOUT; Frans Kooimans
Original assignee: Dsm N.V.
Priority date: 1991-06-13
Filing date: 1992-06-11
Publication date: 1992-12-23
Also published as: BE1004947A4

Abstract

The invention relates to a semi-finished product consisting of firbrous material and a virtually powdered thermosetting resin having a glass transition temperature above 35 °C, a curing temperature at least 40 °C higher than the glass transition temperature, and a viscosity of less than 5000 Pas at a temperature between the glass transition temperature and the curing temperature, the resin particles being partly fused and partly in contact with the fibrous material.

Description

Product of fibrous material and resin

Field of the Invention The invention relates to a semi-finished product consisting of fibrous material and a powdered thermosetting resin.

Background of the Invention Semi-finished products and a process for their production are described in U.S. Patent No. 4,292,105. In the process an amount of powdered resin is dispersed in a liquid medium such as water and then applied to a fibrous material. The liquid medium is removed through evaporation and the powder particles adhere to the fibers by an adhesive.

The drawback of such a semi-finished product is that it can only be obtained via a laborious, lengthy and environmentally unsound process. Much energy is required to evaporate large amounts of water. A further drawback is the adhesive that is required, that may have an adverse effect on the properties of the end product.

A third drawback is that the semi-finished product has a rigid structure and is difficult to process in process steps such as compression molding.

The object of the present invention is to provide a semi-finished product that does not have the aforementioned drawbacks. Summary of the Invention The present invention relates to a semi-finished product that comprises a fibrous material and a virtually powdered thermosetting resin having a glass transition temperature of more than 35°C, a curing temperature at least 40°C higher than the glass transition temperature, and a viscosity of less than 5000 Pas at a temperature between the glass transition temperature and the curing temperature, the resin particles being partly fused and partly in contact with the fibrous material.

Such a semi-finished product is stable at room temperature and can be kept for a relatively long time. It contains an amount of fibrous material with an amount of powder adhered to it. The semi-finished product is a loose collection of powdered fibers.

The invention also relates to a process for the production of such a semi-finished product in which an amount of fibrous material is mixed with an amount of powdered thermosetting resin having a glass transition temperature of more than 35 °C, a curing temperature at least 40°C higher than the glass transition temperature, and a viscosity of less than 5000 Pas at a temperature between the glass transition temperature and the curing temperature, and which mixture is heated to a temperature above the glass transition temperature and below the curing temperature until the resin particles are at least partly fused and partly in contact with the fibrous material. After the fusion of the powder particles the semi¬ finished product obtained is allowed to cool so that the resin sets. It is of course possible to directly process the semi-finished product while it is still hot.

Detailed Description of the Invention

The mixing of the resin powder and the fibrous material can be effected in, for example, the following ways: by simply mixing the components by stirring; by mixing them in a drum; by using application methods employing a fluidized bed; by contacting the two components in a different manner with movement, by powdering a fibrous structure; or in a different manner.

The semi-finished product may be further processed to form a finished product or it may first be processed into a second semi-finished product. The semi-finished product comprising loose powdered fibers as described above will hereinafter be called the 'first semi-finished product'.

This first semi-finished product has good stability and is easy to handle. The fibers and the powder do not separate.

The second semi-finished product can be obtained by compression molding the first semi-finished product at a temperature below the curing temperature and is preferably obtained by compression molding at room temperature. During this compression molding the resin particles fuse further and mix with the fibers to form a reasonably coherent mass. The resin serves to connect the fibers.

The curing temperature is understood to be the temperature above which the resin composition thermosets. This curing temperature can be influenced by the type of accelerators, initiators and/or inhibiting agents used. Methods for the addition thereof and for the determination of the temperature are known to a person skilled in the art. The dimensions of the second semi-finished product are not subject to any limitations. The maximum and optimum sizes will be substantially dependent on the dimensions of the production and processing equipment. For most applications it will be advantageous if the second semi¬ finished product is a sheet. For example sheets of 100 cm x 100 cm or sheets of 1.22 m x 2.44 m. The thickness of the sheets may also vary. Preferably, they are between 1 and 50 mm thick, more preferably between 2 and 25 mm.

