DE10059436A1 - Production of laminate materials, useful for rotor blades, of a poly(meth)acrylimide foam core and a fiber reinforced or metal layer, comprises treatment of the surfaces with a 2-6C organic solvent. - Google Patents

Abstract

A process for the production of laminate materials (I), having high peel strength comprising a poly(meth)acrylimide foam core layer and at least one fiber reinforced layer or metal layer, comprises treatment of one or both surfaces to be bonded with a total of at least 25 g/m<2> of a 2-6C organic solvent.

Description

The present invention relates to methods for Manufacture of composite materials with high Peel strength, which is a poly (meth) acrylimide foam having core layer and at least one include fiber reinforced layer.

For different applications Polmethacrylimide foams with fiber-reinforced layers provided to composite materials with excellent Get properties. These composite materials are used, among other things, to manufacture rotor blades used (US 5547629). Furthermore, the association with common thermoplastics described, such as a Lamination of polymethacrylimide foams with Polymethyl methacrylate (EP 736372). Another Application of polymethacrylimide foams succeeds through the incorporation of conductive particles in the foam, whereby this for the absorption of electromagnetic radiation can be used (DE 38 26 469 A1). Applications too for the automotive industry are described (JP 63315229 A2). Other relevant patents are also DE 33 04 882 A, GB 1547978 A, DE 28 22 881, DE 22 35 028 and DE 21 14 524.

Composites can be applied, for example, by application can be obtained from prepregs on the foam. A Criterion for the mechanical stability of the Fiber composite material is the liability between cured prepreg and the foam, the so-called Peel strength.  

It has been found that conventional processes in some particularly interesting combinations of Foam and prepreg are insufficient Peel strength result in failure of the Composite material can lead.

This is especially true for multi-layer prepregs that usually applied in thick stacks. A One example among many is the company's Prepreg M9 Hexcel. Combine this product with one Polyacrylimide foam, for example Rohacell 71 FX Röhm GmbH, so the temperature that is used for Hardening of the prepreg is necessary, only gradually increase. Otherwise, a build-up of heat occur that lead to the destruction of the product would. At high curing temperatures there is a high one Curing speed, which in turn leads to a high Leads to heat inside. Problematic with multilayer Prepregs here is that the inside arises Thermal energy can only drain off insufficiently. Hence is usually a temperature scheme for curing driven, which prevents heat build-up. The so Composites obtained, however, often only show one low peel strength, according to DIN 53295 or ASTM D1781 can be determined. The above Example of Prepreg M9 and Rohacell 71 FX delivers at a usual scheme (RT to 90 ° C: 2.7 K / min. 90 ° C for 45 min. 90 ° C to 120 ° C: 0.7 K / min. 120 ° C for 60 min. 120 ° C to room temperature: 5 K / min) a Peel strength of 9.2 J / m. Such one Composite material can already with medium mechanical Failure.

In light of what is stated and discussed herein State of the art was the task of the present  Invention, process for the production of Composites containing a poly (meth) acrylimide foam having core layer and at least one include fiber reinforced layer make that a composite with improved Lead peel strength.

Another object of the invention was to provide a Process for the production of composite materials create that is easy to do.

In addition, the process should be inexpensive.

Furthermore, it was the task of the present one Invention to provide a method that even with slow heating when using multilayer prepregs may be necessary at one leads to high peel strength of the composite obtained.

These tasks are solved as well as others that not to be called literally, but deriving from the here discussed contexts as a matter of course can be derived or inevitably derived from these result from processes for the production of Composite materials with high peel strength, the a core layer comprising poly (meth) acrylimide foam and comprise at least one fiber-reinforced layer, with all the features of independent claim 1.

Appropriate modifications of the invention Procedures are referred back to claim 1 Subclaims placed under protection.

