WO1999050341A1 - Low-pressure sheet moulding compound - Google Patents

Abstract

The invention relates to a low-pressure sheet moulding compound (SMC) for producing fibre-reinforced components, a method for producing such a low-pressure SMC, the use of said low-pressure SMC for the production of fibre-reinforced components and components made from the low-pressure SMC.

Description

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Low pressure SMC for the production of fiber reinforced components

The invention relates to low-pressure SMC for the production of fiber-reinforced components, methods for producing this low-pressure SMC, the use of this low-pressure SMC for the production of fiber-reinforced components and the components produced from this low-pressure SMC.

SMC stands for "Sheet Molding Compound" and is the English name for a resin mat according to DIN 16913. SMC is generally used to refer to a flowable resin mat with isotropic properties and random fiber distribution in the mat plane. SMC is a flat resin mat based on unsaturated polyester resin or vinyl ester resin Glass fibers are usually used as reinforcement fibers, but other materials are also suitable for reinforcement: A typical SMC recipe consists of approx. 30% polymer, approx. 30% filler and approx. 30% glass fibers, the rest consists of additives together, such as color pigments, hardeners, dispersing aids and similar substances. SMC is produced from a resin master paste and reinforcing fibers. The resin master paste is applied to two carrier foils. These carrier foils are drawn by the SMC machine and thereby transport the resin paste onto which the reinforcing fibers giant lt or be hung up. After the reinforcing fibers have been applied, both foils are pressed together so that a kind of sandwich is created. This sandwich is pulled through an impregnation line, which uses pressure and flexing movements to ensure that the fibers are evenly wetted with the resin. At the end of the machine, it is wound on rolls. A ripening process that can be initiated in a chemical and / or physical manner is of crucial importance. After this maturation process, the SMC can be processed further.

After the carrier foils have been removed, the SMC is usually processed into molded parts in heated steel tools. The mold temperature is generally about 135 to 155 ° C.

CONFIRMATION SKILLS - 2 -

The decomposition of the hardener is started by the mold temperature and the molding compound undergoes an exothermic crosslinking reaction. When processing in press tools, the material is usually dosed manually. Maintaining precise dosing quantities is generally very important for problem-free production. For this, the SMC is not only cut according to templates, but also weighed. Weighing out the blank serves as a control and enables a possible correction of the blank. Then the SMC is placed on the tool and the tool is closed. The pressure is applied and held until the molded part is completely hardened.

In the case of the standard SMC used up to now, in addition to the starting temperature of approx. 135 to 155 ° C, a relatively high pressure of at least 50 to 100 bar is required. These pressures are necessary to distribute the standard SMC, which is flowable at high temperatures, evenly in the mold. However, these high pressures cannot be used to manufacture some components.

The object of the present invention was therefore to provide SMC mats which can be used even at pressures <10 bar, preferably from 1 to 2 bar and at temperatures <70 ° C.

According to the invention, this object was achieved by an SMC with the characteristics of the main claim. Refinements are preferably characterized in the subclaims.

The low-pressure SMC according to the invention could surprisingly be achieved by developing a special SMC recipe.

The resin mixture must be able to completely compound the reinforcing fibers and to further process the SMC thus obtained to build and - 3 -

To enable molded parts at the lowest possible temperatures and low pressures.

The SMC according to the invention contains as a base paste a mixture of at least one unsaturated polyester resin or vinyl ester resin as the base component, at least one shrinkage-compensating additive, at least one hardener and additives. As the unsaturated polyester resin, the base paste preferably contains at least one resin based on maleic acid, isophthalic acid or orthophthalic acid. Saturated polyesters, for example based on polyurethane, polyvinyl acetate, polymethyl methacrylate, polystyrene or styrene-butadiene, or mixtures of these additives, are added to this base component as a shrinkage-compensating additive. Suitable components are known per se to the person skilled in the art and are commercially available for semi-finished SMC products.

Organic peroxides that start at the lowest possible temperatures are used as hardeners. Examples include t-butyl per-2-ethylhexanoate, bis- (4-t-butylcyclohexyl) peroxydicarbonate, benzoyl peroxide and methyl isobutyl ketone peroxide. Mixtures of these peroxides, which are known per se in SMC technology, can also be used.