Like the resin in the first semi-finished product, the resin in the second semi-finished product has not yet set at all and the second semi-finished product can be hot- formed. This presents great freedom in further processing steps. Because the second semi-finished product is a coherent whole mass, no, or virtually no, fibrous material or thermosetting powder is lost. Because of this same coherence the semi-finished product is also easy to handle and can easily be stored and transported.

The second semi-finished product can be entirely or almost entirely solid. This can be influenced via the choice of the ratio of the resin and the fibrous material. If the material is then firmly compression molded the second semi¬ finished product will contain no or virtually no cavities. If the resin and the fibrous material are lightly scattered on top of one another and are not compression molded too firmly, a second semi-finished product will be obtained that contains many cavities. A method can be chosen depending on the application.

The second semi-finished product can be adjusted to the dimensions of the molded part that is to be made from it by, for example, breaking or sawing or by combining several pieces of semi-finished product.

The first and the second semi-finished product can be processed into molded parts in all possible ways, for example by curing at elevated temperature, optionally under pressure. The first semi-finished product can be very well processed with the aid of an extruder. It is also possible to heat the second semi-finished product to above the glass transition point and to then mold it and subsequently cure it at an elevated temperature and, optionally, pressure. Another possibility is to grind or chop the second semi¬ finished product into smaller parts and to process those parts by elevating the temperature and, optionally, the pressure. This could optionally be done with the aid of an extruder. With an extruder it is possible to produce for example (profiled) bars. This is of course also possible with the first semi-finished product.

Because the second semi-finished product can be hot-formed, it is possible to use the second semi-finished product to manufacture a third semi-finished product that already has the shape and the dimensions of the molded part to be produced, also without the resin of this third semi- finished product setting. This third semi-finished product can then be processed into the molded part later, depending on the circumstances and requirements.

It is also possible to process the resin and fibrous material into a molded part directly in the first step, by not only melting the resin powder but also heating it to such a temperature as to effect curing of the resin. A molded part is understood to be a molded, cured semi-finished product. Because the resin is cured the molded ' part retains its shape over a wide temperature range. The resin composition is preferably solid at room temperature. Suitable resins are for example the styrene- free unsaturated polyesters, crystalline polyesters, di(iso)allylphthalate resins, bismaleimides, diallylisocyanurate resins, epoxy resins and combinations thereof. Preferably, the resin is chosen from the unsaturated polyesters, the bismaleimides or from the epoxies that are solid at room temperature.

Particularly suitable are unsaturated polyesters. For high temperature application epoxies and bismaleimides are very usefull.

These unsaturated polyesters are generally composed of one or more aliphatic, cycloaliphatic, and/or aromatic mono-, bi- and/or polyvalent alcohols and one or more aliphatic, cycloaliphatic and/or aromatic mono-, bi- or polyvalent carboxylic acids and, if so desired, esters derived therefrom.

The carboxylic acids are at least partly unsaturated. The polyester may also be partly composed of saturated dicarboxylic acids. Examples of suitable alcohols are benzyl alcohol, ethylene glycol, propylene glycol, neopentyl glycol, hexane diol, cyclohexane dimethanol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol and/or dipentaerythritol. Instead of, or in addition to, the alcohol compound(s) one or more epoxy compounds may be used such as ethylene oxide, propylene oxide and/or allylglycidyl ether. Examples of suitable bi- or polyvalent carboxylic acids are maleic acid, fumaric acid, itaconic acid, citraconic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, tetrahydrophthalic acid, hexahydrophthalic acid, hexachloroendomethylene tetrahydrophthalic acid, dichlorophthalic acid, isophthalic acid, terephthalic acid and/or trimellitic acid. The carboxylic acid can also be used in the form of an anhydride, for example maleic anhydride or pht alic anhydride. Preferably, maleic anhydride is used in combination with isophthalic acid and/or orthophthalic acid.