By treating one or both of the surfaces to be joined with a total of at least 25 g / m ^{2 of} an organic solvent comprising 2 to 6 carbon atoms, it is possible to produce composites which have a core layer comprising poly (meth) acrylimide foam and at least comprise a fiber-reinforced layer or metal layer, which lead to a composite material with improved peel strength.

The following advantages, in particular, are achieved by the measures according to the invention:

• - ¾ The inventive method is simple in the Execution.
• - ¾ The improvement of the peel strength can be without achieved the use of special adhesives will.
• - ¾ By the inventive method, the fiber-reinforced layer particularly firmly on the Core layer applied.
• - To improve the peel strength can Within the scope of the present invention in particular connections harmful to health are dispensed with will.
• - ¾ In the method of the present invention fiber-reinforced layers are also used, which have a multilayer structure.
• - ¾ By the method according to the invention can also fiber-reinforced cover layers firmly with the Foam core can be connected, which is low Have thermal conductivity.

In the process of the present invention, at least one of the two surfaces to be bonded is treated with at least 25 g / m ^{2 of} an organic solvent comprising 2 to 6 carbon atoms.

Accordingly, either the surface of the Polyacrylimidschaumes or the surface of the fiber reinforced layer with the solvent in Be brought in contact. Both can also Surfaces are treated with the solvent.

A solvent that can be used in the process has 2 to 6, preferably 2 to 4 carbon atoms. Without that this should result in a restriction special embodiments of the solvent Boiling point at normal pressure in the range from 40 to 150 ° C, preferably 50 to 100 ° C.

These include acetone, butanol, Ethyl acetate, ethanol, isopropanol and tetrahydrofuran, Acetone, ethanol and isopropanol are preferred. These solvents can be used individually or as a mixture be used. In addition, the Common solvent additives, for example the shelf life and the application behavior improve, contain.

According to the invention, at least 25 g / m ^{2 of} one or more of the solvents described above must be used to treat the surface. In particular embodiments, 30 to 150, preferably 40 to 100 g / m ² are used.

The type of surface treatment itself is not critical. In general, everyone can Order types are used that also include paints be applied. So one or both of them can connecting surfaces are sprayed. About that In addition, the surfaces can be mixed with the solvent be smeared. Furthermore, the solvent can also be applied by doctor blade or roller.

In special configurations of the invention The process is allowed to solvent for at least 1 s and at most 10 min. preferably at least 10 s and at most 2 min and particularly preferably at least 20 s and act for a maximum of 45 s before touching the surface the core layer with the surface of the fiber reinforced Layer connects.

The relevant for the method of the invention Core layers have poly (meth) acrylimide foam.

The spelling in brackets should be a mark optional feature. 50 means for example (meth) acrylic acrylic, methacrylic and Mixtures of the two.

The poly (meth) acrylimide foams obtainable from the compositions according to the invention have recurring units which can be represented by formula (I)

wherein
R ¹ and R ^{2 are} identical or different hydrogen or a methyl group and R ^{3 is} hydrogen or an alkyl or aryl radical having up to 20 carbon atoms.

Units of structure (I) preferably form more than 30% by weight, particularly preferably more than 50% by weight and very particularly preferably more than 80% by weight of the Poly (meth) acrylimide foam.

The production of poly (meth) acrylimide Rigid foams are known per se and for example in GB-PS 1 078 425, GB-PS 1 045 229, DE-PS 18 17 156 (= US-PS 3 627 711) or DE-PS 27 26 259 (= US-PS 4 139 685) disclosed.

The units of structural formula (I) among other things when heated to 150 to 250 ° C neighboring units of (meth) acrylic acid and (Meth) acrylonitrile by a cyclizing Form isomerization reaction (cf. DE-C 18 17 156, DE-C 27 26 259, EP-B 146 892). Usually first a preliminary product by polymerizing the Monomers in the presence of a radical initiator low temperatures, e.g. B. 30 to 60 ° C with Post-heating to 60 to 120 ° C generated, then by Heating to approx. 180 to 250 ° C by means of an included Foaming agent is foamed (see EP-B 356 714).

