DE102009027244A1 - Process for producing a foam part from crosslinked poly (meth) acrylates and the foam and its use - Google Patents

Abstract

The invention relates to a process for producing a foam part from crosslinked poly (meth) acrylates, characterized by the following steps: a. Polymerization of a polymerizable monomer mixture which consists essentially of non-crosslinking (meth) acrylate monomers, crosslinkers and an initiator system, in the Gußpolymerisationsverfahren to a pre-polymer, b. Loading the prepolymer with an inert gas as blowing agent at a pressure in the range of 2 to 200 bar, c. Lowering the pressure and expanding the pre-polyperisate to the foam part at a temperature at which the propellant-loaded pre-polymerate is foamable, d. Fixation of the foam part by lowering the temperature. The invention further relates to the foam part and its uses.

Description

Field of the invention

The Invention relates to a method for producing a foam part, in particular a closed-cell foam part, by expansion from prepolymers of crosslinked poly (meth) acrylates, which in the Gußpolymerisationsverfahren be prepared.

State of the art

Plastic rigid foams have been known for a long time and are widely used because of their excellent mechanical properties and low weight, especially in the manufacture of laminates, laminates, composites or foam composites. Here are often long fiber reinforced cover layers z. B. made of carbon fibers with the help of adhesive resins form-fitting and permanently connected to core materials made of hard foams. As hard foams z. Poly (meth) acrylimide foams under the brand ROHACELL ^® from Evonik put on the market. For example, coating materials are used as stiff, lightweight components in aircraft construction, in shipbuilding, in the automotive industry or in the wings of wind power plants.

autoclave for the production of foams are known in principle. Resulting foams However, they are generally not mechanically stable enough as core materials be used for heavily loaded coating materials to be able to.

Task and solution

It was seen as a task to develop a method that makes it possible Produce foam parts with good mechanical properties, the low material usage cost-effective production allows. In particular, a particularly fine control the size and uniformity the formation of the pore structure be possible. The procedure should a particularly uniform distribution of the polymer over allow the cell walls of the foamed plastic.

• a. Polymerisation einer polymerisierbaren Monomermischung, die sich im Wesentlichen aus nicht vernetzenden (Meth)acrylatmonomeren, Vernetzern und einem Initiatorsystem zusammensetzt, im Gusspolymerisationsverfahren zu einem Pre-Polymerisat,
• b. Beladung des Pre-Polymerisats mit einem inerten Gas als Treibmittel bei einem Druck im Bereich von 2 bis 200 bar,
• c. Absenkung des Drucks und Expansion des Pre-Polymerisats zum Schaumstoffteil bei einer Temperatur, bei der das Treibmittelbeladene Pre-Polymerisat schäumbar ist,
• d. Fixierung des Schaumstoffteils durch Absenken der Temperatur

The task is solved by a
Process for producing a foam part from crosslinked poly (meth) acrylates, characterized by the following steps

• a. Polymerization of a polymerisable monomer mixture, which consists essentially of non-crosslinking (meth) acrylate monomers, crosslinkers and an initiator system, in the casting polymerization process to a prepolymer,
• b. Loading of the prepolymer with an inert gas as propellant at a pressure in the range of 2 to 200 bar,
• c. Lowering the pressure and expanding the prepolymer to the foam part at a temperature at which the blowing agent-loaded prepolymer is foamable,
• d. Fixation of the foam part by lowering the temperature

Embodiment of the invention

The Invention relates to a method for producing a foam part, in particular a closed-cell foam part, by expansion from prepolymers of crosslinked poly (meth) acrylates, which in the Gußpolymerisationsverfahren be prepared.

Poly (meth) acrylates

Poly (meth) acrylates For the purposes of the invention, polymers which are predominantly z. At least 60, at least 70, at least 80, at least 90 wt .-%, or entirely of polymerized acrylates and / or methacrylates and possibly also to a lesser extent comonomers which are not (meth) acrylates. Under (Meth) acrylates are both acrylic acid and methacrylic acid and their derivatives.

Pre-polymer

The term prepolymer within the meaning of the invention denotes the claim according to the polyme rized monomer mixture, which is present in the form of a solid plastic part before the foaming. The prepolymer is thus an intermediate polymer or a non (not yet) foamed plastic body.

