WO2003014198A1 - Method for producing composite parts - Google Patents

Abstract

The invention relates to a method for producing composite parts consisting of a thermoplastic polyamide, in which reinforcement agents are embedded. According to said method, the reinforcement agents are brought into contact with a precondensate of the polyamide, said precondensate having a lower molecular weight and as a result a lower melting viscosity than the polyamide. The precondensate is heated, together with the reinforcement agents, to a temperature in excess of its melting point until the resultant melt perfuses the reinforcement agents and simultaneously condenses to form the polyamide.

Description

 DESCRIPTION

TITLE Process for the production of composite parts

TECHNICAL AREA

The present invention relates to a method for producing composite parts with a thermoplastic polyamide and reinforcing agents embedded therein.

STATE OF THE ART

In known processes of this type, the thermoplastic polymer, usually in powder form, is brought into contact with the reinforcing agents and then melted, so that the reinforcing agents are wetted with the polymer material. After the polymer melt has cooled and solidified, the reinforcing agents are embedded in the polymer material. Polymers such as e.g. Polyether sulfone, polypropylene, polyphenylene sulfide or polyamides.

Problems arise in the known processes, however, particularly when polymers with melting points or glass transition temperatures above 200 ° C., such as the aforementioned polyether sulfone, PEEK or polyamides, have to be used to produce high-temperature-resistant composite parts. Like all polymers, these are highly viscous after melting and the wetting of the reinforcing agents is therefore not guaranteed to a sufficient extent. Therefore, the quality of the composite parts produced is often not sufficient. A lowering of the viscosity for better wetting of the reinforcing agents can be done with the above It is practically impossible to reach polymers by increasing the temperature because, due to their high melting point, the temperature must be chosen so high that there is a risk of oxidation and decomposition if the temperature increases further. An increase in the pressure for better wetting of the reinforcing agents is limited by technical difficulties and the risk of damage to the reinforcing agents.

PRESENTATION OF THE INVENTION

The object of the invention is to provide a method for producing composite parts with a thermoplastic polyamide and reinforcing agents embedded therein, in which the above-mentioned problems are avoided and high-quality composite parts with application temperatures above 180 ° C. can also be produced.

This object is achieved according to the invention in that the reinforcing agents are brought into contact with a pre-condensate (prepolymer) of the polyamide which has a lower molecular weight and therefore a lower melt viscosity than the polyamide and that the pre-condensate in contact with the reinforcing agents exceeds its melting point is heated so far and for so long that the resulting melt can wet the reinforcing agents and at the same time condense to the polyamide.

Because of its lower melt viscosity, the precondensate can wet the reinforcing agents much better and more uniformly than is the case with the fully condensed, high molecular weight polymer. The latter arises only after and / or simultaneously with the wetting of the reinforcing agents in contact with them. With a suitable choice of the pre-condensate it can be achieved that when it melts it is almost as liquid as water and spontaneously wets the reinforcing agent. The then drastically increasing viscosity within possibly only a few seconds then no longer has a detrimental influence on the wetting of the reinforcing agents.

With a comparatively lower melting point of the precondensate compared to the condensed-out polymer (which does not always have to be the case), there is also the advantage that the entire composite material may not have to be heated as high and as a result, temperature-sensitive reinforcing agents (such as natural fibers) can also be used.

The precondensate used is preferably one having a molecular weight in the range from 600 to 3000 g / mol.

Pre-condensates that can be used are those that are partly aromatic, but also completely composed of aliphatic units. Mixtures of partially aromatic precondensates with aliphatic precondensates are also possible.

Among the partially aromatic precondensates, those based on terephthalic acid, isophthalic acid or their mixtures or blends are particularly suitable.

Particularly suitable are those which of

A) terephthalic acid and an aliphatic diamine with 4 to 12 carbon atoms and, if necessary, additionally from

B) isophthalic acid and an aliphatic diamine having 4 to 12 carbon atoms and / or

C) Aliphatic dicarboxylic acid with 4 to 18 carbon atoms and an aliphatic diamine with 4 to 12 carbon atoms and / or

D) a lactam or an aminocarboxylic acid with 6 to 20 carbon atoms are derived. Further details can be found in EP 0 693 515 B1.

