WO2008059184A2

WO2008059184A2 - Use of a polyolefin-based composition for preparing flexible crosslinked foams

Info

Publication number: WO2008059184A2
Application number: PCT/FR2007/052359
Authority: WO
Inventors: Thomas Fine
Original assignee: Arkema France
Priority date: 2006-11-16
Filing date: 2007-11-16
Publication date: 2008-05-22
Also published as: WO2008059184A3; FR2908777A1

Abstract

The present invention relates to the use, in the motor vehicle, transport vehicle and building fields, of a composition for producing a crosslinked foam, said composition comprising (A) a copolymer of ethylene and of an unsaturated monomer bearing at least one epoxide group and optionally alkyl (meth)acrylate or vinyl carboxylate; (B) a copolymer of ethylene and of an alkyl (meth)acrylate or vinyl carboxylate; (C) a cationic-type polymerization initiator; and (D) a pore-forming agent.

Description

USE OF COMPOSITION BASED ON POLYOLEFINS FOR PREPARING RETICULATED SOFT FOAMS.

Field of the invention The present invention relates to the use of polyolefin-based compositions for obtaining flexible reticulated foams and their uses in the field of automobiles, transport vehicles and buildings for their improved mechanical properties.

Technological Background of the Invention

Flexible foams are mainly used for the soundproofing of vehicles. To allow the formation of these foams, it is possible either to add chemical initiators in the formulations and crosslinking by heating, or to crosslink by ionization.

However, the ionization crosslinking only allows the formation of foamed pieces of limited thickness.

In addition, there are industry requirements for the manufacture of these foams. Indeed, in addition to having good mechanical properties, these foams must be able to be formed quickly, without particular thickness constraints.

For example, in the automotive sector, these foams, which are formed inside a heating tunnel, must be formed within a maximum of 30 minutes.

The use of peroxides as a chemical initiator allows the rapid formation of foams, unlike other types of chemical initiators.

In this field, mention may be made of the application FR 2783831 which describes flexible foams obtained from compositions comprising copolymers chosen from the group of ethylene / vinyl acetate copolymers (EVA), ethylene / propylene / diene monomer terpolymers, butyl rubber with copolymer base of polyolefins. This document describes various crosslinking agents for the manufacture of such foams, and in particular peroxides.

US Pat. No. 6,528,550 describes a composition comprising an EVA copolymer, an ethylene / acrylic acid copolymer and a free radical initiator as crosslinking agent. The presence of the copolymer based on acrylic acid makes it possible to increase the thermal stability of the composition, and thus to increase the temperature during the manufacture of foams and thus reduce their manufacturing time.

However, the use of peroxides as a crosslinking agent for the formation of foams induces a release of volatile organic compounds VOC. However, the formation of VOC must be limited in order to meet increasingly stringent environmental standards, particularly in the automotive field.

There is therefore a need to have a new type of flexible foam as an alternative to existing systems, and meeting all the aforementioned constraints.

Summary of the invention.

The object of the present invention is therefore to provide compositions useful for the preparation of flexible foams forming rapidly, without dimensional constraints, having good mechanical properties, while limiting the release of VOC. These flexible foams find their applications in the field of the automobile, transport vehicles, building.

Thus, the invention proposes the use of a composition for obtaining a crosslinked foam, said composition comprising:

(A) a copolymer of ethylene and an unsaturated monomer bearing at least one epoxide group and optionally alkyl (meth) acrylate or vinyl carboxylate;

(B) a copolymer of ethylene and alkyl (meth) acrylate or vinyl carboxylate;

(C) a cationic initiator, and (D) a porogen.

Surprisingly, the use of a cationic type polymerization initiator in the composition according to the invention allows the formation of foams in times compatible with the requirements of the automotive industry.

Preferably, the unsaturated epoxide of the copolymer (A) is glycidyl (meth) acrylate and the alkyl (meth) acrylate of the copolymer (A) is chosen from

methyl (meth) acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate.

Contrary to the teaching of the document WO 2004/108401 which excludes the use of highly polar crosslinking agents with ethylene / glycidyl (meth) acrylate type copolymers, the Applicant observes that an initiator of the type The composition used with the other constituents of the composition perfectly meets the technical problems mentioned above.