As further components, this resin base paste also contains the usual additives known to those skilled in the art, such as additives to ensure storage stability, additives for deaeration, thixotropic agents, thickening aids, fillers and pigments, and, depending on the application, adhesives and / or release agents. These additives include, for example, the known components which stabilize peroxide-containing UP resin batches, the known foam-inhibiting polymers, silicas such as, for example, aerosils, calcium carbonate, aluminum trihydrate, kaolin and barium sulfate. - 4 -

The stock paste according to the invention contains 10 to 34% by weight, preferably 17 to 34% by weight, of unsaturated polyester resin, 1 to 15% by weight, preferably 1.5 to 13.5% by weight of shrinkage-compensating additive, and at least one hardener in amounts which preclude undercuring, preferably 0.1 to 2% by weight hardener. Up to 0.2 wt.%, Preferably 0.03 to 0.15 wt.% Inhibitor, up to 0.2 wt.%, Preferably 0.03 to 0.15 wt.% Deaerator can be used as additives , up to 2 wt.%, preferably 0.15 to 1 wt.% thixotropic agent, up to 0.2 wt.%, preferably 0.15 to 0.1 wt.% thickening aid, 1 to 30 wt. %, preferably 4 to 24% by weight of fillers and up to 4% by weight, preferably 0.15 to 2% by weight of pigment, and, depending on the application, 1 to 15% by weight, preferably 1.5 to 13.5% by weight of adhesive and / or 1 to 2% by weight, preferably 1.2 to 1.8% by weight of release agent can be added.

These components are dispersed intensively in appropriate dissolvers. The necessary thickening can be initiated both chemically and physically. In the case of chemical thickening, the resin paste is mixed with a thickener and applied to two carrier foils. Alkali and / or alkaline earth metal oxides or hydroxides and / or isocyanates can be used as thickeners. Magnesium oxide paste for thickening SMC, magnesium hydroxide and / or calcium hydroxide may be mentioned by way of example. 0.1 to 2% by weight, preferably 0.15 to 1.7% by weight, of thickening agent can be added to the stock paste. The carrier foils charged with the resin paste according to the invention are then drawn through the SMC machine as usual and sprinkled or coated with the reinforcing fibers. Depending on the required strength, 10 to 70% by weight, preferably 20 to 60% by weight, of reinforcing fibers are embedded. The reinforcing fibers can be used as a mat, fabric, fleece or as clippings or as combinations of these shapes. Other possible reinforcing fibers are: carbon fibers, kevlar, aramid, polymer fibers or fibers made from renewable raw materials such as flax, hemp, banana or coconut. Combinations of these materials can also be used. - 5 -

The rest of the process is the same as for standard SMC. After the ripening process (chemical and / or physical thickening), the low-pressure SMC according to the invention thus produced can be processed further.

With the aid of the resin mixture according to the invention, it was thus possible for the first time to provide a low-pressure SMC which can be processed at low temperatures and even at a pressure of 1 to 2 bar.

The low-pressure SMC according to the invention can be used in a variety of ways. In particular, it can be used for the production of fiber-reinforced components, which should offer good temperature and media resistance as well as high rigidity, strength and impact strength even at low temperatures. The low pressure SMC is therefore particularly suitable for automotive parts and applications that are open to the public. Due to its good mechanical properties, the low-pressure SMC is also the ideal material for the electrical, furniture and sanitary industries. Because of its property of being processable even at low pressures and temperatures, the low-pressure SMC according to the invention is particularly suitable for producing sandwich elements.

This is to be demonstrated using the example of a component from the commercial vehicle sector.

The state of the art for commercial vehicles is box bodies made of sheet steel, made of a steel-wood composite construction, and for temperature-controlled containers in particular bodies made of sandwich elements. Such sandwich elements have a cover layer and a core on the outside and inside. The cover layers can consist of metal or plastic materials.

The sandwich elements used for temperature-controlled containers should preferably have a high degree of rigidity with a low weight. In particular in the floor area of the load from forklifts, in the side - 6 -

wall area can withstand the load from storey loading and in the roof area from the load by hanging loads. In order to be able to be used when transporting frozen products, for example, they have to ensure that the low transport temperature is maintained at high outside temperatures.

In addition to the sandwich elements with metal cover layers, plastic sandwich elements with a length of up to approximately 16,000 mm in various widths and thicknesses are known. The core of each of these elements is enclosed on all sides by plastic cover layers. There are no metallic thermal bridges in these elements. These sandwich elements are self-supporting and achieve a high payload for the entire vehicle due to their low weight. Depending on the dimensions of the container, they are manufactured in customized shapes.