Among the aliphatic precondensates, there are in particular those which are straight-chain or branched-chain aliphatic or cycloaliphatic dicarboxylic acid having 6 to 36 carbon atoms such as adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, brassylic acid, trimethyl adipic acid, ice and / or trans-cyclohexane -1, 4- dicarboxylic acids, ice and / or trans-cyclohexane-1,3-dicarboxylic acid and dimethyl fatty acids are derived. Suitable straight-chain or branched-chain aliphatic diamines for the preparation of suitable aliphatic precondensates are those having 4 to 13 carbon atoms, such as hexamethylenediamine (1, 6-diaminohexane), 1, 8-diamino-octaone, 1, 10-diaminodecane, 1, 12-diaminododecane, 1, 4-diaminobutane, 2,2-dimethyl-1, 3-diaminopropane, 2,2,4-and / or 2,4,4-trimethyl-1, 6-diaminohexane ,, 2-methyl-1, 5-diaminopentane, 5-methyl-1, 9-diaminononane.

Suitable cycloaliphatic diamines for the preparation of the precondensates are those having 6-26 carbon atoms, such as ice and / or trans-1,4-diaminocyclohexane, ice or trans-1,3-diaminocyclohexane, ice or trans-1,4- Bis (aminomethyl) cyclohexane, ice or trans-1,3-bis (aminomethyl) cyclohexane, 3 (4), 8 (9) -bis (aminomethyl) tricyclo- [5.2.2.0 ^{2 6} ] -decane, 2 ( 3), 5 (6) - bis (aminomethyl) norbornane, 1, 8-diamino-p-menthan, 3-amino-3,5,5'-trimethylcyclohexylamine, bis- (4-amino-3-methylcyclohexyl) methane, and bis-2,2- (4-aminocyclohexyl) propane.

Suitable lactams or ω-aminocarboxylic acids for the production of suitable aliphatic precondensates are those having 6 to 12 carbon atoms, such as caprolactam, lau nlactam or ω-aminocaproic acid, ω-aminolauic acid and ω-aminoundecanoic acid, and ω-aminononanoic acid.

Suitable aliphatic diamines for the production of suitable aliphatic precondensates are those with 8-26 carbon atoms.

Finally, mixtures or blends of the above-mentioned building blocks, including mixtures or blends of partially aromatic with other partially aromatic, partially aromatic with aliphatic and aliphatic with other aliphatic polyamides, are also suitable.

Depending on the selection and composition of the precondensates, polyamide compositions can be produced which can be assigned to the types homopolyamides, copolyamides, block copolyamides, their blends or their alloys.

Homopolyamides are formed, for example, by using precondensates of types PA 46, PA 66, PA 610, PA 1010, PA 612, PA 912, PA 1212, PA 6, PA 11 and PA 12, and also by using precondensates based on cyclic Diamines / dicarboxylic acids or alkyl-substituted cyclic diamines / dicarboxylic acids. Copolyamides or block copolyamides are formed when using precondensates of types PA 46/6, PA 46/1 1, PA 46/12, PA 46/66, PA 46/6/66, PA 46/69, PA46 / 611, PA 46 / 612, PA 46/1212, PA 6/66, PA 11/66 or PA 12/66, and also of pre-condensates of the type PA 46 with aliphatic cyclic diamines / dicarboxylic acids or corresponding aliphatic alkyl-substituted cyclic diamines / dicarboxylic acids.

The thermoplastic polyamide, the precondensate of which is used, can be partially crystalline and should then have a melting point above 200 ° C., but preferably above 240 ° C. If the polyamide is partially aromatic, melting points above 270 ° C., in particular even above 290 ° C., are preferred. For aliphatic polyamides, the corresponding preferred melting temperatures are 250 ° C and 270 ° C. The melting point and other specific properties such as elasticity, resistance to hydrolysis or impact resistance can be varied within a wide range by selecting and possibly combining different precondensates of the type mentioned.

A wide variety of additives, such as heat or UV stabilizers, antioxidants or impact modifiers, etc. can of course also be used in the context of the invention in a conventional manner.

Reinforcing fibers, in particular carbon fibers, glass fibers, aramid fibers, natural fibers (such as hemp, flax, jute, ramie, cotton fibers) or metal fibers, in the form of single fibers, semi-finished textile products, fabrics or tapes, can be used as reinforcing agents. On the other hand or in addition, non-fibrous reinforcing or filling materials, in particular mineral (e.g. layered silicates) and / or metallic and / or magnetic and / or magnetizable substances, can also be used as reinforcing agents.