Preferably, the (meth) acrylate of the copolymer (B) is chosen from methyl (meth) acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate.

Preferably, the composition further comprises at least one compound (E) of the plasticizer type E 1 or plasticizer E 2.

Preferably, the plasticizer El is chosen from phthalates, adipates, alkyl benzoates, the alkyl chain having a carbon number greater than 6. Preferably, the plasticizer E2 is chosen from aliphatic or naphthenic oils.

According to one embodiment, the content by weight of the compound (B) relative to the total weight of the composition represents at least 10%, preferably in the range from 25% to 75% by weight, or preferably in range from 30 to 60%.

According to one embodiment, the content by weight of the polymerization initiator (C) relative to the total weight of the composition represents from 0.01% to 5%, preferably in the range from 0.1% to 2%. % in weight.

According to one embodiment, the content by weight of the compound (E) relative to the total weight of the composition represents from 0.5% to 15% by weight, preferably in the range from 2% to 10% by weight, preferably in the range of 2 to 6%.

According to one embodiment, the composition further comprises other additives chosen from mineral fillers, reinforcements, flame retardants and dyes.

Preferably, a flexible foam according to the invention is used as sound insulating element, seal and / or automotive door seal.

FIGS.

Figure 1 shows the evolution of mechanical properties of the crosslinked compositions according to the invention as a function of Lotryl ^® rates provided in Table 1.

Figure 2 illustrates the comparison of the times required to reach 90% of the maximum t90% module level for a Lotader ^® -Lotryl ^® 70-30 mixture at different levels of epoxidized soybean oil and at different temperatures, given in Table 2 . DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

The compositions for preparing the flexible foams according to the invention comprise:

(A) a first copolymer of ethylene and an unsaturated monomer (i) bearing at least one epoxide group and (ii) optionally alkyl (meth) acrylate or vinyl carboxylate;

(B) a second copolymer of ethylene and an alkyl (meth) acrylate or vinyl carboxylate;

(C) a cationic type polymerization initiator and; (D) a pore-forming agent.

(i) the unsaturated monomer comprising at least one epoxide group is a monomer unit derived from a compound containing at least one epoxy group and copolymerizable with ethylene.

By way of example of unsaturated epoxides (i), mention may be made of: aliphatic glycidyl esters and ethers, such as glycidyl allyl glycidyl ether, vinyl glycidyl ether, maleate and itaconate, (meth) acrylate, glycidyl and

alicyclic glycidyl esters and ethers such as 2-cyclohexene-1-glycidyl ether, cyclohexene-4,5-diglycidyl carboxylate, cyclohexene-4-glycidyl carboxylate, 5-norbornene-2-methyl-2-glycidyl carboxylate and endo cis-bicyclo (2,2,1) -5-heptene

2,3-diglycidyl dicarboxylate.

The copolymer of ethylene and unsaturated epoxide may also comprise other monomers (ii) comprising an unsaturated ester group and which may be chosen, for example, from: - vinyl esters of saturated carboxylic acids, such as vinyl, vinyl propionate or vinyl butyrate;

saturated carboxylic acid esters such as alkyl (meth) acrylates having up to 24 carbons.

Preferably, the copolymer (A) according to the invention is a copolymer of ethylene and an unsaturated epoxide which can be obtained by copolymerization of ethylene and an unsaturated epoxide or by grafting the unsaturated epoxide on polyethylene. The grafting can be carried out in the solvent phase or on the molten polyethylene in the presence of a peroxide. These grafting techniques are known per se. As for the copolymerization of ethylene and an unsaturated epoxide, it is possible to use the so-called radical polymerization processes which usually operate at pressures between 200 and 2500 bar. By way of example, the unsaturated epoxide can be grafted onto the following polymers:

polyethylene, copolymers of ethylene and of an alphaolefin, polyethylenes such as VLDPE (very low density PE), ULDPE (ultra-low density PE) or metallocene PE; copolymers of ethylene and at least one vinyl ester of saturated carboxylic acid such as vinyl acetate, vinyl propionate or vinyl butyrate.

copolymers of ethylene and of at least one unsaturated carboxylic acid ester, such that the alkyl (meth) acrylates may have up to 24 carbons;

elastomers EPR (ethylene / propylene rubber) or EPDM (ethylene / propylene / diene);

mixtures of polymers chosen from the preceding ones.

