EA022941B1 - Process to increase the melt flow index of an expandable vinyl aromatic polymer - Google Patents

Abstract

The present invention is a process to increase the melt flow index of an expandable vinyl aromatic polymer while maintaining the same or a higher 10% compression resistance, comprising the steps of: a) providing a vinyl aromatic polymer in the molten state, b) introducing 1-10% by weight calculated with respect to the polymer (a) of an expanding agent englobed in the polymeric matrix, c) introducing 0.1 to 5% by weight calculated with respect to the polymer (a) of PiB (polyisobutene), homogeneously distributed in the polymeric matrix, wherein the proportion of PiB is adjusted to increase the Melt Flow Index (MFI) measured at 200°C under a 5 kg load, in accordance with DIN ISO 1133, from an initial index to a final index such as the 10% compression strength measured in accordance with EN826, of the foam made with said expandable vinyl aromatic polymer of the final index is essentially the same or higher than the foam made with said expandable vinyl aromatic polymer of the initial index.

Description

The invention relates to expandable vinyl aromatic polymers with increased thermal insulation ability and containing polyisobutene (ΡίΒ), in particular to a method for increasing the melt flow index of a expandable vinyl aromatic polymer.

Foaming vinyl aromatic polymers and among them, in particular, expandable polystyrene, are known products that have been used for a long time for the manufacture of foamed products that can be embedded in various application areas, among which one of the most important is the field of thermal insulation. These foamed products are obtained by expanding the granules of the expandable polymer, impregnated with gas, and molding expanded particles contained within the closed form, by simultaneously applying pressure and temperature. Particle expansion is typically carried out using water vapor or another gas maintained at a temperature slightly above the glass transition temperature (TD) of the polymer.

A particular application for foamed polystyrene is its use for thermal insulation in the construction industry, where it is usually used in the form of flat sheets. Polystyrene foam sheets are typically used with a density of approximately 15-30 g / l.

BACKGROUND OF THE INVENTION

The term expandable granules based on vinyl aromatic polymers as used in the present description and claims refers to vinyl aromatic polymers in the form of grains containing an expandable system and other additives.

These expandable thermoplastic polymers in the form of grains, in particular, are used after foaming and molding, in the manufacture of household appliances or other industrial equipment, in packaging and thermal insulation in construction in connection with their thermal insulation properties. Thermoplastic vinyl aromatic polymers, such as polystyrene, can be made foamable after incorporating a foamable agent into the polymer matrix. Typical foaming agents for vinyl aromatic polymers contain at least one liquid hydrocarbon containing from 3 to 7 carbon atoms, a halogenated hydrocarbon, carbon dioxide or water. The amount of blowing agent is usually from 2 to 15 wt.%. Foaming polymers are usually obtained in the form of granules or grains, which, under the influence of heat supplied, for example, from steam, are first foamed to achieve the desired density, and after a certain exposure time, they are sintered in closed molds to obtain blocks or the desired final product.

The preparation of such expandable granules has already been described in patent documents EP 126459, FROM 2006211780, FROM 2005156344, FROM 6783710 and AO 2008141766.

Obtaining granules of RE (polystyrene) with the inclusion of pentane is difficult due to the need to maintain a balance between the ease of extrusion / granulation and the foaming process and the compressive strength of blocks obtained from sintered foam granules (insulating boards, etc.).

When performing granulation to obtain granules, the fluidity of polymer blends containing fillers is critical, especially if it is necessary to obtain micro granules. The usual way to modify rheology and reduce viscosity is to reduce molecular weight. This method has limitations due to the absence of linkages between molecules at low molecular weight chains. An alternative is to add oil, however, when using an oil-containing material in the area associated with the use of foams, the compressive strength decreases. In the present invention, polyisobutylene (also called polyisobutene or ΡίΒ) is used instead of oil. ΡίΒ allows to reduce the viscosity of the polymer while maintaining the same or obtaining a higher compressive strength at 10% linear strain. As an example, ΜΡΙ (melt flow index) (see the measurement standard in the examples) is increased by 0.5-2.5 units. As a result, a higher molecular weight can advantageously be used.

EP 770 632-1 discloses a high-strength monovinyl aromatic polymer compound comprising an impact-resistant rubber-modified monovinyl aromatic polymer with improved environmental cracking resistance, the above polymeric compound being formed by polymerizing a monovinyl aromatic compound in the presence of rubber and an additive consisting essentially of a polyethylene polymer consisting mainly of weight low / medium to high, according to measured viscosity from pr about 48 to about 4380 centistokes (cSt) at 99 ° C. This document also describes a high-strength monovinyl aromatic polymer compound, consisting mainly of an impact-resistant rubber modified polymer with improved resistance to cracking under the influence of the environment, the above polymer being formed by polymerization of the monovinyl aromatic compound in the presence of rubber and a mixture of approximately equal parts of two additives comprising mineral oil and polyisobutylene. The specified prototype does not apply to expandable monovinyl aromatic polymers.