For this purpose, for example, a copolymer can first be used are formed, which (meth) acrylic acid and (Meth) acrylonitrile, preferably in a molar ratio between 1: 3 and 3: 1.

In addition, these copolymers can further Contain monomer units, for example Esters of acrylic or methacrylic acid, especially with low alcohols with 1-4 carbon atoms, styrene, Maleic acid or its anhydride, itaconic acid or its  Anhydride, vinyl pyrrolidone, vinyl chloride or Result in vinylidene chloride. The proportion of comonomers, that are difficult or difficult to cyclize, should be 30% by weight, preferably 20% by weight and particularly preferably 10% by weight, based on the weight of the Monomers, do not exceed.

Other known monomers can also be known Way small amounts of crosslinking agents, such as. B. Allyl acrylate, allyl methacrylate, ethylene glycol diacrylate or -dimethacrylate or polyvalent metal salts of Acrylic or methacrylic acid, such as magnesium methacrylate can be used advantageously. The proportions of these Crosslinkers are often in the range from 0.005 to 5 wt .-%, based on the total amount polymerizable monomers.

Metal salt additives can also be used, which often reduce smoke gas. These include including the acrylates or methacrylates of the Alkali or alkaline earth metals or zinc, zircon or lead. Na, K, Zn and Ca are preferred (Meth) acrylate. Amounts of 2 to 5 parts by weight of the Monomers significantly reduce the Flue gas density during fire testing in accordance with FAR 25.853a.

As polymerization initiators are in themselves for the polymerization of (meth) acrylates customary related, for example azo compounds, such as Azodiisobutyronitrile, as well as peroxides, such as Dibenzoyl peroxide or dilauroyl peroxide, or also other peroxide compounds, such as t-butyl peroctanoate or perketals, as well if necessary, redox initiators (cf. for example H. Rauch-Puntigam, Th. Völker, Acryl- and methacrylic compounds, Springer, Heidelberg, 1967 or Kirk-Othmer, Encyclopedia of Chemical Technology,  Vol. 1, pages 286 ff, John Wiley & Sons, New York, 1978). The polymerization initiators are preferred in amounts of 0.01 to 0.3 wt .-%, based on the Starting materials used.

It can also be advantageous to use polymerization initiators with different decay properties regarding Combine time and temperature. Is well suited e.g. B. the simultaneous use of tert-butyl perpivalate, tert-butyl perbenzoate and tert-butyl per- 2-ethylhexanoate or of tert-butyl perbenzoate, 2,2-azobisiso-2,4-dimethylvaleronitrile, 2,2-azobisisobutyronitrile and di-tert-butyl peroxide.

The polymerization is preferably carried out via variants substance polymerization, such as this Chamber procedure mentioned, without being limited to this be.

The weight average molecular weight M _{w of} the polymers is preferably greater than 10 ⁶ g / mol, in particular greater than 3 × 10 ⁶ g / mol, without any intention that this should impose a restriction.

For foaming the copolymer during Conversion into an imide group-containing polymer serve in known blowing agent at 150 to 250 ° C. form a gas phase through decomposition or evaporation. Propellants with an amide structure, such as urea, Monomethyl or N, N'-dimethylurea, formamide or Monomethylformamide, put on decomposition ammonia or Amines free, which lead to the additional formation of Imid groups can contribute. However, it can also nitrogen-free blowing agents such as formic acid, water or monohydric aliphatic alcohols with 3 to 8 carbon atoms, such as 1-propanol, 2-propanol, n-butan-1-ol, n-butan-2-ol, isobutan-1-ol, isobutan-2-ol, pentanols  and / or hexanols can be used. The one used The amount of blowing agent depends on the desired amount Foam density, the blowing agents in the Reaction batch usually in amounts of about 0.5 to 15% by weight, based on the monomers used, be used.