Crosslinked poly (meth) acrylates

networked Poly (meth) acrylates are, in particular, crosslinked polymethyl (meth) acrylates or crosslinked poly (meth) acrylimides.

Prepolymer of crosslinked polymethyl (meth) acrylates

Pre-polymers from crosslinked polymethyl (meth) acrylates in the context of the invention are obtainable by polymerization of a polymerizable Monomer mixture, which consists essentially of Methylmethacylat as non-crosslinking (meth) acrylate monomers, crosslinkers and a Initiator system composed in Gußpolymerisationsverfahren.

in the Substantially means that the substances mentioned for the production of a polymer are obligatory and that except the substances mentioned further optional components or additives but the character of the polymethyl (meth) acrylate do not significantly affect. In a preferred embodiment can continue blowing agents that are not inert gases, additionally present in the polymerizable monomer mixture be.

A suitable polymerizable monomer mixture for polymethyl (meth) acrylates may for example consist of:
At least 60, at least 70, at least 80, at least 90% by weight, methyl methacrylate, and
up to 40, up to 30 up to 20 up to 10% by weight of other vinylically unsaturated non-crosslinking monomers,
0.01-10 wt .-% crosslinkers
0.01 to 5 wt .-% of polymerization initiators and
0 to 20 wt .-% of conventional additives
0 to 10 wt .-% further blowing agents

in principle complement all components contained to 100 wt .-%

Other vinylic unsaturated, non-crosslinking monomers for polymethyl (meth) acrylates

suitable other vinylically unsaturated non-crosslinking monomers are z. As methacrylic acid and esters of methacrylic acid (eg, ethyl methacrylate, butyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate), Acrylic acid and esters of acrylic acid (eg, methyl acrylate, Ethyl acrylate, butyl acrylate, hexyl acrylate, cyclohexyl acrylate) or Styrene and styrene derivatives such as α-methylstyrene or p-methylstyrene, as well as methacrylonitrile and acrylonitrile, methacrylamide and acrylamide and substituted methacrylamides and substituted acrylamides.

Crosslinker for polymethyl (meth) acrylates

Suitable crosslinkers are, for example, (meth) acrylic esters of diols, such as ethylene glycol dimethacrylate or 1,4-butanediol dimethacrylate, aromatic compounds having two vinyl or allyl groups, such as divinylbenzene, or other crosslinkers having two ethylenically unsaturated, radically polymerizable radicals, such. B. allyl methacrylate used. Examples of crosslinkers containing three or more unsaturated, radically polymerizable groups, such as allyl groups or (meth) acrylic groups, include triallyl cyanurate, trimethylolpropane triacrylate and trimethacrylate, and pentaerythritol tetraacrylate and tetramethacrylate. Other examples are z. In US 4,513,118 specified.

When further group are ionic crosslinkers into consideration. these are polyvalent metal cations, the ionic bridges between form the acid groups of the copolymers. examples are including the acrylates or methacrylates of alkaline earth metals or zinc. Zn and Mg (meth) acrylates are preferred. The (meth) acrylate salts can also be resolved by dissolving z. From ZnO or MgO be prepared in the monomer mixture. The use of ionic Crosslinkers assume that acid group-containing monomers, z. As acrylic acid or preferably methacrylic acid be copolymerized with.

Polymerization initiators for Polymethyl (meth) acrylates

The Polymerization is generally carried out with known free-radical initiators started. Among the preferred initiators include Others well-known in the art Azoinitiatoren how AIBN and 1,1-azobiscyclohexanecarbonitrile, as well as peroxy compounds, such as methyl ethyl ketone peroxide, acetylacetone peroxide, dilauryl peroxide, Di-tert-butyl peroxide, tert-butyl per-2-ethylhexanoate, ketone peroxide, Methyl isobutyl ketone peroxide, cyclohexanone peroxide, dibenzoyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxyisopropyl carbonate, 2,5-bis (2-ethylhexanoylperoxy) -2,5-dimethylhexane, tert-butyl peroxy-2-ethylhexanoate, tert-butylperoxy-3,5,5-trimethylhexanoate, Dicumyl peroxide, 1,1-bis (tert-butylperoxy) cyclohexane, 1,1-bis (tert-butylperoxy) 3,3,5-trimethylcyclohexane, Cumyl hydroperoxide, tert-butyl hydroperoxide, bis (4-tert-butylcyclohexyl) peroxydicarbonate, Mixtures of two or more of the aforementioned compounds with each other and mixtures of the aforementioned compounds with those not mentioned Compounds that can also form radicals.

