CZ2013220A3 - Pressure membrane for vacuum molding of polymer composite parts - Google Patents

Abstract

The pressure diaphragm for the vacuum molding of polymer composite parts consists of a 0.5 to 2 mm sheet material of a diene elastomer rubber compound or a mixture of diene elastomers with a crosslinking degree of 40 to 85% crosslinks, ductility of 200 to 800%, hardness 20 to 70 ShA and temperature resistance up to 130 to 180 degC. Preferably, the material is gas impermeable, wherein the diene elastomer is at least one rubber selected from the group consisting of butyl rubber or halobutyl rubber, chloroprene rubber and EPDM copolymer.

Description

Pressure diaphragm for vacuum molding of polymer composite parts

Technical field

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure diaphragm for vacuum molding of polymer composite panels to overlap and press the process layer of a molded polymer composite deposited on a mold part of a mold. In particular, these are thermosetting matrix composites comprising dispersed particles of at least one filler and / or an at least one layer of reinforcing material.

BACKGROUND OF THE INVENTION

In vacuum molding with flexible sheets, two basic methods of vacuuming are used. The first is surface vacuum, in which the technological materials are laid on one side of the mold, and then vacuum pressing takes place on that one side of the mold. In this case, the foil is fixed to the mold, for example, by means of a double-sided sealing tape. However, this method is time-consuming and requires skilled personnel to handle relatively complicated film fastening. In addition, the foil and the sealing tape are sent to waste after the cycle has ended.

To some extent, these drawbacks are eliminated by the newly designed mold assembly for vacuum molding of polymer composite parts. The mold assembly is formed by a bottom frame on or in which a mold with a positive or negative shaped part corresponding to the shape of the article is placed. At least one technological layer of the molded polymer composite is deposited on this mold part of the mold and the mold with this layer, respectively. The layers of the molded polymer composite are covered with a pressure foil or membrane. It is then fixed with its edges to the edge portions of the mold and / or the lower frame by means of the enclosed upper clamping frame and at least two clamps.

Even in this case, however, disposable films made mostly of PA (nylon), PE, PI or even PTFE (especially for high curing temperatures) are mostly used. The material is chosen according to the type of matrix, the temperature of use and the complexity of the product. When selecting these films, it is necessary to take into account, in particular, chemical resistance and compatibility with vacuum materials and matrices, and the technology-specified temperature regime. The film thicknesses range from 25 to 50 µm. Efforts to increase the durability of the press-on foils used have led to the use of silicone elastomer-based membranes, known, for example, from the use of vacuum presses according to U.S. Pat. 4078962 or PCT International Application WO 02094546. Although silicone elastomer membranes are useful in multiple press cycles, they are not always physical

• 1 properties optimum in terms of the vacuum molding process of thermosetting matrix composites comprising dispersed filler particles and / or an intermediate layer of reinforcing material.

U.S. Pat. No. 2006289119 discloses a molding device having a long-life membrane based on a vulcanized diene elastomer - in particular, butyl rubber is disclosed. Similarly, in the European patent application 2541621, a laminator is provided which is provided with an olefin rubber (EPDM) membrane with a Shore A hardness of 35 to 80 and a thickness of 2 to 6 mm. Both solutions are a combination of a technique known as membrane vacuum forming and hydroforming. They have the fundamental disadvantage that, when shaping the material to be processed into a product, the materials and blanks are stressed and deformed by disadvantageous combined forces. From the fundamentals of physics and especially the mechanics, the decomposition of forces during material bending, material stretching and its combined stress are known. Since the above-mentioned cases involve the shaping of polymers in an unfinished physical state, especially in the case of tensile deformation and extreme combined stress, the materials of the workpiece are improperly deformed at the predominant forces and reduce the quality of the product in terms of uniform wall thickness.