Patent document IE 2019945 describes expanded polystyrene obtained by extrusion. A mixture of polystyrene, diisodecanyl phthalate, ΡίΒ, pentane and citric acid is mixed in an extruder and foamed. The specified prototype does not apply to expandable monovinylaromatic polymer.

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Patent document I8 3929686 describes a composition and method for producing expandable styrene polymers, where low molecular weight isobutylene polymers are used in an amount of from about 0.02 to about 0.15 wt.%, Based on the styrene polymer, as a nucleating agent for producing foamed styrene a polymer having a very small average cell size. In this document there is no mention of the obtained insulation boards and their compressive strength.

SUMMARY OF THE INVENTION

The invention relates to a method for increasing the melt flow index of a foamable vinyl aromatic polymer while maintaining the same or obtaining higher compressive strength at 10% linear deformation.

In one embodiment, the present invention relates to a method for increasing the melt flow index of a foamable vinyl aromatic polymer while maintaining the same or obtaining higher compressive strength at 10% linear strain, comprising the steps of:

a) provide a vinyl aromatic polymer in a molten state;

b) injecting 1-10 wt.% based on the polymer (a) of the blowing agent into the polymer matrix;

c) from 0.1 to 5 wt.% are introduced and uniformly distributed in the porlimeric matrix based on (a) ΡίΒ (polyisobutene) polymer, where the relative content ΡίΒ is adjusted to increase the melt flow index (ΜΡΙ) measured at 200 ° C and a weight of 5 kg, in accordance with the standard ΌΙΝ Ι 8Θ 1133, from the initial index to the final index so that the compressive strength at 10% linear deformation of the foam obtained using the above expanded onto vinylaromatic polymer with a final index was the same or higher than m of foam obtained using the above expandable vinylaromatic polymer with an initial index.

A method for increasing the melt flow index of a foamable vinyl aromatic polymer may further include introducing and uniformly distributing in the polymer matrix up to 20% by weight, based on polymer (a), one or more fillers other than ΡίΒ.

DETAILED DESCRIPTION OF THE INVENTION

Regarding the vinyl aromatic polymer used, mention may be made of polystyrene, an elastomer-modified polystyrene;

copolymers of styrene and acrylonitrile (8ΑΝ), modified with an 8 эласт elastomer, in particular ΑΒ8, which is obtained, for example, by grafting (graft polymerization) of styrene and acrylonitrile onto the backbone of a polybutadiene or butadiene-acrylonitrile copolymer;

mixtures of 8ΑΝ and ΑΒ8;

copolymers with styrene blocks and blocks of butadiene or isoprene, or a mixture of butadiene / isoprene, these block copolymers can be linear block copolymers or star-shaped block copolymers, they can be hydrogenated and / or functionalized; such copolymers are described in υΕΕΜΑΝΝ'8 ΕΝΟΥΟΕΟΡΕΌΙΑ ΘΡ ΙΝΏυ8ΤΚΙΑΕ ΟΗΕΜΙ8ΤΚΥ, JS ebyui (1995) Yo1 Α26, Radek 655-659; То1а1 Ρеί ^ ссеть са1δ sells them under the trademark Р1пас1еаг®, ΒΑ8Ρ - under the trademark 81уго1и. \ ®. Сеутоп ΡΙιίΠίρκ Сёшюа1 - under the trademark К-Кекш®;

8ΒΚ (styrene-butadiene rubber).

Possible examples of the above elastomers are ΕΡΚ (abbreviation for ethylene-propylene rubber or ethylene-propylene elastomer), ΕΡΌΜ (abbreviation for ethylene-propylene-diene rubber or ethylene-propylene-diene elastomer), polybutadiene, acrylonitrile butene copolymer copolymer, acrylonitrile butadiene copolymer copolymer blocks and blocks of butadiene, or isoprene, or a mixture of butadiene / isoprene. These block copolymers can be linear block copolymers or star-shaped block copolymers, they can be hydrogenated and / or functionalized (see above).

In the vinylaromatic polymer just mentioned, part of the styrene can be replaced by unsaturated monomers copolymerizable with styrene, for example alpha-methylstyrene or (meth) acrylates. Other examples of styrene copolymers that can be mentioned include chloro polystyrene, poly-alpha-methyl styrene, styrene-chloro-styrene copolymers, styrene-propylene copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-vinyl acetate copolymers, styrene-vinyl acetate copolymers, styrene-vinyl acetate copolymers, styrene-vinyl chloride copolymers, styrene-vinyl chloride copolymers copolymers (methyl, ethyl, butyl, octyl, phenyl acrylate), styrene alkyl methacrylate copolymers (methyl, ethyl, butyl, phenyl methacrylate), styrene methyl chloro acrylate copolymers and styrene acrylonitrile acrylac Rilate copolymers.