If so desired, the unsaturated polyester may also contain saturated or unsaturated monocarboxylic acids such as synthetic and/or natural fatty acids with between 2 and 36 carbon atoms or esters prepared from these carboxylic acids and polyvalent alcohols such as glycerol. Examples of suitable monocarboxylic acids are lauric acid, stearic acid, oleic acid, linoleic acid, benzoic acid, acrylic acid and/or methacrylic acid. The resin composition preferably sets at a temperature between 80 and 200°C. More preferably, the resin composition sets at a temperature between 90 and 150°C, most preferably at a temperature between 100 and 150°C. The molded part is preferably obtained via compression molding at a pressure between 1 kg/cm² and 200 kg/cm² , more preferably a pressure between 5 and 15 kg/cm². Powders of the resin composition according to the invention can be obtained in all possible ways, for example by grinding a cooled resin composition. The resin composition generally also contains initiators. The initiators used are dependent on the resin used and on .the desired curing temperature. Suitable initiators are peresters, peralcohols, peracids, percarbonates, perethers, diacylperoxides, dialkylperoxides, azo compounds, C-C labile compounds and ketone peroxides. Examples are tert. butyl peroxide, lauroyl peroxide, benzoyl peroxide, ditert. butyl peroxides, dibenzoyl peroxide, dicumyl peroxide, tert. butyl perbenzoate, tert. butyl peroctoate, tert. butyl perpivalate, cobalt octoate, bis-4- tert. butyl cyclohexylperoxydicarbonate, azodiisobutyro- nitrile and tetra-substituted dibenzyl compounds. In addition, accelerators may be present, for example cobalt salts and n,n-dimethylaniline.

In addition, the usual additives may be added to the resin composition, for example fillers, flame retardants, pigments, stabilizers, etc. It is also possible to add mold-release agents to the resin composition. This presents the advantage that such mold-release agents need no longer be added in a later processing step or need not be applied to" the mold. The resin composition preferably comprises 10-99.9 wt.% resin, 0-80 wt.% fillers, 0.1-5 wt.% initiator system and 0-20 wt.% monomers that are reactive with the resin, the weight percentages being percentages relative to the overall resin composition.

If the resin is an unsaturated polyester, the aforementioned monomers are preferably also unsaturated. The monomers are preferably not volatile below 70°C and, more preferably, they are not volatile at all under the processing conditions. As the monomer, use may be made of for example compounds such as triallylcyanurate, triallylisocyanurate, trimethylolpropane triacrylate and diallylphthalate.

The aforementioned components are preferably mixed in the melt, for example in an extruder, a mixer or a kneader, the initiator being added last, directly before cooling.

The first or second semi-finished product preferably comprises 5-50 wt.% resin composition, relative to the semi-finished product, and 95-50 wt.% fibrous material. The fibrous material may consist of all kinds of fibers in all possible embodiments. They may be thick or thin, long or short fibers. The fibers may be used in structures, for example non-woven mats, mats, fabrics, or knits, or as loose fibers, for example so-called chopped rovings. They may be bundled or single filaments.

The material of the fibers may be any material available in the form of fibers, for example glass fibers, carbon fibers, plastic fibers such as polyethylene or aramide fibers or other thermoplastic or thermosetting fibers, metal fibers, ceramic fibers, textile fibers or vegetable fibers such as wood, jute, sisal or coconut fibers. Preferably the material consists of glass or vegetable fibers.

It is also possible to use combinations of different types of fibers or fiber embodiments.

If wood fiber is chosen as the fibrous material a molded part can be obtained that resembles the well-known chipboard. Such a molded part according to the invention presents the advantage that no chipboard gas (formaldehyde) can be released.

The fibrous material may also be entirely or partially replaced by sawdust.