These Compounds are commonly found in an amount of 0.01 to 5 wt .-%, preferably from 0.5 to 3 wt .-%, by weight the monomers used.

Usual additives for Polymethyl (meth) acrylates

the Those skilled in the art are numerous suitable, common auxiliary or Additives known. These include, for example, antistatic agents, Antioxidants, mold release agents, flame retardants, lubricants, Dyes, flow improvers, fillers, light stabilizers, UV absorbers and organic phosphorus compounds, such as phosphites or Phosphonates, pigments, weathering agents and plasticizers.

Further blowing agents for polymethyl (meth) acrylates

In In another embodiment, the polymerizable Monomer mixture additionally contain other propellants. The other blowing agents are different from the inert gases, which are also used in the context of the invention as a propellant become. However, the polymerizable monomer mixture is preferred no or only insignificant amounts added further blowing agents.

When Propellants can z. As the following compounds or mixtures be used: formamide, formic acid, urea, itaconic acid, Citric acid, dicyandiamide, water, monoalkylureas, Dimethylurea, 5,5'-azo-bis-5-ethyl-1,3-dioxane, 2,2'-azo-bis-isobutyric acid butylamide, 2,2'-azo-bis-isobutyric acid N-diethylamide, 2,2 ', 4,4,4', 4'-hexamethyl-2,2'-azopentane, 2,2'-azo-bis-2-methyl-propane, dimethyl carbonate, di-tert-butycarbonate, Acetone cyanohydrate carbonate, oxi-isobutyric acid methyl ester carbonate, N-methyl urethane, N-ethyl urethane, N-tert-butyl urethane, urethane, oxalic acid, Maleic acid, oxi-isobutyric acid, malonic acid, Cyanformamide, dimethylmaleic acid, tetraacetate of methanetetracarboxylate, Oxamide of n-butyl, trimethyl methane tricarboxylate, Triethyl methane tricarboxylate, and monovalent Alcohols of 3-8 carbon atoms such. Propanol-1, propanol-2, Butanol-1, butanol-2, tert-butanol and iso-butanol.

When further, einpolymerisierendes propellant can tert-butyl methacrylate or tert-butyl acrylate. Split as comonomers used these compounds when heating the pre-polymer the blowing agent Isobutene off.

Prepolymer of crosslinked poly (meth) acrylimides

Pre-polymers arise from crosslinked poly (meth) acrylimides in the context of the invention by thermal conversion of crosslinked copolymers of methacrylic acid and methacrylonitrile. In the thermal conversion will be about 60 to 80% of the methacrylic and methacrylonitrile units converted to cyclic imide structures. It is found in the polymer unreacted methacrylic acid and methacrylonitrile units, as well as additionally cyclic anhydride structures, polyimine ladder polymer units. The crosslinked copolymers of methacrylic acid and methacrylonitrile are obtained by polymerization in Gußpolymerisationsverfahren a polymerizable monomer mixture which is substantially of methacrylic acid and methacrylonitrile as non-crosslinking (Meth) acrylate monomers, crosslinkers and an initiator system composed.

Essentially means that the said substances are obligatory for the preparation of a polymer and that in addition to the substances mentioned other optional components or additives may be included, but which do not significantly affect the character of the copolymer or of the resulting poly (meth) acrylimides. In a preferred embodiment, propellants, which are inert gases, may additionally be present in the polymerizable monomer mixture.