In a specific embodiment, the vinyl aromatic polymer used includes:

ί) from 60 to 100 wt.% of one or more C _8- 1 ₂ vinyl aromatic monomers; and ίί) from 0 to 40% by weight of one or more monomers selected from the group consisting of C _1-4 alkyl esters of acrylic or methacrylic acid, and acrylonitrile, and methacrylonitrile; the polymer of which can be grafted or included in an amount of from 0 to 20 wt.% from one or more rubber polymers.

Rubber polymers can be selected, for example, from the group including:

a) copolymers and homopolymers of C _4-6 conjugated diolefins;

b) copolymers comprising from 60 to 85% by weight of one or more C _4-6 conjugated diolefins and from 15 to 40% by weight of a monomer selected from the group consisting of acrylonitrile and methacrylonitrile, and

c) copolymers comprising from 20 to 60, preferably from 40 to 50 wt.% of one or more C _8-12 vinyl aromatic monomers that are unsubstituted or substituted by a C _1-4 alkyl radical, and from 60 to 40, preferably from 60 to 50% by weight of one or more monomers selected from the group consisting of C4-6 conjugated diolefins.

Rubber can be obtained in several ways, preferably by polymerization in emulsion or in solution. These methods are well known to those skilled in the art. Vinyl aromatic polymers can be obtained in several ways. This method is well known to specialists in this field.

If present, the rubber is preferably present in an amount of from about 3 to 10% by weight. Polybutadiene is a particularly suitable rubber.

In a specific embodiment, in which the vinyl aromatic polymer used is polystyrene, it may be crystalline polystyrene or rubber modified polystyrene. Rubber modified polystyrene is called ΗΙΡ8 (high strength polystyrene). The method of obtaining ΗΙΡ8 is well known to specialists in this field. The rubber is dissolved in the styrene monomer (in fact, the rubber increases unlimitedly in size under the action of the monomer). This results in two continuous phases. The resulting solution is fed into the reactor and polymerized usually by shear. When the degree of polymerization is approximately equal to the weight% of rubber in the system, it is reversed (for example, the styrene / styrene phase of the polymer becomes continuous and the rubber phase becomes discrete). After phase reversal, the polymer is isolated in a manner that is substantially similar to that of polystyrene. The polymer is prepared using conventional polymerization methods in volume, solution or suspension.

The vinyl aromatic polymers used in the present invention may be copolymers or homopolymers of C _8-12 vinyl aromatic monomers. Some vinyl aromatic monomers may be selected from the group consisting of styrene, alpha-methylstyrene and parameter methylstyrene. Preferably, the vinyl aromatic monomer is styrene. The vinyl aromatic polymer may be a copolymer comprising 60 to 100 wt.% Of one or more C _8-12 vinyl aromatic monomers and 0 to 40 wt.% Of one or more monomers selected from the group consisting of C1-4 alkyl acrylic or methacrylic esters acids and acrylonitrile and methacrylonitrile. Suitable esters of acrylic and methacrylic acids include methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate and butyl methacrylate. The vinyl aromatic polymers described in the present invention may be rubber modified.

The predominantly used vinyl aromatic polymer is a monovinyl aromatic polymer.

In an embodiment, the vinyl aromatic polymer used may be a branched aromatic monomer. As for the branched aromatic monomer, it is described in patent document UO 2006081295, the contents of which are included in the present application. A branched aromatic ionomer includes a copolymerization product of a first monomer that includes an aromatic moiety and an unsaturated alkyl moiety, and a second monomer that includes an ionic moiety and at least two unsaturated moieties, where the ionic moiety has at least two ionizable groups, a cationic group that ionizes with the formation of cations, and an anionic group that ionizes with the formation of anions, and where the cationic group is polyvalent and is able to form bridged link with other molecules.

Advantageously, the first monomer is selected from the group consisting of styrene, alpha-methylstyrene, 1-butylstyrene, p-methylstyrene, vinyltoluene and mixtures thereof. Preferably, the first monomer is styrene.

Components that can be used as the second monomer include, but are not limited to, zinc diacrylate, zinc dimethacrylate, zinc divinyl acetate, zinc diethyl fumarate and the like; copper diacrylate, copper dimethacrylate, copper divinyl acetate, copper diethyl fumarate and the like; aluminum triacrylate, aluminum trimethacrylate, aluminum trivinyl acetate, aluminum triethyl fumarate and the like; zirconium tetraacrylate, zirconium tetramethacrylate, zirconium tetravinyl acetate, zirconium tetraethyl fumarate and the like. For components that have monovalent cationic groups, the second monomer may be sodium acrylate, sodium methacrylate, silver methacrylate and the like. These components and any component suitable as the second monomer can be obtained, for example, by reaction of an organic acid or anhydride with a metal or metal salt.