The copolymer (A) of the invention is advantageously an ethylene / alkyl (meth) acrylate / unsaturated epoxide copolymer.

Advantageously, it may contain up to 40% by weight of alkyl (meth) acrylate.

The amount of alkyl (meth) acrylate is advantageously from 20 to 35%.

The unsaturated epoxide is advantageously glycidyl (meth) acrylate.

Advantageously, the alkyl (meth) acrylate is chosen from methyl (meth) acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate and 2-ethylhexyl acrylate. .

This copolymer can be obtained by radical polymerization of the monomers.

(B) the second copolymer comprises a copolymer of ethylene and an alkyl (meth) acrylate or vinyl carboxylate. The alkyl (meth) acrylate and vinyl carboxylate may be chosen from those mentioned above in the description of (A).

This second polymer does not comprise monomer units (ii) of the epoxy type.

This compound acts as a non-reactive diluent in the unfoamed composition.

Due to its presence, the mechanical properties of non-foamed crosslinked materials are improved. According to a preferred embodiment, the content by weight of the compound (B) relative to the total weight of the composition represents at least 10%, preferably in the range of 25% to 75% by weight.

(C) the initiator or initiator of cationic type polymerization.

Among the polymerization initiators used in our invention, mention may be made of all initiators of cationic type such as those described in the US application.

2003/0176585 in paragraphs [0041] to [0048]. Preferably, the cationic type polymerization initiators are the BF3 complexes in solid or liquid form, such as the BF3-monoethylamine, BF3-benzylamine, BF3-monoisopropylamine complexes.

For reasons of ease of use in polymer blending operations, the solid forms of BF3 complexes are preferred.

A combination of different polymerization initiators may be considered.

The content by weight of the polymerization initiator (C) relative to the total weight of the composition is from 0.01% to 5%, preferably in the range of 0.1% to 2% by weight. Despite the presence of copolymer B as a non-reactive diluent, cationic polymerization initiators surprisingly proved to be very effective. The use of the formulation according to our invention has allowed the rapid formation of foams having good mechanical properties, while limiting the formation of VOCs. (D) the poroqene agent or blowing agent.

Expansion agents are divided into two main classes: volatile organic agents such as chlorofluorocarbons (CFCs) and chemical agents such as azodicarbonamide. All blowing agents are capable of being used according to the invention, according to all the well-known embodiments of the prior art. However, it is preferred to use alone or in combination non-VOC generating pore-forming agents to prevent their emission, such as, for example, azodicarbonamide such as Genitron® marketed by Lanxess, oxybis benzene sulfonyl hydrazide (OBSH) para-toluene sulfonyl hydrazide or Expancel ^® sold by AkzoNobel. The content by weight of the compound (D) relative to the total weight of the composition represents at most 10%.

(E) The plasticizer or plasticizer compound.

In the compositions according to the invention, a compound (E) of the plasticizer or plasticizer type can be added. As a plasticizer, this compound (El) is chosen from aliphatic or naphthenic oils. As a plasticizer, this compound (E2) is chosen from phthalates (for example di-octyl phthalate), adipates (for example di (2-ethylhexyl) adipate) and alkyl benzoates, the alkyl chain comprising a number of carbon greater than 6. These compounds are used in solid or fluid form.

Preferably, when adding a plasticizer (E2), it can be functionalized and used preferably epoxidized soybean oil (e.g. Ecepox Arkema ^®). These compounds may be used alone or as a mixture and it may especially be used a mixture containing both a plasticizer and a plasticizer.

The content by weight of the compound (E) relative to the total weight of the composition represents from 0.5% to 15% by weight, preferably in the range from 2% to 10% by weight.

The addition of this compound in the unfoamed composition accelerates the crosslinking reaction and thus counterbalance the decrease in the rate of crosslinking due to the presence of the compound (B).