A suitable polymerizable monomer mixture for poly (meth) acrylimides may for example consist of: 30-70 % By weight of methacrylic acid, 30-60 % By weight of methacrylonitrile, 0-30% by weight of further non-crosslinking, vinylically unsaturated monomers, 0.01-10 % By weight crosslinker, 0.01 to 2 % By weight of polymerization initiators and 0 to 20 Wt .-% of conventional additives 0 to 10 Wt .-% further blowing agents

in principle complement all components contained to 100 wt .-%

Non-crosslinking (meth) acrylate monomers for poly (meth) acrylimides

30 to 70% by weight of methacrylic acid and from 30 to 60% by weight of methacrylonitrile form as the most important monomers the basic structure of the later Poly (meth) acrylimide, which consists of the original polymer, at low temperature of z. B. 30 to 60 ° C in the casting process is obtained, at higher temperatures, eg. B in the area from 150 to 250 ° C, by reaction of neighboring units methacrylic acid and methacrylonitrile cyclic imide structures training, emerges.

Except Methacrylic acid and methacrylonitrile may be optional 0 to 30 wt .-% further vinylically unsaturated monomers be included: acrylic or methacrylic acid and their Esters with lower alcohols with 1-4 C atoms, styrene, maleic acid or their anhydride, itaconic acid or its anhydride, vinylpyrrolidone, Vinyl chloride and / or vinylidene chloride. The proportion of comonomers, which do not or only with great difficulty cyclize to anhydride or imide should be 30 wt .-%, preferably 20 wt .-% and particularly preferably 10 wt .-%, based on the weight of the monomers, not exceed.

Crosslinker for poly (meth) acrylimides

The Formulations must be added small amounts of crosslinker. Suitable amounts are for. From 0.01 to 10, 0.01 to 2, 0.01 to 0.5 Wt .-% based on the total weight of the monomer mixture.

A Light crosslinking stabilizes the foam during the process Foaming process and thus allows the production of homogeneous foams. At the same time, the heat resistance and improves the creep behavior of the foam by crosslinking agents.

Possible Crosslinkers can be divided into two groups: covalent Crosslinkers and ionic crosslinkers.

covalent Crosslinkers are copolymerizable polyunsaturated Links. As such monomers z. B. allyl acrylate, Allyl methacrylate, allylacrylamide, allylmethacrylamide, methylene-bis-acrylamide or methacrylamide, diethylene bis (allyl carbonate), ethylene glycol diacrylate or dimethacrylate, diethylene glycol diacrylate or dimethacrylate, Triethylene glycol diacrylate or dimethacrylate, tetraethylene glycol diacrylate or dimethacrylate, tripropylene glycol diacrylate or dimethacrylate, 1,3-butanediol diacrylate or dimethacrylate, 1,4-butanediol diacrylate or dimethacrylate, neopentyl diol diacrylate or dimethacrylate, Hexanediol-1,6-diacrylate or dimethacrylate, trimethylolpropane diacrylate or dimethacrylate, trimethylolpropane triacrylate or trimethacrylate, Pentaerythritol triacrylate or trimethacrylate, pentaerythritol tetraacrylate or tetramethacrylate, the pentaerythritol derivatives in each case also, if necessary as a technical mixture of tri- and tetrafunctional compounds, and triallyl cyanurate or triallyl isocyanurate.

When further group are ionic crosslinkers into consideration. these are polyvalent metal cations, the ionic bridges between form the acid groups of the copolymers. examples are including the acrylates or methacrylates of alkaline earth metals or zinc. Zn and Mg (meth) acrylates are preferred. The (meth) acrylate salts can also be resolved by dissolving z. From ZnO or MgO be prepared in the monomer mixture. The use of ionic Crosslinkers assume that acid group-containing monomers, z. As acrylic acid or preferably methacrylic acid be copolymerized with.