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Preferably, the second monomer is selected from the group consisting of zinc diacrylate, zinc dimethacrylate, zinc divinyl acetate, zinc diethyl fumarate and the like; copper diacrylate, copper dimethacrylate, copper divinyl acetate, copper diethyl fumarate and the like; aluminum triacrylate, aluminum trimethacrylate, aluminum trivinyl acetate, aluminum triethyl fumarate and the like; zirconium tetraacrylate, zirconium tetramethacrylate, zirconium tetravinyl acetate and mixtures thereof. Preferably, the second ionomer is zinc diacrylate or zinc dimethacrylate.

The first monomer may be a mixture of various aromatic monomers, which include an aromatic fragment and an unsaturated alkyl fragment, and / or it can be used alone or in a mixture of up to 50 wt.% With other copolymerizable monomers. Examples of these monomers are (meth) acrylic acid, C ^ Cd alkyl esters of methacrylic acid such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, isopropyl acrylate, butyl acrylate, amides and nitriles of (meth) acrylic acid such as acrylamide, methacrylamide, methacrylonitrile, butadiene, ethylene, divinylbenzene, maleic anhydride, etc. Preferred copolymerizable monomers are acrylonitrile and methyl methacrylate.

The monomers used to produce branched aromatic ionomers can interact in various ways, affecting the physical properties of the ionomers. The first way is the formation of covalent bonds as a result of polymerization of unsaturated fragments. The second way that the monomers used to produce branched aromatic ionomers can interact is to form a bridge in which the polyvalent cationic group forms a coordination bond with two anionic groups that are integrated into the backbones of at least two separate chains. Such coordination can, in essence, lead to cross-linking of the two chains, thus increasing the total effective molecular weight of this segment to the sum of the two chains. The third way in which monomers used to produce branched aromatic ionomers can interact is to form several bridges, as has just been described. The more crosslinking occurs between the chains, the less flexible the three-dimensional structure of the ionomer becomes, which can result in lower melt flow rates and increased melt strength. In yet another, fourth way of interaction, when the cationic groups are monovalent, ionic fragments, not being completely connected by bridges, can still be connected due to the forces of hydrophobic-hydrophilic interaction.

In these embodiments, this weaker but still measurable force can come from the relatively non-polar hydrophobic, non-ionic parts of the molecule, which are mutually attracted and repelled from the polar hydrophilic ionic parts of the ionomer. These forces become more noticeable as the relative concentration of the second monomer increases. The listed four ways are not all possible variants of the interaction of monomers. In addition, most of the properties of ionomers that are associated with its primary, secondary, and even tertiary structure, such as the glass transition temperatures of ionomers Td, can be affected.

Both the amount of the second monomer and the type of reaction with the first monomer will determine the amount of the second monomer used. Therefore, in some embodiments, when the interaction is weak, for example, if the cationic group of the second monomer is monovalent and a significant effect of the second monomer is required, then branched ionomers are obtained using a relatively large amount of the second monomer, usually with a ratio of the first monomer to the second monomer from about 999: 1 to about 40:60. In other such embodiments, the ratio is from about 95: 5 to about 50:50. In other such embodiments, the ratio is from about 90:10 to about 60:40. Other embodiments are characterized by a ratio of 80:20 to 70:30. In the case of a very strong interaction, for example, when the cationic group is divalent or trivalent, or when it is desired that the second ionomer provide only small changes in the properties of the ionomer, the amount of the second monomer is quite small, varying from about 10 ppm (ppm) to approximately 10,000 rt. In other such ionomers, the range is from about 100 ppm to about 1000 ppm. In other such ionomers, the range is from about 250 ppm to about 800 ppm.

Branched aromatic ionomer is obtained by copolymerization of the first and second monomers. Each of these monomers has at least one polymerizable unsaturated bond. The polymerization can be carried out by any method known to those of ordinary skill in the art of such polymerizations. For example, polymerization can be performed using a polymerization initiator. Examples of polymerization initiators are, for example, radical polymerization initiators such as benzoyl peroxide, lauroyl peroxide, tert-butylperoxybenzoate and 1,1-di-tert-butylperoxy-2,4-di-tert-butylcyclohexane. The amount of polymerization initiator is from about 0 to about 1% by weight of the monomers. In one embodiment, the amount of polymerization initiator is from about 0.01 to about 0.5% by weight of the monomers. In another embodiment, the amount of polymerization initiator is from about 0.025 to about 0.05% by weight of the monomers.