(F) other additives or fillers It would not be outside the scope of the invention to add mineral fillers (talc,

CaCθ3, kaolin ...), reinforcements (glass fibers, mineral fibers, carbon fibers, etc.), flame retardants and dyes.

Process for the preparation of crosslinked flexible foams

1) Step of mixing the ingredients and obtaining a non-crosslinked composition:

Several methods of preparation can be used. The most common is to dry mix all the components: polymers (A) and (B), the blowing agent (D) and the polymerization initiator (C). The mixtures of the compounds are made in an internal mixer (Brabender type). The ingredients are introduced into the preheated mixer at a temperature chosen so as to be just above the melting temperature of the polymers. Once the polymers are melted, optionally the compound (E) is added. Once the mixture has become homogeneous, the cationic polymerization initiator (C) is added. The mixing time is generally 5 to 10 min from the end of addition of the initiator.

Another way to prepare the mixture is to extrude the mixture (A) and (B) to obtain a homogeneous mixture. This mixture is then taken up in the internal mixer as previously described.

Other types of mixer can be used such as single-screw, twin-screw extruders, BUSS co-kneaders.

Another way of preparing the mixture is to premix the polymers and to add, in a second step, the blowing agent and then the initiator.

Another possibility is to make the mixture (A) and (B) entirely extrusion with injection of the compound (E) if it is liquid. Here the technical difficulty is to avoid the initiation of the crosslinking reaction during this transformation step, the self heating in extruder being larger than in kneader. According to another embodiment, rather of industrial type, the compositions can be prepared in internal mixer or extruder and then granulated.

In the case of an addition of liquid plasticizer or fluidizer for example of the epoxidized soybean oil type, it can be added to the dry mix to impregnate the granules if its amount is small. If the quantity is large, the liquid will be injected.

Uncrossed non-foamed blends, for example in the form of granules, can then be shaped by injection or compression at low temperature, to produce a preformed structure or a plate. During this step, it should avoid crosslinking or foaming the room. To do this, it is necessary to perform the transformation at a low temperature, for example between 20 ⁰ C and 100 ⁰ C, and in a short time, for example between 10 and 60 min.

The preformed structure may advantageously then be positioned in the structure of a vehicle before the crosslinking and foaming step, for example by heating when passing through a heating tunnel. If the presence of other additives is expected, these would be introduced during the mixing step (internal mixer or extrusion), just before the initiator which is always introduced last.

2) Crosslinking and moussaqe stage.

The crosslinking step is carried out by any type of crosslinking process according to the type of cationic type polymerization initiator used and according to methods well known in the art.

Preferably, and more particularly the BF3 complexes, the crosslinking is carried out by heating. Heating is usually done in an oven.

The oven is preheated to a temperature ranging from 150 ^° C. to 200 ^° C. and preferably to 175 ° C. This is the average temperature of heated tunnels used in the automotive industry. The residence time in the heating tunnel is estimated at 30 min.

During heating, the expansion of the crosslinked polyolefin foams occurs in all three dimensions, when no particular stress is applied. It is important to carefully adjust the degree of crosslinking of the resin at the beginning of the expansion and throughout its duration; the content of the starting compositions of expansion agent and crosslinking in the case of chemical crosslinking is, of course, adapted for this purpose as well as the times and temperatures of the heat treatments.

In the preparation of crosslinked polyolefin foam, the onset of expansion usually takes place in an already partially crosslinked state of the composition. This measure aims at increasing the viscosity of the composition and thus conditions the regularity and the fineness of the cell structure finally obtained. In this case, the crosslinking continues during the expansion and, optionally, after.

Soft foams.

The foams obtained according to the process described above have a compression, measured according to ASTM D 1667 with a compression ratio of 30.

% and a compression speed of 10 mm / min, at most equal to 7 N / cm ² for a density of at least 100 kg / m ³ , it being understood that this maximum compression is likely to decrease for lower densities and grow for higher densities. Preferably, the gel level of this foam, defined as the weight percentage of the insoluble fraction (in dry extract) of a 50 mg sample immersed for 24 hours at 120 ^° C. in 25 ml of molecular sieve dried xylene, is between 30 and 70%, especially between 40 and 60%.