Polymerization initiators for Poly (meth) acrylimides

As initiators, compounds and initiator systems that can initiate radical polymerizations are used. Known classes of compounds are peroxides, hydroperoxides, peroxodisulfates, percarbonates, perketals, peroxyesters, hydrogen peroxide and azo compounds. Examples of initiators are hydrogen peroxide, dibenzoyl peroxide, dicyclohexyl peroxodicarbonate, dilauryl peroxide, methyl ethyl ketone peroxide, acetyl acetone peroxide, di-tert-butyl peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, tert-butyl peroctanoate, tert-butyl per-2-ethylhexanoate, tert-butyl perodecanoate, tert-amyl perpivalate, tert-butyl peroxide. Butyl perpivalate, tert-butyl perbenzoate, lithium, sodium, potassium and ammonium peroxodisulfate, azoisobutyronitrile, 2,2-azobisiso-2,4-dimethylvaleronitrile, 2,2-azobisisobutyronitrile, 2,2'-azobis (2) amidinopropane) dihydrochloride, 2- (carbamoylazo) isobutyronitrile and 4,4'-azobis (cyanovaleric acid). Likewise suitable are redox initiators ( H. Rauch-Puntigam, Th. Völker, acrylic and methacrylic compounds, Springer, Heidelberg, 1967 or Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 1, pp. 286 et seq., John Wiley & Sons, 1 New York, 1978 ). It may be beneficial to combine initiators and initiator systems having different disintegration properties with respect to time and temperature. The initiators are preferably used in amounts of from 0.01 to 2% by weight, particularly preferably from 0.15 to 1.5% by weight, based on the total weight of the monomer mixture.

Optional additives for poly (meth) acrylimides

Of Furthermore, the mixtures usual additives be added. Suitable amounts are for. 0 to 20, 0 to 10 or 0 to 5 wt .-% based on the monomer mixture.

The usual Additives are different from the monomers mentioned, crosslinkers, Propellants or initiators.

For this include antistatic agents, antioxidants, mold release agents, Lubricants, dyes, flow improvers, fillers, Light stabilizers and organic phosphorus compounds, such as phosphites or phosphonates, pigments, release agents, weathering agents and plasticizer. Other possible additions are Flame retardants. In addition to halogen-containing flame retardants, the sometimes contain antimony oxides, can also phosphorus-containing Connections are used. Phosphorus compounds are because of the lower smoke toxicity in case of fire preferred. Phosphorus compounds include phosphines, Phosphine oxides, phosphonium compounds, phosphonates, phosphites and / or phosphates. These compounds may be organic and / or inorganic Be natural, such as phosphoric monoester, Phosphonic acid monoesters, phosphoric diesters, Phosphonic diester and phosphoric acid triester as well as polyphosphates.

Further blowing agents for poly (meth) acrylimides

In In another embodiment, the polymerizable Monomer mixture additionally contain other propellants. The other blowing agents are different from the inert gases, which are also used in the context of the invention as a propellant become. However, the polymerizable monomer mixture is preferred no or only insignificant amounts added further blowing agents.

When Propellants can z. As the following compounds or mixtures be used: formamide, formic acid, urea, itaconic acid, Citric acid, dicyandiamide, water, monoalkylureas, Dimethylurea, 5,5'-azo-bis-5-ethyl-1,3-dioxane, 2,2'-azo-bis-isobutyric acid butylamide, 2,2'-azo-bis-isobutyric acid N-diethylamide, 2,2 ', 4,4,4', 4'-hexamethyl-2,2'-azopentane, 2,2'-azo-bis-2-methyl-propane, dimethyl carbonate, di-tert-butycarbonate, Acetone cyanohydrate carbonate, oxi-isobutyric acid methyl ester carbonate, N-methyl urethane, N-ethyl urethane, N-tert-butyl urethane, urethane, oxalic acid, Maleic acid, oxi-isobutyric acid, malonic acid, Cyanformamide, dimethylmaleic acid, tetraacetate of methanetetracarboxylate, Oxamide of n-butyl, trimethyl methane tricarboxylate, Triethyl methane tricarboxylate, and monovalent Alcohols of 3-8 carbon atoms such. Propanol-1, propanol-2, Butanol-1, butanol-2, tert-butanol and iso-butanol.

When further, einpolymerisierendes propellant can tert-butyl methacrylate or tert-butyl acrylate. Split as comonomers used these compounds when heating the pre-polymer the blowing agent Isobutene off.