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Alternatively, instead of using an initiator, an ionomer can be obtained by using heat as an initiator. The ionomer can be obtained using an unconventional initiator, such as a metallocene catalyst, as disclosed in US patent No. 6706827, Luy et al., Which is fully incorporated herein by reference. In one embodiment, the monomers can be mixed with a solvent and then polymerized. In another embodiment, one of the monomers is dissolved in another and then polymerized. In yet another embodiment, the monomers can be simultaneously and separately fed to the reactor, either in pure form or dissolved in a solvent, for example, in mineral oil.

In yet another embodiment, the second monomer can be prepared ίη δίίπ either immediately prior to polymerization by admixing feed components, such as unsaturated acid or metal anhydride and alkoxide, in-line or in a reactor. Any method of polymerizing monomers with polymerizable unsaturated bonds known to those skilled in the art of producing such polymers can be used. For example, you can apply the method described in US patent No. 5540813, 8o§a et al., Which is fully incorporated herein by reference. You can apply the methods described in US patent No. 3660535, Rshey et al., And US patent No. 3658946, Vgop51sg1 et al., Both of which are fully included in this document. To obtain branched aromatic ionomers, any general-purpose polystyrene production method can be used.

The branched aromatic ionomer can be mixed with up to 50 wt.% ΟΡΡδ.

Ionomers can be mixed with additives before use for their intended purpose. For example, ionomers can be mixed with flame retardants, antioxidants, lubricants, UV stabilizers, antistatic agents, etc. With branched ionomers, any additive that is known to those of ordinary skill in the art of producing ionomers can be used.

With regard to the preferred vinyl aromatic polymer used, mention may be made of polystyrene, such as, for example, crystalline polystyrene and ΗίΡδ. Polystyrene should preferably have an M \ y (molecular weight) of 130,000 to 210,000 and ΜΡΙ (measured at 200 ° C and a weight of 5 kg, in accordance with the ΌΙΝ ΙδΟ 1,133 standard) in the range of 4 to 20.

As for the blowing agent used, it is selected from aliphatic or cycloaliphatic hydrocarbons containing from 3 to 6 carbon atoms, such as n-pentane, isopentane, cyclopentane or mixtures thereof, halogen-substituted derivatives of aliphatic hydrocarbons containing from 1 to 3 carbon atoms, such as for example, dichlorodifluoromethane, 1,2,2-trifluoroethane, 1,1,2 trifluoroethane; carbon dioxide and water. For pentane, a mixture of npentane and isopentane is preferably used. The relative content of pentane should preferably be in the range from 4 to 7 weight. %

As for ΡίΒ used, the isobutylene polymers of the present invention are preferably isobutylene homopolymers, but also include C ₂ -C ₅ lower C ₂ -C ₅ olefinic hydrocarbons that contain at least about 85% isobutylene monomer units and typically include minor amounts of n-butylene monomer units and relatively small amounts of other lower olefins. The isobutylene polymers used in the present invention are polymers with a molecular weight (number average) of from about 500 to 5000, although it is preferable that their molecular weight be in the range of from about 900 to 3000. The polymers are characterized as hydrophobic molecules with long chains with metal groups on side chains. The relative content of ΡίΒ can be easily adjusted by checking ΜΡΙ of the expandable vinyl aromatic polymer. Apparently, an increase of approximately 1 or 2 g / 10 min is sufficient to easily obtain granules or grains. Preferably, the relative contents (wt.% With respect to polymer (a)) ΡίΒ are from 0.5 to 2.5, preferably from 0.8 to 2.2, more preferably from 1 to 2.

Isobutylene polymers used in the present invention can be obtained by known procedures, and suitable products are commercially available. In a typical process for preparing the subject isobutylene polymers, a hydrocarbon feed, consisting mainly of isobutylene monomer, is contacted with a Friedel-Crafts catalyst at a temperature in excess of about −45 ° C., whereby a suitable low molecular weight polymer is obtained. See, for example, disclosure of US patent No. 2957930. Polymers at the top of the molecular weight range indicated above can be obtained by further contacting the aforementioned low molecular weight polyisobutylene with from about 1 to 10% Friedel-Crafts catalyst for periods of from about 15 minutes to 2 hours and at a temperature of from about 10 to 200 ° P, see, for example, US Pat. No. 3,375,295. Other suitable methods for the preparation of low molecular weight isobutylene polymers are described in US Pat. Nos. 3,501,551, 3,073,876, 3,242,158 and 335,661.

Regarding the fillers used, any material capable of lowering the thermal conductivity and / or improving the properties of the foamed vinyl aromatic polymer can be mentioned. Can

- 5 022941 mention talc, graphite, mica, silicon dioxide, titanium dioxide and barium sulfate.