So far, these sandwich elements have been manufactured using the so-called Naßin-Naß process. Isoier plates with glass fiber mats, which must be soaked with liquid resin, are enclosed on all sides.

Such sandwich elements can be produced with the help of the low-pressure SMC according to the invention, for example in the following way: The shape required for the elements is cleaned as usual and adjusted to the required dimensions. The mold and the mold cover are provided with a release agent in order to be able to remove the finished element from the mold without problems. A gel coat (fine-layer resin) with a self-separating effect is preferably used. It consists, for example, of unsaturated, thixotropic polyester resin based on dicarboxylic acid neopentyl glycol in a highly reactive setting and is characterized by high water resistance and mechanical resistance. Alternatively, the gel coat can also be integrated in the low-pressure SMC according to the invention. - 7 -

Instead of the gel coat, a single-layer or multilayer film or lacquer film can also be inserted into the mold or into the mold cover. The insertion of the film can expediently be facilitated by suction using a vacuum. If a multilayer film is used, it expediently consists of a carrier film with an applied layer of colored lacquer and clear lacquer. Several layers of lacquer can also be applied. The sandwich element can be individually designed using such a single-layer or multilayer or lacquer film. In this way, painting, so to speak, can be integrated into the manufacturing process of the sandwich elements according to the invention.

After a surface fleece, for example made of glass fibers or polyester fibers and impregnated with UP resin, is inserted into the mold as described above to compensate for the structure, the first layer of the low-pressure SMC webs is inserted. The foam sheets tailored to the vehicle, including any necessary reinforcements made of wood, metal or reinforcements made of low-pressure SMC sheets, are inserted into the mold. Then another low-pressure SMC web and the cover fleece is placed on top and the mold is coated with a release agent, gel coat or with a multi-layer or. Lacquered lid closed. The foam sheets, which serve as spacers and insulation, should have a low density, high pressure resistance, low thermal conductivity and should also be environmentally friendly. Polyurethane plates or plates made of thermoplastic material, for example polystyrene, are advantageously used as the foam plate.

In principle, a multi-layer low-pressure SMC structure of the sandwich elements is of course also possible, for example by providing not only cover layers and reinforcements made of low-pressure SMC, but also intermediate layers or other structures made of low-pressure SMC. - 8th -

The closed mold is inserted into the hot plate press and at a temperature which depends on the hardener used and is sufficient for the hardener to start, preferably at about 60 ° C., a pressure which is sufficient for the intimate connection of the foam plates with the low-pressure SMC , preferably pressed at a pressure of 1 to 2 bar.

Overall, the process for producing the sandwich elements according to the invention reduces the emission of hydrocarbons by using the low-pressure SMC. With the use of the low pressure SMC it is possible for the first time to obtain a significantly improved surface structure. Furthermore, the amount of waste liquid resin is significantly reduced. The new process offers a high level of automation compared to the state of the art.

Figure 1 shows the schematic structure of a sandwich element according to the invention. The numbers mean: (1) gel coat; (2) surface fleece, (3) hardened low pressure SMC, (4) foam sheet.