Inert gas as propellant

The blowing agent used is an inert gas. Inert gases in the context of the invention are gases which are also at he increased pressure and elevated temperature do not undergo chemical reactions with the pre-polymer. A series of gases, such as As hydrogen, propane, butane or pentane, which meet this requirement, are from a practical point of view, increased plant engineering effort to ensure the explosion protection, little suitable, but should not be excluded from the scope therefore already. Preference is given to non-combustible gases. Particularly preferred are nitrogen or carbon dioxide.

expansion

at the expansion of the pre-polymer to the foam part in his final shape is a volume increase z. B. to the Factor 5 to 100, preferably by a factor of 8 to 30. Under one slight expansion of the prepolymer, as in some preferred Process variants takes place in an intermediate step, is a Volume increase by the factor greater than zero to 4, preferably from 0.5 to 3 understood.

Molecular weight of the prepolymer

The excellent mechanical properties of inventively produced Foam part result in particular from the comparative high molecular weight of the prepolymer. The comparatively high molecular weight of the prepolymer is by its preparation conditioned by the casting polymerization process. As the pre-polymer due to its cross-linking a virtually infinite molecular weight has, its molecular weight is approximately by the molecular weight of the molecular chains in uncrosslinked State indicated. These are considerably longer as molecular weights of molecular chains that in others Procedure z. B. in the polymerization of molding compositions.

The molecular weight of the prepolymer can be characterized by a molecular weight M _w (weight average) of at least 1,000,000, preferably at least 3,000,000 g / mol, which is obtained on polymerization of the monomer mixture under otherwise identical conditions but without the crosslinker.

The determination of the molecular weight M _w (weight average) can be carried out, for example, by gel permeation chromatography or by the scattered light method (see, for example, US Pat. HF Mark et al., Encyclopedia of Polymer Science and Engineering, 2nd. Edition, Vol. 10, pages 1 ff., J. Wiley, 1989 ).

method

Process step a

Of the Process step (a) comprises the polymerization of a polymerizable Monomer mixture, which consists essentially of non-crosslinking (Meth) acrylate monomers, crosslinkers and an initiator system composed, in Gußpolymerisationsverfahren to a pre-polymer.

The Gußpolymerisationsverfahren is well known in the art and For example, we can proceed as follows

The Polymerization chamber in which the polymerizable liquid is polymerized, is usually a flat chamber. This consists z. B. from two plane-parallel mold plates and a die plates sealing spacers. This can be an elastic cord or be an elastic seal.

In In practice, it has proven to be expedient to polymerize the liquid to be polymerized, d. H. before filling in the polymerization chamber a To produce degree of conversion of the monomers from 5 to 50%. this has the advantage that the viscosity of the mixture rises sharply, whereby a leakage of the mixture from the polymerization vessel better can be avoided and whereby the filling of the mixture is relieved. In addition, not all the heat of polymerization needs be removed in the polymerization vessel, which is an advantage.

The liquid to be polymerized (cf., for example, the polymerization of methyl methacrylate in the chamber process: Vieweg Esser, Kunststoff-Handbuch, Volume 9, pages 43 to 55, Carl Hanser, Munich 1975 ) is in the sealed on three sides, possibly evacuated chamber from the open fourth side filled. The polymerization is usually carried out in such an arrangement of the chambers, which ensures a temperature control or heat dissipation, so can - lying horizontally in racks - chambers, for example in hot air ovens at high air velocity, in autoclaves using water spray or in water-filled tanks under Polymerisationsbedingun be kept. The polymerization is initiated by heating and / or by irradiation. To dissipate the considerable heat of polymerization, especially in the gel area, targeted cooling is necessary. The polymerization temperatures are usually between 15 and 70 ° C at atmospheric pressure. In the autoclave, they are expediently about 90 to 100 ° C. The residence time of the polymerization chamber in the temperature control medium varies according to the manner of the polymerization batch and the implementation between a few hours and several days.

in the Interest in the widest possible implementation (> 97% polymer) can the temperature again towards the end of the polymerization process be increased for a short time, for example to over 100 ° C, about 120 ° C. It is expediently allowed cool slowly, with the polymer plates of the mold plates can be separated and removed.

Pressure and temperature control in process steps (b) and (c)

the One skilled in the art knows that the behavior of real gases through the ideal gas law can be approximated. With the ideal Gas law can be found areas in which suitable combinations of pressure and temperature prevail, among which the pre-polymer either foams or the foaming suppressed becomes. A person skilled in the art can thus know the invention of the foaming process essential by the choice of pressure and temperature control. One another parameter is formed by the residence times.