As for talc, in the embodiment, mention may be made of species that have an average diameter of more than about 8 μm, wherein the indicated average diameter is measured with a Machegm / eg particle size laser analyzer in accordance with the ΙδΟ 13320-1 standard, mention may be made of 20Μ00δ, which is supplied by the company Κίο Τίηΐο Mshegak (Ta1s ye b / ep). Advantageously, talc has an average diameter of more than about 8 microns and less than 100 microns, more preferably in the range of 8-50 microns, preferably in the range of 8-30 microns, more preferably in the range of 9-12 microns. Preferably, 0 (95) is about 100 microns or less, more preferably about 50 microns, even more preferably about 40 microns, preferably about 30 microns. 0 (95) means that 95% of the particles are smaller than this value. Mostly BET is in the range of 0.5-5 m ² / g and preferably in the range of 3-4 m ² / g. The relative content of talc is preferably from 0.1 to 2 wt.% And preferably about 1%.

Mention may also be made of flame retardants, nucleating agents, plasticizers and agents that facilitate the removal of molded and foamed articles from the mold. In particular, it may comprise at least one flame retardant selected in particular from halogenated hydrocarbons, preferably brominated hydrocarbons, in particular, Ο ₆ -Οι ₂ hydrocarbons such as geksabromtsiklogeksan, pentabrommonohlorotsiklogeksan or hexabromocyclododecane, in an amount which can vary from 0.05 to 2 parts by weight, preferably from 0.1 to 1.5 parts by weight per 100 parts by weight of styrene polymer. The composition may further include at least one nucleating agent selected, in particular, from varieties of synthetic wax, in particular varieties of Fischer-Tropsch wax and varieties of polyolefin wax, such as varieties of polyethylene wax or varieties of polypropylene wax, in an amount that can vary from 0 05 to 1 parts by weight, preferably from 0.1 to 0.5 parts by weight per 100 parts by weight of vinyl aromatic polymer. The composition may also include at least one plasticizer selected, in particular, from mineral oils and varieties of petroleum wax, such as varieties of paraffin wax, in an amount that can vary from 0.1 to 1, preferably from 0.1 to 0, 8 parts by weight per 100 parts by weight of vinyl aromatic polymer. The composition may further include at least one agent that facilitates the removal of molded and foamed products from a mold, selected in particular from inorganic salts and stearic acid esters, such as, for example, glycerol mono-, di- or tristearates, and zinc stearate, stearate calcium or magnesium stearate, in an amount that can vary from 0.05 to 1 parts by weight, preferably from 0.1 to 0.6 parts by weight per 100 parts by weight of vinyl aromatic polymer.

Regarding the mechanical properties of the foam, an important parameter is the compressive strength at 10% linear deformation depending on the density of the foam. An advantage of the compositions of the present invention is that they have high compressive strength at 10% linear strain.

The relative content ΡίΒ is adjusted to increase the melt flow index (ΜΡΙ) from the initial index to the final index so that the compressive strength at 10% linear deformation for the foam obtained using the specified expandable vinyl aromatic polymer with a final index is essentially the same or higher than that of a foam obtained from the specified expandable vinylaromatic polymer with an initial index. Essentially the same means that the difference is less than 5%, mainly less than 4%, more preferably less than 3% and preferably less than 2%.

Advantageously, for polystyrene, the compressive strength at 10% linear strain (or stress at 10% strain), which is expressed in kPa, is at least [7.14 x the density of the foam in kg / m ³ - 28]. Which means approximately 50 kPa for a density of 11 kg / m ³ and approximately 150 kPa for a density of 25 kg / m ³ .

As for the method for producing said expandable polymer, it is carried out by mixing the vinyl aromatic polymer in the molten state with a blowing agent or means, ΡίΒ, talc, if necessary, with carbon black, if necessary, with fillers.

In an advantageous embodiment, the mixing is carried out in a chamber equipped with at least one mechanism for mixing, and under conditions of temperature and pressure that can prevent foaming of the composition, preferably in an extruder, in particular in a single screw or twin screw extruder, or in one or more static mixers at a temperature exceeding the glass transition temperature of the polymer, in particular at a temperature in the range from 120 to 250 ° C and at an absolute pressure in the range from 0.1 to 10 MPa.

The preparation of such expandable granules has already been described in patent documents EP 126459, υδ 2006211780, υδ 2005156344, υδ 6783710 and νΟ 2008141766, the contents of which are included in the present invention.

Examples

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In all examples, the polystyrene melt index is measured at 200 ° C. and a load of 5 kg (ΌΙΝ Ι 8Θ 1133).

Example 1. The standard, ΜΡΙ = 7.