It is also advantageous to incorporate amounts of recycled material into the semi-finished product, such as chips, flakes or dust of grounded parts. Those parts can consist of thermoplastic or thermoset material, and it can be with fibrous reinforcements or without. Examples are grounded molded parts such as molded SMC (Sheet Molding Compound) or BMC (Bulk Molding Compound) . Especially for automotive parts made from fiber reinforced thermoset materials this is a very good way of recycling. The recycled material can replace the fibrous material entirely or partially. The possible ratio's depend mainly of the required strength of the resulting product. A usefull ratio is for example 10-70 parts by weight of recycled material to 90-30 parts by weight of (glass or wood) fibers. One or more sides of the second semi-finished product can be provided with a coating that has a different composition than the second semi-finished product. This may be a coating of the resin composition without the fibrous material or with a lower percentage of fibrous material or with a different type of fibrous material. The coating can be applied in all kinds of ways, for example by spraying, rolling, brushing, casting or injecting. This coating can also be a sheet, a non-woven mat or a film that is applied. In addition, one or more sides of the molded part can be provided with a coating that has a different composition than the first or the second semi-finished product. This can be done in the same manner as described above. It can also be done with a powder-in-mold-coating method as described in EP-B-0.001.865 or a liquid-in-mold- coating method (LIMC). LIMC is a method whereby a compression molding compound, for example the first or the second semi-finished product according to the invention, is compression-molded in a mold and is at least partly cured, after which the mold is opened slightly, for example a few mm, and whereby an amount of coating material is injected between the mold and the compression-molded part. The whole is then cured.

The first or the second semi-finished product or the molded part can then be processed with other structures to form sandwich products. If for example two sheet-shaped semi-finished products or molded parts are combined with an additional layer between the two, it is possible to take advantage of the strength of both of the semi-finished products or molded part layers while keeping the weight low if the additional layer has a lower specific gravity than the molded parts. A variant of this is a sandwich consisting of several layers of the first or second semi-finished product or molded part, whereby certain layers have a greater specific gravity than others.

It is possible to combine a Sheet Molding Compound (SMC) or Bulk Molding Compound (BMC) with a first or second semi-finished product or molded part according to the invention. This can be done, for example, to manufacture a sandwich structure as described above.

The invention will be illustrated with the aid of the following examples, without being limited thereto.

Example I

The first semi-finished product

85 g of wood fibers with a length of between 0.1 and 20 mm was heated at 80°C for 30 minutes. Then, 15 g of powdered resin with the following composition was distributed over the wood fibers with the aid of a screen with 104-μm openings.

Composition:

45.2% Synolite 9193 HV from DSM Resins as an unsaturated polyester resin without monomer,

47.2% calcium carbonate as a filler, 3.4% zinc stearate as a mold release agent,* 1.7% cobalt octoate and tert. butyl perbeήzoate as an initiator system, 2.5% triallylcyanurate as a high-boiling copolymerisable monomer.

The fibers and the powdered resin were homogenised in a mixer heated to 80°C. The powdered resin attached itself to the surface of the fibers.

Example II

The second semi-finished product

An amount of the first semi-finished product of Example I was introduced into the cavity of a Philips flow mold with a diameter of 9 cm.

The press was closed for 60 seconds at a pressure of 70 kg/cm². The temperature was 80°C.

The thickness of the sheets obtained (the second semi-finished product) was varied by varying the amount of first semi-finished product. The sheets were 5 and 10 mm thick. The resin was not cured under these compression molding conditions.

Example III

An amount of the first semi-finished product of Example I, which was still hot, was introduced into a Philips flow mold of 150°C. The press was closed for 240 seconds, at a pressure of 70 kg/cm², which caused the resin to cure. The sheets were between 4 and 10 mm thick, dependent on the amount of first semi-finished product. The ^• sheets had smooth surfaces. The strength of the sheets was better than that of a conventional chipboard of the same thickness.

Example IV

The procedure of Example I was followed, except that 85 g of wood powder (sawdust) was used instead of wood fiber. The dimensions of the powder were between 1 and 500 μm.

Example V The procedure of Example II was followed, using the mixture of Example IV. Each of the sheets constituted a coherent whole mass.