Process step b

Of the Process step (b) comprises the loading of the prepolymer with an inert gas as blowing agent at a pressure in the range from 2 to 200, preferably from 2 to 50, in particular from 4 to 30, bar. The Loading can take place in a pressure chamber or in an autoclave. During loading, the inert gas diffuses into the Pre-polymer in. To speed up this process takes place the loading of the pre-polymer preferably at elevated Temperature.

Prefers the loading of the pre-polymer with the inert gas occurs at a temperature which is 50 ° C below or above the Softening temperature of the pre-polymer is.

Under the softening temperature, in particular the Vicat softening temperature VET ( ISO 306-B50 ) Understood.

The Softening temperature or VET of crosslinked poly (meth) acrylates is typically in the range of about 120 ° C. The loading thus takes place in the range of 70 to 170 ° C.

The Softening temperature or VET of the crosslinked poly (meth) acrylimides typically is in the range of about 170 ° C. The loading is therefore in the range of 120 to 220 ° C.

The Duration of loading depends on the temperature. As a guide depending on temperature, pressure and thickness or the specific surface of the prepolymer can z. B. 6 to 24 hours. The higher the temperature, the softer is the pre-polymer and the lower is the Loading time. However, the pre-polymer must not too be soft, because otherwise z. B. could stick to the autoclave wall, which hinders the process. A person skilled in the art may be aware of the present Invention in each case favorable for specific pre-polymers Select pressures, temperatures and loading times or experimentel.

Prefers can after loading the pre-polymer with the inert gas Pressure and temperature are lowered, leaving no or only a slight expansion of the pre-polymer occurs and that the Method by raising pressure and temperature again and the final process step c) continued becomes. This has the advantage that the process step (b) and the process step (c) in spatially separated equipment can be made, resulting in a better overall Facility utilization and cost reduction contributes.

Process step c

Of the Process step (c) involves lowering the pressure and expanding of the prepolymer to the foam part at a temperature at the propellant loaded pre-polymerisate is foamable.

The Temperature at which the propellant loaded pre-polymer foamable depends on a number of factors. The consistency and foamability of the pre-polymer depends z. B. from its composition. The lower the degree of crosslinking, the easier the foamability. The higher the temperature, the softer the pre-polymer is and leaves the easier it is foaming. The pressure in turn acts as a counterforce foaming power. In addition, the pressure acts on the Diffusing out of the inert gas and it is the training achieved only a thin foam skin. As a foaming skin is called a near-surface region of the foam part with significantly increased density. The foaming skin will therefore separated as waste. It is therefore desirable foaming skin keep as low as possible. The suitable temperature ranges therefore extend over a wide range of about 50 to 250, preferably 100 to 220 ° C.

One Temperature range at which the propellant loaded pre-polymer crosslinked poly (meth) acrylates is foamable, z. B. roughly indicated at 50 to 180, preferably at 100 to 150 ° C. become.

One Temperature range at which the propellant loaded pre-polymer crosslinked poly (meth) acrylimides is foamable, z. B. roughly indicated at 100 to 250, preferably at 150 to 220 ° C. become.

Prefers the expansion of the pre-polymer is added to the foam part a lower pressure than when loading the pre-polymer but above normal pressure. This can provide better control over the expansion process and an uncontrolled Foaming that leads to irregular foam structures leads, be avoided.

process variant

Prefers For example, the polymerizable monomer mixture may further contain other Propellant included. In this case, after the Loading the plastic molding with the inert gas Pressure and temperature are lowered, leaving no or only a slight expansion of the pre-polymer occurs. Subsequently The final expansion is by raising the temperature effected without raising the pressure, wherein the foaming force at least partially on the additional blowing agent is due. This is advantageous as a Control of the average pore diameter can be made so can.

Process step d

Of the Process step (d) comprises the fixation of the foam part by lowering the temperature. After the expansion of the foamed state fixed. The finished foam can are taken from the equipment and is ready for Refining by separation of foam skins and more Assembly steps or in particular for further processing to core materials for sandwich constructions of all kinds.

foam piece

To Foam parts are the process of the invention made of crosslinked poly (meth) acrylates.