A mixture containing 99 parts of polystyrene (Μν = 170 kg / mol, polydispersity coefficient (ΡΙ) = 2.3) and 1 part of talc from Li / Spas® are fed to the extruder. 6 weight % pentane (80/20 n- / isopentane) is introduced into the extruder through a special conveyor. The flow index for this melt is 7 g / 10 min in accordance with Ι Ι 8Ο 1133. At the end, the sample is granulated at the outlet of the forming head using an underwater granulator. The recovered granules, the diameter of which is in the range of 0.3-2 mm, are then treated with a coating agent such as zinc stearate and, optionally, mono-, bi- or tri-stearate glycerol. The treated granules are subjected to preliminary foaming under the influence of steam at 100 ° C, incubated for 1 day and, finally, used to form a plate. After 1 day, the density of the plate, determined by weighing the plate and measuring its size, is 19 g / l. After at least 30 days of exposure, the sample is subjected to a compression test. The value of stress at 10% strain, evaluated according to the standard ΕΝ826, is 113 kPa. The thermal conductivity of the plate, measured in accordance with the standard Ι8Ο 8301, is 0.035 W / mK.

Example 2. The standard ΜΡΙ = 8.5.

A mixture containing 99 parts of polystyrene (Μν = 155 kg / mol, ΡΙ = 2.2) and 1 part of talc from Li / Spas®. served in the extruder. 6 wt.% Pentane (80/20 n- / isopentane) is introduced into the extruder through a special conveyor. The flow index for this melt is 8.5 g / 10 min in accordance with ΌΙΝ Ι 8Ο 1133. At the end, the sample is granulated at the outlet of the forming head using an underwater granulator. The recovered granules, the diameter of which is in the range of 0.3-2 mm, are then treated with a coating forming agent such as zinc stearate and, optionally, mono-, bi- or tri-stearate glycerol. The treated granules are subjected to preliminary foaming under the influence of steam at 100 ° C, incubated for 1 day and, finally, used to form a plate. After 1 day, the density of the plate, determined by weighing the plate and measuring its size, is 19.1 g / l. After at least 30 days of exposure, the sample is subjected to a compression test. The value of stress at 10% strain, estimated according to the standard ΕΝ826, is 101.4 kPa.

Example 3. In accordance with the present invention, Ρ8 + 0.5% ΡίΒ, ΜΡΙ = 8.5.

Foaming granules are obtained under the same conditions as described in Example 1, except that the initial mixture contains 98.5 parts of polystyrene (Μν = 170 kg / mol, ΡΙ = 2.3), 1 part of talc from Li / Spas® and 0.5 parts of polyisobutene OY88ora1 1000 from ΒΑ8Ρ. OH88ora1 1000 is polyisobutene with Μη = 1000. The melt flow index is 8.5 g / 10 min, in accordance with Ι Ι8Ο 1133. The plate obtained after the preliminary foaming and molding steps has a density of 19.9 g / l. After at least 30 days of exposure, the sample is subjected to a compression test. The value of stress at 10% deformation, evaluated according to the standard ΕΝ826, is 117.3 kPa.

Comparative example 3. Ρ8 + 1% oil Ρτ ^ οΐ, ΜΡΙ = 8.1.

Foaming granules are obtained under the same conditions as described in Example 2, except that the initial mixture contains 98 parts of polystyrene (Μν = 170 kg / mol, ΡΙ = 2.3), 1 part of talc from Ln / Spas® and 1 teaspoon oil Ρπιηοΐ 352 from Εχχοη. Ρπιηοΐ 352 is a light mineral oil (CA8 number: 8042-47-5 ΕINΕС8 number: 232-455-8) with an average molecular weight of 480 (Α8ΤΜ Ό 2502) and a percentage of carbon paraffin / naphthenic / aromatic fractions 66/34 / 0 (Α8ΤΜ Ό 2140). The melt flow index is 8.1 g / 10 min, in accordance with ΌΙΝ Ι 8Ο 1133. The plate obtained after the preliminary foaming and molding steps has a density of 18.8 g / l. After at least 30 days of exposure, the sample is subjected to a compression test. The value of stress at 10% strain, estimated according to the standard ΕΝ826, is 103.8 kPa.

Example 4. In accordance with the present invention, Ρ8 + 1% ΡίΒ, ΜΡΙ = 9.

Foaming granules are prepared under the same conditions as described in Example 1, except that the initial mixture contains 98 parts of polystyrene (Μν = 170 kg / mol, ΡΙ = 2.3), 1 part of talc from Li / Spas® and 1 h polyisobutene OH88ora1 1000 from ΒΑ8Ρ. The flow index for this melt is 9 g / 10 min, in accordance with Ι Ι 8Ο 1133. The plate obtained after the preliminary foaming and molding steps has a density of 19.5 g / l. After at least 30 days of exposure, the sample is subjected to a compression test. The value of stress at 10% strain, estimated according to the standard ΕΝ826, is 112.2 kPa.

Comparative example 4. Ρ8 + 2% Ρπιηοΐ 352, ΜΡΙ = 8.9.