Furthermore, the preliminary products can be customary Contain additives. These include, among others Antistatic agents, antioxidants, mold release agents, Lubricants, dyes, flame retardants, Flow improvers, fillers, light stabilizers and organic phosphorus compounds such as phosphites or phosphonates, pigments, weather protection agents and plasticizers.

Conductive particles that are electrostatic Preventing charging of the foams are one another class of preferred additives. For this include metal and soot particles, among others may be present as fibers with a size in the range of 10 nm and 10 mm, as described in EP 0 356 714 A1 is described.

A very particularly preferred polymethacrylimide foam that can be used can be obtained, for example, by the following steps:

• 1. Production of a polymer plate by radical polymerization of a composition consisting of
  • a) a monomer mixture of 20-60 wt .-% methacrylonitrile, 80-40 wt .-% methacrylic acid and optionally up to 20 wt .-%, based on the sum of methacrylic acid and methacrylonitrile, other monofunctional, vinylically unsaturated monomers
  • b) 0.5-15% by weight of a blowing agent mixture of formamide or monomethylformamide and a monohydric aliphatic alcohol with 3-8 carbon atoms in the molecule
  • c) a network system, which consists of
    • 1. (c.1) 0.005-5% by weight of a free-radically polymerizable vinylically unsaturated compound with at least 2 double bonds in the molecule and
    • 2. (c.2) 1-5 wt .-% magnesium oxide dissolved in the monomer mixture
  • d) an initiator system
  • e) usual additives
• 2. This mixture is several days at 30 to 45 ° C. in one of two 50.50 cm glass plates and a 2.2 cm thick edge seal Chamber polymerized. Then that will Polymer for final polymethacrylimide polymerization about 20 h from 40 ° C to 130 ° C Tempering program subjected. The next one Foaming takes place at 200 for a few hours up to 250 ° C.

Polymethacrylimide with high heat resistance can also by implementing Polymethyl methacrylate or its copolymers with primary amines are obtained as well can be used according to the invention. Representative of  the variety of examples of these polymer analogs Imidation may be mentioned: US 4,246,374, EP 216,505 A2, EP 860 821. High heat resistance can be either by using arylamines (JP 05222119 A2) or by using achieve special comonomers (EP 561 230 A2, EP 577 002 A1). However, none of these reactions result Foams, but solid polymers that are used to obtain a Foam in a separate second step have to be foamed. For this too are in the Techniques known.

Rigid poly (meth) acrylimide foams can also can be obtained commercially, such as ®Rohacell from Röhm GmbH, in different densities and sizes is available.

The density of the poly (meth) acrylimide foam is preferably in the range from 20 kg / m ³ to 320 kg / m ³ , particularly preferably in the range from 50 to 110 kg / m ³ .

Without this being intended to impose a restriction, the thickness of the core layer is in the range from 1 to 200 mm, especially in the range from 5 to 100 and whole particularly preferably in the range from 10 to 70 mm.

The core layer can additionally additional inside Have layers. However, in the process of present invention a poly (meth) acrylimide foam connected with a fiber-reinforced layer. In special embodiments of the invention However, a core layer is used, which consists of poly (meth) acrylimide foam.

Any known one can be used as the fiber-reinforced layer flat structures are used, which in the  Production of composite materials necessary Processing parameters such as pressure and temperature, is stable. Can also be used as a fiber-reinforced layer Lanes are used that are multi-layered Have structure.

These include a. for example fiber reinforced Foils made of polypropylene, polyester, polyamide, Polyurethane, polyvinyl chloride and / or Contain polymethyl (meth) acrylate.

The fiber reinforced layer can also be hardened by known fiber-containing resins, for example Epoxy resins (EP resins), methacrylate resins (MA resins), unsaturated polyester resins (UP resins), phenolic resins, Isocyanate resins, bismaleimide resins and phenacrylate resins (PHA resins) can be obtained.