Use of the compositions according to the invention The compositions according to the invention are used for making flexible foams which are used in the field of the automobile, transport vehicles, the building, in particular as sound insulation, gasket, automobile door seal, etc.

The mechanical properties of the flexible foams obtained from the compositions according to the invention are related to the mechanical and rheological properties of the non-foamed crosslinked compositions. EXAMPLES

The following examples are intended to illustrate the invention without limiting its scope.

In the examples which follow, the components used are as follows: The copolymer (A) is a copolymer of ethylene (67%) - methyl acrylate

(25%) - glycidyl methacrylate (8%) manufactured by Arkema under the reference Lotader® GMA AX8900 whose flow index or MFI (or MeIt Flow Index) is 6g / 10min measured according to ASTM standard Dl 238 and the point melting point is 60 ^° C. measured by differential scanning calorimetry. The copolymer (B) is a copolymer of ethylene (62%) -methyl acrylate (28%) manufactured by Arkema under the reference Lotryl® 28MA07, whose MFI is 6-8 g / 10 min measured according to ASTM standard Dl 238 and the melting point is 65 ° C measured by differential scanning calorimetry.

Compound (C) is a BF3-monoethylamine complex. The compound (D) pore-forming agent is the Genitron® EPC from Lanxess. The compound (E) is epoxidized soybean oil under the reference Ecepox® PB3 (oxirane number equal to 6.5-7.5 g C / I OOg). EXAMPLE 1 Preparation of the Crosslinked Compositions According to the Invention

1) Mixing step of the ingredients: The mixtures are made in an internal mixer (Brabender type). The Lotader® and Lotryl® polymers are introduced into the preheated mixer between 90 ^° C. and 110 ^° C. This temperature is chosen so as to be just above the melting point of the two polymers. Once the polymers are melted, Ecepox® Epoxidized Soybean Oil and Genitron® Blowing Agent are added. Once the mixture has become homogeneous, the BF3 monoethylamine complex initiator is added. The mixing time is 5 min from the end of the addition of the initiator.

The blowing agent could also be introduced before or after the plasticizer. 2) Crosslinking and moussaqe step: The crosslinking step is done in an oven. The oven is preheated to 175 ° C. The compositions leaving the internal mixer are previously compressed at 90 ^° C. or 110 ^° C. so as to obtain a plate. Samples are then cut and placed in the oven for 30min. It is during this step that the system reticules.

It is observed that there is no inhibition of the effects of the pore-forming agent by the introduction of the polymerization initiator. In other words, the introduction of this initiator does not hinder the formation of the foam.

EXAMPLE 2 Properties of the products obtained:

Mechanical properties. Experimental technique:

The values of modulus, tensile stress and elongation at break were determined on IFC type tensile specimens of thickness 1 .2 mm. The experiments are performed on an extensometer at 50mm / min.

To characterize the crosslinking kinetics, shear modulus monitoring experiments G '(conservation modulus) and G "(loss modulus) were carried out at different isotherms (150 ^° C., 160 ^° C., 170 ^° C. and 180 ^° C. ⁰ C). the determination of the time required to reach 90% of the level of maximum modulus at a given temperature is a AER type rheometer, the stress frequency was set at 10 rad / s and strain at 5%. Mechanical properties such as modulus, stress and elongation at break of crosslinked compositions containing different concentrations of polymer (A) (Lotαder ^®) and polymer (B) (Lotr are shown in Table 1 below:

Figure 1 gives the graphical representation of the results in Table 1.

As shown in Figure 1, the crosslinked system based on 100% of Lotader ^® AX8900 has a stress and an elongation at very low rupture.

By comparison, if we refer to a peroxide crosslinked ethylene-vinyl acetate system, the elongation at break is of the order of 650% and the breaking stress of 20 MPa for a Young's modulus equal at 15 MPa.

To approach the results of a reference system, the Lotader ^® / cationic initiator system was modified by adding Lotryl ^® . Figure 1 clearly shows that from 30% of Lotryl in the system, the module rises above 10 MPa and the elongation at break is doubled compared to the system without Lotryl ^® . From 50% Lotryl ^®, the elongation at break becomes higher than 250%, which is quite acceptable for non-flexible foam material having a modulus of around 10MPa.