The solution according to the invention differs in that the membrane material used (a diene elastomer based rubber compound or a diene elastomer mixture having a degree of crosslinking of 40 to 85% of the crosslinks) is in a state where it is partially elastic and partially plasticized. This allows it to be easily transformed into a 'form mold' and at the same time into a diaphragm, which better exerts forces on extremely stressed edges and dimensionally smaller form parts. During use, the membrane is gradually vulcanized (the degree of crosslinking of the rubber mixture gradually increases with repeating vacuum pressing cycles).

SUMMARY OF THE INVENTION

The pressure diaphragm for vacuum pressing of the polymer composite parts according to the invention contributes to the above-mentioned drawbacks to a large extent. The membrane consists of a sheet of 0.5 to 2 mm thickness of a diene elastomer-based rubber compound or a mixture of diene elastomers with a degree of crosslinking of 40 to 85% of crosslinks, an elongation of 200 to 800%, a hardness of 20 up to 70 ShA and temperature resistance up to 130 to 180 ° C.

Preferably, the rubber sheet has a degree of cross-linking of 80 to 90% cross-links, an elongation of 500 to 600%, a hardness of 50 to 60 ShA, and a temperature resistance of up to 130 to 180 ° C. Preferably, it is a gas impermeable material, wherein the diene elastomer is

at least one rubber selected from the group consisting of butyl or halobutyl rubber, chloroprene rubber and EPDM copolymer. Preferably, during use of the membrane, the degree of crosslinking of the rubber composition gradually increases with repeating vacuum pressing cycles.

Examples νγ nai * iuExample 1

The pressure diaphragm for vacuum molding of polymer composite panels in the exemplary embodiment consists of a 1.5 mm thick sheet of rubber compound based on butyl rubber with a crosslinking degree of 80% crosslinks, ductility 550%, hardness 50 ShA and temperature resistance up to 140 ° C .

Example 2

The pressure diaphragm for vacuum molding of polymer composite panels in the exemplary embodiment consists of a 1 mm thick sheet of a halobutyl rubber based rubber composition having a degree of crosslinking of 85% crosslinks, ductility 550%, hardness 50 ShA and temperature resistance up to 180 ° C.

Example 3

The pressure diaphragm for the vacuum molding of polymer composite panels in the exemplary embodiment consists of a 1 mm thick sheet of a chloroprene rubber blend having a degree of crosslinking of 80% crosslinks, an elongation of 600%, a hardness of 60 ShA and a temperature resistance of up to 130 ° C.

Example 4

The pressure diaphragm for the vacuum molding of polymer composite panels in the exemplary embodiment consists of a 1 mm thick sheet of a rubber compound based on an EPDM copolymer with a degree of crosslinking of 85% crosslinks, an elongation of 200%, a hardness

ShA and temperature resistance up to 140 ° C.

Claims (7)

PATENT CLAIMS A pressure diaphragm for vacuum molding polymer composite panels to overlap and press a process layer of a molded polymer composite deposited on a molded mold part, characterized in that it consists of a sheet structure having a thickness of 0.5 to 2 mm of a diene based rubber compound. elastomer or diene elastomer blends having a degree of crosslinking of 40-85% crosslinks, ductility 200-800%, hardness 20-70 ShA and temperature resistance up to 130-180 ° C. The pressure membrane according to claim 1, characterized in that it consists of a sheet of 0.5 to 2 mm thickness of a rubber compound based on diene elastomer or a mixture of diene elastomers having a degree of crosslinking of 80 to 90% of cross-links, elongation 500 to 600 %, hardness 50 to 60 ShA and temperature resistance up to 130 to 180 ° C. The pressure membrane according to claim 1 or 2, characterized in that the degree of crosslinking of the rubber mixture gradually increases with repeating the vacuum pressing cycles. A thrust membrane according to claim 1, characterized in that it is a sheet-like structure of gas-impermeable material. The compression membrane of claim 1, wherein the diene elastomer of the membrane rubber is butyl rubber or halobutyl rubber. 6. The pressure membrane of claim 1 wherein the diene elastomer of the membrane rubber is chloroprene rubber. The compression membrane of claim 1, wherein the diene elastomer of the membrane rubber is an EPDM copolymer.