As fiber reinforcement come among other things carbon fibers, Glass fibers, aramid fibers, polypropylene fibers, Polyester fibers, polyamide fibers, polyurethane fibers, Polymethyl (meth) acrylate fibers Polyvinyl chloride fibers and / or metal fibers.

Prepregs, for example, may also be preferred SMCs (sheet molding compounds) belong, used to be a fiber reinforced on the core layer To get layer. SMC and prepregs are included curable plastics pre-impregnated sheets, mostly Glass fiber mats, glass filament fabrics or carbon fibers and / or rovings containing aramid fibers, which by Hot pressing into molded parts or semi-finished products can be. The SMCs that can be used include especially SMC-R (SMC with arbitrarily oriented Fibers), SMC-O (SMC with oriented fibers), SMC-CR (SMC with fibers that are partially oriented), XMC  (SMC with reticulated fiber reinforcement) and HMC (SMC with high fiber content).

These materials are known per se and for example in Ullmann's, Encyclopedia of Industrial Chemistry 5th edition, keyword "Fabrication of Polymer Composites ").

In addition to a fiber-reinforced layer, too Layers of metal by the process of present invention particularly firmly with the Core layer to be connected. These include under other thin foils or sheets made of aluminum. The Metal layer can be used alone or together with a fiber reinforced layer used to make a Manufacture composite. Particularly preferred Metal layers include so-called Aluminum prepregs.

Joining the core layer with the fiber reinforced Layer or the metal layer after treatment with the organic solvent depends on the type the layer to be applied. Appropriate procedures are known per se.

This allows composite materials that have a core Poly (meth) acrylimide foam and a fiber reinforced Have layer or a metal layer in generally obtained by so-called hot pressing processes will. These procedures are widely used in the professional world known, with special embodiments, such as for example double belt presses, SMC presses and GMT Presses are covered by the invention.

To further solidify the composite material, the core layer is compressed during hot pressing.  

For this purpose, spacers, so-called attacks can be used. These facilitate the setting of a desired one Degree of compaction of the core layer without this the invention is to be restricted.

An adhesive can also be used to improve adhesion be used after treatment of the surface be applied with the organic solvent can. Depending on the material of the fiber-reinforced layer however, this is not necessary.

Can be used to manufacture the composite for example an SMC or prepreg layer on the appropriately dimensioned foam sheet within a form appropriate to the weight Quantity placed and press pressure applied.

Typical working conditions in which the prepregs or SMCs begin to flow and harden are pressures of more than 1 N / mm ² and temperatures in the range from 60 to 180 ° C. These parameters can also be used as a step gradient to avoid heat build-up. The pressing time is usually 5 minutes-6 hours, depending on the type of fiber-reinforced layer. A particularly useful range is between 10 and 120 minutes.

In addition, the aforementioned resins and Fiber reinforcements also manually on the Poly (meth) acrylimide foam can be applied. Here alternate between resin layers and fiber webs hung up. After applying the fiber reinforced Resin layer, the resin is hardened in a known manner. Corresponding systems can, for example, by M. u. H.  from Linden GmbH, Postfach 100543, D-46465 Wesel / Rhine can be obtained under the name West System.

The thickness of the cover layer is preferably in the range from 0.1 to 100 mm, preferably in the range from 0.5 to 50 mm and very particularly preferably in the range from 1 to 5 mm.

Preferred embodiments of the invention Composites that can be produced have two Cover layers on the one with the core layer Form sandwich structure.

The manufactured according to the inventive method Composites have excellent mechanical Properties. For example, the Peel strength according to DIN 53295 10 Nmm / mm or more, preferably more than 15 Nmm / mm.

Furthermore, the bending strength is according to DIN 53423 with values of 2 MPa or more, in particular greater than 2.3 MPa surprisingly high. Also the Bending stiffness according to DIN 53 293 shows values of 8 MPa or more, especially greater than 10 MPa.