Thus, the mechanical properties of non-foamed flexible materials can be transposed to soft foamed materials.

The values of the time required to reach 90% of maximum modulus level for the compositions Lotader ^® ^® -Lotryl epoxidized soybean -Oil and initiator at a given temperature, are shown in Table 2 below:

Figure 2 gives a graphical representation of the results of Table 2. As shown in Figure 2, the addition of 30% Lotryl ^® in a Lotader ^® and initiator system induces a decrease in the crosslinking kinetics. For example, 160 ⁰ C, without Lotryl ^® must 891 seconds to reach 90% of the maximum modulus level whereas with Lotryl ^® should be 1143 seconds.

As shown in Figure 2, the addition of Ecepox ^® up to 5% accelerates the kinetics of the system containing 70% Lotader ^® AX8900 and 30%

Lotryl ^® 28MA07, whatever the test temperature.

We also note that there is an optimum rate of Ecepox ^® between 5% and 10% which accelerates the kinetics of crosslinking of the system.

Table 3 shows the mechanical properties such as modulus, stress and elongation at break of cured compositions containing different epoxidized soybean oil concentrations (Ecepox ^® PB3). The mechanical properties are not disturbed by the introduction of plasticizer.

Claims

1. Use of a composition for obtaining a crosslinked foam, said composition comprising: (A) a copolymer of ethylene and an unsaturated monomer bearing at least one epoxide group and optionally (meth) acrylate alkyl or vinyl carboxylate; (B) a copolymer of ethylene and alkyl (meth) acrylate or vinyl carboxylate; (C) a cationic polymerization initiator;

(D) a pore-forming agent.

2. Use according to claim 1 wherein the cationic initiator is a complex of BF3 in solid or liquid form, selected from the complexes BF3-monoethylamine, BF3-benzylamine, BF3-monoisopropylamine.

3. Use according to claim 1 or 2 wherein the unsaturated epoxide of the copolymer (A) is glycidyl (meth) acrylate and the alkyl (meth) acrylate of the copolymer (A) is selected from (meth) acrylate methyl, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate.

4. Use according to one of claims 1 to 3 wherein the alkyl (meth) acrylate of the copolymer (B) is selected from methyl (meth) acrylate, ethyl acrylate, acrylate and the like. -butyl, isobutyl acrylate, 2-ethylhexyl acrylate.

5. Use according to one of claims 1 to 4 further comprising at least one compound (E) of the plasticizer type El or fluidifying E2, the fluidifier E2 is preferably functionalized.

6. Use according to claim 5 wherein the plasticizer El is selected from aliphatic or naphthenic oils.

7. Use according to one of claims 1 to 7 wherein the content by weight of the compound (B) relative to the total weight of the composition is at least 10%, preferably in the range of 25% to 75% by weight, or preferably in the range of 30 to 60%.

8. Use according to one of claims 1 to 8 wherein the content by weight of the polymerization initiator (C) relative to the total weight of the composition is from 0.01% to 5%, preferably in the range ranging from 0.1% to 2% by weight.

9. Use according to one of claims 5 to 9 wherein the content by weight of the compound (E) relative to the total weight of the composition is from 0.5% to 15%, preferably in the range of 2% to 10%, and preferably in the range of 2 to 6%.

10. Use according to one of claims 1 to 10 further comprising other additives selected from mineral fillers, reinforcements, flame retardants and dyes.

1 1. Use according to one of claims 1 to 10 wherein the blowing agent (D) does not emit VOC.

12. Use of a flexible foam obtained from a composition for obtaining a reticulated foam, said composition comprising:

(B) a copolymer of ethylene and alkyl (meth) acrylate or vinyl carboxylate;

(C) a cationic polymerization initiator;

(D) a pore-forming agent. in the field of the automobile, transport vehicles, the building.

13. Use according to claim 12 wherein the cationic initiator is a complex of BF3 in solid or liquid form selected from the complexes BF3-monoethylamine, BF3-benzylamine, BF3-monoisopropylamine.

14. Use according to claim 12 or 13 as a sound insulating element, gasket, and / or automotive door seal.