Claims

- 9 patent claims 1. Sheet Molding Compound (SMC), characterized in that it contains a mixture of at least one unsaturated polyester resin or vinyl ester resin, at least one shrinkage-compensating additive, at least one hardener, additives and reinforcing fibers. 2. Sheet Molding Compound (SMC) according to claim 1, characterized in that it contains as unsaturated polyester resin at least one resin based on maleic acid, isophthalic acid, orthophthalic acid or mixtures of these resins and at least one shrinkage compensating additive selected from the group of saturated polyesters , preferably from a saturated polyester based on polyurethane, from polyvinyl acetate, polymethyl methacrylate, polystyrene, styrene-butadiene or mixtures of these additives. 3. Sheet molding compound (SMC) according to claim 1 or 2, characterized in that it contains as the hardener organic peroxides which start at the lowest possible temperatures, preferably t-butyl-per-2-ethyl-hexanoate, bis- (4- Contains t-butylcyclohexyl) peroxydicarbonate, benzoyl peroxide and methyl isobutyl ketone peroxide or mixtures of these peroxides. 4. Sheet Molding Compound (SMC) according to one or more of claims 1 to 3, characterized in that it contains additives to ensure storage stability, additives for ventilation, thixotropic agents, thickening aids, fillers and pigments as additives as well as, depending on Application contains adhesives and / or release agents. 5. Sheet Molding Compound (SMC) according to one or more of claims 1 to 4, characterized in that it is 10 to 34 wt .-%, preferably 17 to 34 wt .-% unsaturated polyester resin, 1 to 15 wt .-%, preferably 1.5 to 13.5% by weight of shrinkage-compensating additive, - 10 - and at least one hardener in amounts which preclude undercuring, preferably 0.1 to 2% by weight hardener, as additives up to 0.2% by weight, preferably 0.03 to 0.15% by weight inhibitor, up to 0.2 wt.%, preferably 0.03 to 0.15 wt.% deaerator, up to 2 wt.%, preferably 0.15 to 1 wt.% thixotropic agent, up to 0.2 wt %, preferably 0.15 to 0.1% by weight of thickening aids, 1 to 30% by weight, preferably 4 to 24% by weight of fillers and up to 4% by weight, preferably 0.15 to 2 % By weight of pigment substances and, depending on the application, up to 15% by weight, preferably 1 to 13.5% by weight of adhesive and / or up to 2% by weight, preferably 1 to 1.8% by weight Release agent and 10 to 70 wt .-%, preferably 20 to 60 wt .-% reinforcing fibers. 6. Sheet molding compound (SMC) according to one or more of claims 1 to 5, characterized in that it additionally contains thickeners, preferably alkali and / or alkaline earth oxides or hydroxides and / or isocyanates, particularly preferably magnesium oxide paste for thickening Contains SMC, magnesium hydroxide and / or calcium hydroxide. 7. Sheet molding compound (SMC) according to one or more of claims 1 to 6, characterized in that it contains 0.1 to 2 wt .-%, preferably 0.15 to 1.7 wt .-% thickener. 8. Sheet molding compound (SMC) according to one or more of claims 1 to 7, characterized in that it contains as reinforcing fibers glass fibers, carbon fibers, Kevlar, aramid, polymer fibers, fibers from renewable raw materials or combinations of these reinforcing fibers. 9. resin paste for the production of sheet molding compound (SMC) according to any one of claims 1 to 6, characterized in that it 10 to 34 wt .-%, preferably 17 to 34 wt .-% unsaturated polyester resin, 1 to 15 wt .-% %, preferably 1.5 to 13.5% by weight of shrinkage compensation - 1 1 - additive, and at least one hardener in amounts which exclude undercuring, preferably 0.1 to 2% by weight hardener, as additives up to 0.2% by weight, preferably 0.03 to 0.15% by weight. % Inhibitor, up to 0.2% by weight, preferably 0.03 to 0.15% by weight of deaerator, up to 2% by weight, preferably 0.15 to 1% by weight of thixotropic agent, up to 0 , 2% by weight, preferably 0.15 to 0.1% by weight of thickening aid, 1 to 30% by weight, preferably 4 to 24% by weight of fillers and up to 4% by weight, preferably 0, 15 to 2% by weight of pigment substances and, depending on the application, up to 15% by weight, preferably 1 to 13.5% by weight of adhesive and / or up to 2% by weight, preferably 1 to 1.8% by weight % Separating agent and optionally 0.1 to 2% by weight, preferably 0.15 to 1.7% by weight of thickening agent, the components being defined according to one of Claims 1 to 6. 10. A process for the production of sheet molding compound (SMC) according to one of claims 1 to 8, characterized in that the resin according to claim 9 is applied to two carrier films, drawn through an SMC machine and with 10 to 70% by weight. %, preferably 20 to 60% by weight of reinforcing fibers is sprinkled or coated. 1 1. Use of a sheet molding compound (SMC) according to one of claims 1 to 8 for the production of components with fiber-reinforced layers. 12. Use of a sheet molding compound (SMC) according to one of claims 1 to 8 for the production of components with fiber-reinforced layers for the automotive, electrical, furniture, sanitary and telecommunications industries. 13. Component with fiber-reinforced layers, characterized in that the fiber-reinforced layers are produced from a sheet molding compound (SMC) according to one of claims 1 to 8. - 12 - 14. Sandwich element made of plastic cover layers and a core, characterized in that the plastic cover layers are produced essentially from a sheet molding compound (SMC) according to one of claims 1 to 8.