The invention is illustrated below by examples and Comparative examples explained in more detail without the Invention to be limited to these examples.

example 1

A prepreg from Hexcel (type M9) was placed on a polymethacrylimide foam sheet with a density of 70 kg / m ³ (Röhm GmbH, ROHACELL 71FX), which had been coated with 50 g / m ² acetone 30 s beforehand. The workpiece prepared in this way was heated to 90 ° C at 2.7 ° C / min without pressure, further heated to 120 ° C after 0.7 min at 0.7 ° C / min and to 40 after 5 min at 5 ° C / min ° C cooled. The composite material produced in this way had a peel strength according to DIN 53295, ASTM D1781 of 16.1 J / m.

Example 2

The procedure was as in Example 1, only that instead Acetone isopropanol was used. The so made Composite showed a peel strength according to DIN 53295, ASTM D1781 of 14.3 J / m.

Example 3

The procedure was as in Example 1, only that instead Acetone ethanol was used. The so made Composite showed a peel strength according to DIN 53295, ASTM D1781 of 12.6 J / m.

Comparative Example 1

A prepreg from Hexcel (type M9) was placed on a polymethacrylimide foam sheet with a density of 70 kg / m ³ (Röhm GmbH, ROHACELL 71FX). The workpiece prepared in this way was heated to 90 ° C at 2.7 ° C / min without pressure, further heated to 120 ° C after 0.7 min at 0.7 ° C / min and to 40 after 5 min at 5 ° C / min ° C cooled. The composite material produced in this way had a peel strength according to DIN 53295, ASTM D1781 of 9.2 J / m.

Comparative Example 2

A prepreg from Hexcel (type M9) was placed on a polymethacrylimide foam sheet with a density of 70 kg / m ³ (Röhm GmbH, ROHACELL 71IG). The workpiece prepared in this way was heated to 90 ° C at 2.7 ° C / min without pressure, further heated to 120 ° C after 0.7 min at 0.7 ° C / min and to 40 after 5 min at 5 ° C / min ° C cooled. The composite material produced in this way had a peel strength according to DIN 53295, ASTM D1781 of 8.6 J / m.

Claims (10)

1. A process for the production of composite materials with high peel strength, which comprise a poly (meth) acrylimide foam core layer and at least one fiber-reinforced layer or metal layer, characterized in that one or both of the surfaces to be joined with a total of at least 25 g / m ^{2 of} a treated organic solvent comprising 2 to 6 carbon atoms. 2. The method according to claim 1, characterized in that one uses 40 to 100 g / m ^{2 of} the organic solvent. 3. The method according to claim 1 or 2, characterized in that the solvent at least 1 s and at most 10 min. prefers at least 10 s and at most 2 min and especially preferably at least 20 s and at most 45 s Allow to take effect before the core layer and the fiber-reinforced layer connects. 4. Method according to one or more of the previous claims, characterized in that acetone, butanol, ethyl acetate, ethanol, Isopropanol or tetrahydrofuran as a solvent to treat the surface to be joined starts.   5. Method according to one or more of the previous claims, characterized in that one or more as a fiber-reinforced layer Uses prepregs. 6. Method according to one or more of the previous claims, characterized in that one uses aluminum prepregs as the metal layer. 7. Method according to one or more of the previous claims, characterized in that you use a core layer that consists of Poly (meth) acrylimide foam consists. 6. Method according to one or more of the previous claims, characterized in that the fiber-reinforced layer of carbon fibers, Glass fibers, aramid fibers, polypropylene fibers, Polyester fibers, polyamide fibers, Polyurethane fibers, polymethyl (meth) acrylate fibers Polyvinyl chloride fibers and / or metal fibers contains. 9. Method according to one or more of the previous claims, characterized in that one uses two fiber-reinforced layers in order to to get a sandwich structure. 10. Method according to one or more of the previous claims, characterized in that  you use a fiber-reinforced layer that has a multilayer structure.