The precondensate can be brought into contact with the reinforcing agents by methods known per se, such as:

Powder impregnation (fluidized bed, or electrostatic, or flame spraying, or scatter coating process);

Pastes (suspension impregnation); Flüssigimpregnation; or

Extrusion coating.

The processes can be carried out continuously or batchwise. The process according to the invention results in application products such as, for example, glass or carbon fiber-reinforced reinforcement tapes for crude oil and natural gas production pipes and lines (for example off-shore), reinforcements for buildings and bridges or partial reinforcements for injection molded parts, with composite parts being inserted into an injection mold and subsequently overmolded. The method according to the invention can also be used to produce flat, fiber-reinforced semi-finished products, which can be thermoformed (such as deep drawing, pressing, etc.) to form three-dimensional components in a subsequent step (e.g. structural components in automotive engineering).

In the context of the invention, it is preferred if the precondensation in contact with the reinforcing agent is essentially already in the final form of the product or semi-finished product to be produced. This applies in particular when using high-melting polyamides. However, since the parts resulting from the process according to the invention are thermoplastic, they can in principle also be thermoformed at least to a certain extent in a subsequent step.

EXAMPLE 1: Use of PA 6T / 66 precondensate

The HT2 pre-condensate powder Grivory XE 3774 VK produced by EMS-Chemie AG with a relative viscosity of 1.17 (measured as 0.5% m-cresol solution) is evenly sprinkled on a carbon fiber fabric. The melting point of this pre-condensate is 275 ° C (DSC, 1st heating, 80 min). The carbon fiber fabric is an atlas fabric made of 12K rovings of the type Tenax 5N21 with a basis weight of 440 g / sqm. A weight ratio of 30% precondensate powder to 70% carbon fiber fabric is set.

The tissue thus prepared is placed in a flat steel plate tool preheated to 320 ° C. The cavity is blanketed with nitrogen before the tool is closed. The tool is closed and the prepared tissue is pressed at a pressure of 5 bar for 3 minutes. After cooling to 200 ° C, the impregnated and post-condensed plate is removed. The composite part produced in this way is characterized by complete impregnation of the fibers. The melting point of the resulting polymer is 307 ° C.

EXAMPLE 2: Use of PA 46 precondensate

A powdered PA 46 precondensate powder is sprinkled evenly on a carbon fiber fabric. The melting point of this precondensate is 290 ° C (DSC, 1st heating, 807miπ). The carbon fiber fabric is a 4/1 atlas fabric made of 12K rovings of the type Tenax 5N21 with a basis weight of 440 g / sqm. A weight ratio of 30% precondensate powder to 70% carbon fiber fabric is set.

The tissue thus prepared is placed in a flat steel plate tool preheated to 300 ° C. The cavity is blanketed with nitrogen before the tool is closed. The tool is closed and the prepared tissue is pressed at a pressure of 5 bar for 3 minutes.

After cooling to 200 ° C, the impregnated and post-condensed plate is removed. The composite part produced in this way is characterized by complete impregnation of the fibers. The melting point of the resulting polymer is 290 ° C.

EXAMPLE 3: Use of a Mixture of PA 46 and PA 6T / 66 Pre-Condensates

A 1: 1 mixture of powdered PA 46 pre-condensate (from example 2) and PA 6T / 66 pre-condensate (from example 1) is sprinkled evenly onto a carbon fiber fabric (from example 1). A weight ratio of 30% precondensate powder to 70% carbon fiber fabric is set.

The tissue thus prepared is placed in a flat steel plate tool preheated to 320 ° C. The cavity is blanketed with nitrogen before the tool is closed. The tool is closed and the prepared tissue is pressed at a pressure of 5 bar for 3 minutes. After cooling to 200 ° C, the impregnated and post-condensed plate is removed. The composite part produced in this way is characterized by complete impregnation of the fibers. The melting point of the resulting polymer is 246 ° C and is therefore below the melting point of the two pre-condensate components used.