Example VI The mixture of Example IV was processed as described in Example III. The sheets had smooth surfaces. The edges were smooth and showed no pores. The strength was slightly lower than that of the sheets of Example III but was still comparable with that of a conventional chipboard. The experiment was repeated using 25 g of powdered resin and 75 g of wood fibers instead of 15 g of powdered resin and 85 g of wood fibers. The strength of the sheets thus obtained (of the same thickness) was better than that of the sheets of Example III. The sheets looked like "hard board." Example VII

The sheet of Example II or Example V was placed in a press at 150°C. A layer of SMC, consisting of a glass fiber-filled unsaturated polyester, was applied to the sheet. The press was closed and its contents were compressed for 240 s, using 70 kg/cm². The bond between the wood/powdered resin molded part and the SMC of the resultant sheet was good.

Comparative Experiment A

The procedure of Example I was repeated at room temperature. The result was an amount of material consisting of a bottom layer of in particular powdered resin and a top layer of in particular wood fibers.

Claims

C L A I M S

1. Semi-finished product comprising fibrous material and a virtually powdered thermosetting resin having a glass transition temperature of more than 35°C, a curing temperature at least 40°C higher than the glass transition temperature, and a viscosity of less than 5000 Pas at a temperature between the glass transition temperature and the curing temperature, the resin particles being partly fused and partly in contact with the fibrous material.

2. The semi-finished product of claim 1, wherein the resin composition sets at a temperature between 80 and 200°C.

3. The semi-finished product of claim 1 or 2, wherein the resin composition comprises:

10-99.9 wt.% resin; 0-80 wt.% fillers; 0.1-5 wt.% initiator system; and

0-20 wt.% monomers that are reactive with the resin, the weight percentages being percentages relative to the overall resin composition.

4. The semi-finished product according to any one of claims 1-3, wherein the resin is an unsaturated polyester which comprises one or more aliphatic and/or cycloaliphatic mono- bi- and/or polyvalent alcohols and one or more aliphatic, cycloaliphatic and/or aromatic bi- or polyvalent carboxylic acids and, optionally, mono- carboxylic acids and/or esters derived therefrom.

5. The semi-finished product according to any one of claims 1-4, wherein the semi-finished product comprises 5-50 wt.% resin composition, relative to the semi-finished product, and 95-50 wt.% fibrous material.

6. The semi-finished product according to any one of claims

1-5, characterised in that the fibrous material consists of vegetable fibers.

7. The semi-finished product according to any one of claims

1-5, characterised in that the fibrous material consists of glass.

8. The semi-finished product according to any one of claims 1-7, characterised in that the product comprises ground recycled material.

9. A process for the, production of a semi-finished product comprising mixing an amount of fibrous material with an amount of powdered thermosetting resin having a glass transition temperature of more than 35°C, a curing temperature at least 40°C higher than the glass transition temperature, and a viscosity of less than 5000 Pas at a temperature between the glass transition temperature and the curing temperature, and heating the admixture to a temperature above the glass transition point and below the curing temperature until the resin particles are at least partly fused and at least partly in contact with the fibrous material.

10. A second semi-finished product, consisting of a fibrous material and a virtually powdered thermosetting resin having a processing temperature above 35°C, a curing temperature at least 40°C higher than the processing temperature, and a viscosity of less than 5000 Pas at a temperature between the processing temperature and the curing temperature, the resin particles being fused and mixed with the fibrous material to such an extent that the semi-finished product constitutes a coherent whole.

11. The second semi-finished product of claim 10, wherein at least one side of the semi-finished product is provided with a coating with a different composition than the semi-finished product.

12. The second semi-finished product claim of 10, wherein the second semi-finished product has the form of a sheet and is between 1 and 50 mm thick.

13. A molded part obtained by processing and at the same time curing at least one semi-finished product according to any one of claims 1-8 or according to any one of claims 10-12.

14. The molded part of claim 13, wherein at least one side of the molded part is provided with a coating of a different composition than the molded part.