The density of a foam part, z. As a poly (meth) acrylimidschaums, is preferably in the range of 20 kg / m ³ to 320 kg / m ³ , more preferably in the range of 50 to 110 kg / m ³ .

The Thickness of the core layer of an inventive Foam part for industrial applications can after Separation of the foam skins may, for. In the range of 1 up to 200 mm, in particular in the range of 5 to 100 and especially preferably in the range of 10 to 70 mm

uses

The The invention includes the use of the inventively prepared Foam parts as part or part of parts, in particular as core materials for sandwich constructions for Motor vehicles, rolling stock, aircraft, watercraft, Spacecraft, machine parts, aerials, x-ray tables, Speakers, pipes and wings of wind power plants.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• US 4513118 [0015]

Cited non-patent literature

• - H. Rauch-Puntigam, Th. Völker, acrylic and methacrylic compounds, Springer, Heidelberg, 1967 [0034]
• Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 1, pp. 286 et seq., John Wiley & Sons, 1 New York, 1978. [0034]
• - HF Mark et al., Encyclopaedia of Polymer Science and Engineering, 2nd. Edition, Vol. 10, pages 1 et seq., J. Wiley, 1989 [0045]
• - Vieweg Esser, Kunststoff-Handbuch, Volume 9, pages 43 to 55, Carl Hanser, Munich 1975 [0050]
• - ISO 306-B50 [0055]

Claims (12)

Process for producing a foam part crosslinked poly (meth) acrylates characterized by the following steps a. Polymerization of a polymerizable monomer mixture, consisting essentially of non-crosslinking (meth) acrylate monomers, Crosslinkers and an initiator system composed in Gußpolymerisationsverfahren to a pre-polymer, b. Loading the pre-polymer with an inert gas as blowing agent at a pressure in the range from 2 to 200 bar, c. Lowering the pressure and expanding the Pre-polymer to the foam part at a temperature at which the propellant loaded pre-polymer is foamable d. Fixation of the foam part by lowering the temperature Method according to claim 1, characterized in that that it crosslinked in the crosslinked poly (meth) acrylates Polymethyl (meth) acrylates or crosslinked poly (meth) acrylimides is. Method according to claim 1 or 2, characterized that is used as the inert gas, nitrogen or carbon dioxide. Method according to one or more of the claims 1 to 3, characterized in that during the expansion of the pre-polymer to the foam part an increase in volume by a factor of 5 to 100 he follows. Method according to one or more of claims 1 to 4, characterized in that the molecular weight of the prepolymer is characterized by a molecular weight M _w (weight average) of at least 1,000,000 g / mol, the polymerization of the monomer mixture under otherwise identical conditions, however is obtained without the crosslinker. Method according to one or more of the claims 1 to 5, characterized in that the expansion of the pre-polymer to the foam part at a lower pressure than during loading but the pre-polymer is above normal pressure. Method according to one or more of the claims 1 to 6, characterized in that the loading of the pre-polymer with the inert gas at a temperature that is around 50 ° C below or above the softening temperature of the pre-polymer lies. Method according to claim 7, characterized in that that after loading of the pre-polymer with the inert gas Pressure and temperature are lowered, leaving no or only a slight expansion of the pre-polymer occurs and that the Method by raising pressure and temperature again and the final process step c) continued becomes. Method according to one or more of the claims 1 to 8, characterized in that the polymerizable monomer mixture additionally contains further blowing agents. Method according to claims 1 to 7 and 9, characterized that after loading of the plastic molding with the inert gas pressure and temperature are lowered, so no or only a slight expansion of the pre-polymer occurs and then the final expansion the raising of the temperature is effected without raising the pressure. Foamed part of crosslinked poly (meth) acrylates, can be produced according to one or more of claims 1 to 10th Use of a foam part according to claim 11 as part of or part of motor vehicle parts, Rolling stock, aircraft, watercraft, spacecraft, Machine parts, antennas, x-ray tables, loudspeakers, Pipes or wings of wind power plants.