EXAMPLE 4: Use of PA 6T / 66, continuous process

Starting from an unwinding station, a layer of a reinforcement textile, a 4/1 atlas fabric made of 12K carbon fiber rovings of the type Tenax 5N21 with a basis weight of 440 g / sqm, is drawn off. Using a scattering device, powdered PA 6T / 66 precondensate (from Example 1) with a relative viscosity of 1.17 (measured as a 0.5% m-cresol solution) is uniformly applied to the reinforcing textile. The amount of powder is adjusted via the speed of a needle roller so that a weight ratio of 30% precondensate powder to 70% carbon fiber fabric is achieved. The reinforcement textile prepared in this way then passes through an infrared heating zone covered with nitrogen, at the end of which the material reaches a temperature of 320 ° C. The reinforcing textile with the now liquid pre-condensate is then fed into a double belt press in which the laminate is pressed at a temperature of 320 ° C and a pressure of 5 bar and at the same time post-condensed. In a cooling zone of the double belt press, the laminate is then cooled to 250 ° C under a pressure of 5 bar. The composite material produced in this way is characterized by a complete impregnation of the fibers. Either it is cut into sheets using a cutting device or wound up. The melting point of the resulting matrix polymer is 307 ° C.

Example 5: Solid phase post-condensation of composite parts with PA 6T / 66 pre-condensate

A composite part produced according to Example 1 with a relative viscosity of 1.16 (measured as a 0.5% m-cresol solution) is stored in an oven under a nitrogen atmosphere at 300 ° C. for 1 hour. The solid phase post-condensation that occurs here increases the molecular weight and, in conjunction with this, the viscosity in such a way that the strength of the composite part increases considerably. It was no longer possible to determine the relative viscosity in m-cresol because the sample could no longer be dissolved.

Claims

1. A process for the production of composite parts with at least one thermoplastic polyamide and reinforcing agents embedded therein, characterized in that the reinforcing agents are brought into contact with a precondensate of the polyamide which has a lower molecular weight and, as a result, has a lower melt viscosity than the polyamide, and that the pre-condensate in contact with the reinforcing agents is heated beyond its melting point to such an extent and for such a long time that the resulting melt can wet the reinforcing agents and at the same time condense out to form the polyamide. 2. The method according to claim 1 or 2, characterized in that is used as the pre-condensate of such having a molecular weight in the range of 600 to 3000 g / mol. 3. The method according to any one of claims 1 or 2, characterized in that the precondensate contains partially aromatic and / or aliphatic components. 4. The method according to any one of claims 1-3, characterized in that the precondensate contains one or more of the following components: A) terephthalic acid together with an aliphatic diamine having 4 to 12 carbon atoms; B) isophthalic acid together with an aliphatic diamine having 4 to 12 carbon atoms; C) aliphatic dicarboxylic acid with 4 to 18 carbon atoms together with an aliphatic diamine with 4 to 12 carbon atoms; D) Lactam or aminocarboxylic acid with 6 to 20 carbon atoms. 5. The method according to any one of claims 1-4, characterized in that the polyamide has a melting point above 200 ° C, but preferably above 240 ° C. 6. The method according to claim 5, characterized in that the polyamide is partially aromatic and has a melting point above 270 ° C, but preferably above 290 ° C. 7. The method according to claim 5, characterized in that the polyamide is aliphatic and has a melting point above 250 ° C, but preferably above 270 ° C. 8. The method according to any one of claims 1-7, characterized in that a mixture of precondensates of different polyamides is used, from which a composite matrix is formed when condensing and that this composite matrix has a melting point which is lower than the melting point of each of the polyamides whose precondensates are used in the mixture. 9. The method according to any one of claims 1-8, characterized in that reinforcing fibers, in particular carbon fibers, glass fibers, aramid fibers, natural fibers, or metal fibers, in the form of individual fibers, semi-finished textile products, fabrics or tapes, are used as reinforcing agents. 10. The method according to any one of claims 1-9, characterized in that non-fibrous reinforcing or fillers, in particular mineral and / or metallic and / or magnetic and / or magnetizable substances, are used as reinforcing agents. 11. The method according to any one of claims 1-10, characterized in that the precondensate is brought into contact with the reinforcing agents continuously or discontinuously. 12. The method according to any one of claims 1 - 1 1, characterized in that the precondensate in powder form is brought into contact with the reinforcing agents. 13. The method according to any one of claims 1-12, characterized in that the precondensate is brought into contact with the reinforcing agents in one or more of the following ways: Powder impregnation (fluidized bed sintering, or electrostatic, or flame spraying, or scattering method); Pastes (suspension impregnation); Flüssigimpregnation; - extrusion coating. 14. The method according to any one of claims 1-13, characterized in that the composite parts are thermoformed after the condensation of the precondensate in a subsequent step. 15. The method according to any one of claims 1-14, characterized in that the relative viscosity of the composite parts is additionally increased by solid phase post-condensation. 16. Composite parts, produced by the method according to one of claims 1-15.