Foaming granules are prepared under the same conditions as described in Example 3, except that the initial mixture contains 97 parts of polystyrene (Μν = 170 kg / mol, ΡΙ = 2.3), 1 part of talc from Ln / Spas® and 2 parts oil Ρπιηοΐ 352 from 2χχοη. The yield index for this melt is 8.9 g / 10 min in accordance with Ι Ι 8Ο 1133. The plate obtained after the preliminary foaming and molding steps is performed, 7,029,941 has a density of 20 g / l. After at least 30 days of exposure, the sample is subjected to a compression test. The value of stress at 10% strain, estimated according to the standard ΕΝ826, is 99 kPa.

Example 5. In accordance with the present invention, P8 + 3% CB + 1% ΡίΒ, ΜΡΙ = 9.3.

Foaming granules are obtained under the same conditions as described in Example 3, except that the initial mixture contains 95 parts of polystyrene (Μ \ ν - 170 kg / mol, ΡΙ - 2.3), 1 part of talc from b / ets®, 1 part of polyisobutene С8888ор1 1000 from VL8R and 3% of carbon black Еikасо 2600 from Т1тса1. The flow index for this melt is 9.3 g / 10 min, in accordance with Ι Ι 8Ο 1133. The plate obtained after the preliminary foaming and molding steps has a density of 20.2 g / l. After at least 30 days have passed, the sample is subjected to a compression test. The value of stress at 10% strain, evaluated according to the standard ΕΝ826, is 116 kPa. The thermal conductivity of the plate, measured in accordance with the standard Ι8Ο 8301, is 0.0318 W / mK.

Comparative example 5. + 3% CB + 2% Ppto1 352 ΜΡΙ = 10.2.

Foaming granules are obtained under the same conditions as described in Example 3, except that the initial mixture contains 95 parts of polystyrene (M \ y = 170 kg / mol, ΡΙ = 2.3), 1 part of talc from L / ets®. 2 parts of oil Рпто1 352 from Еххоп and 3% of carbon black Еikасо 2600 from Т1тса1. The yield index for this melt is 9.6 g / 10 min, in accordance with ΌΙΝ Ι 8Ο 1133. The plate obtained after the preliminary expansion and molding steps has a density of 20 g / l. After at least 30 days of exposure, the sample is subjected to a compression test. The value of stress at 10% strain, estimated by the standard ΕΝ826, is 95.1 kPa. The thermal conductivity of the plate, measured in accordance with the standard Ι8Ο 8301, is 0.0324 W / mK.

Crmmer Polystyrene M " (kg / mol) Character additives Koli'the the state additives (%) Carbon content (%) ΜΪΙ ¹ rpm) Density slabs (g / l) ² compressive strength at 10% lnneknon deformation (kPa) one Reference 170 Bel additives 0 7 nineteen 113 2 Reference 166 Beth additives - {> 8 5 19.1 101,4 3 170 ΡίΒ 0.5 0 8.5 19.9 117.3 Compare 3 170 Oil I 0 8 1 18.8 103.8 4 170 ΡίΒ I 0 nine 19.5 112.2 Compare 4 170 Oils 2 0 8.9 twenty 99 5 170 ΡίΒ one 3 9.3 20,2 116 Compare 5 170 Oil 2 3 9.6 twenty 95.1

¹ Measured at 20 ° C with a weight of 5 kg, in accordance with the standard ϋΙΝ Ι8Ο 1133 ⁵ Measured in accordance with the standard ΕΝ826

Discussion examples

Example 1 illustrates the preparation of EP8 white granules from standard grade polystyrene by extrusion using an underwater granulator. Good melt flow control is a critical factor in facilitating melt cutting and producing spherical granules with a narrow particle size distribution. The melt flow index of the polystyrene used (ΜΡΙ = 7 g / 10 min, 170 kg / mol, ΡI = 2.3) is too low and requires a higher granulation temperature in order to prevent clogging of the holes in the plate of the forming head. However, an increase in temperature leads to the formation of granules of irregular shape and a wide particle size distribution. Therefore, the proposed strategy is to find a way to reduce the viscosity of the melt, which will facilitate granulation and prevent clogging of the holes or deformation of the granules.

One way to reduce the viscosity of the melt is to choose a low molecular weight P8, as shown in Example 2 (ΜΡΙ = 8.5 g / 10 min, 155 kg / mol, ΡI = 2.2). Such melt flowability greatly facilitates granulation and allows very regular granules to be obtained. Nevertheless, the resulting plates have weaker compressive strength (101.4 kPa) due to the lower P у · · ·.

Another classic way to reduce the viscosity of the melt is to add a certain amount of oil (see comparative examples 3 and 4). With the addition of 1 and 2 wt.%, Oil ΜΡΙ successfully rises to 8.1 and 8.9 g / 10 min, respectively, which greatly facilitates underwater granulation. However, the added oil reduces the mechanical strength of the foam (103.8 and 99 kPa, respectively).

The present invention has found that the addition of polyisobutene can lead to an increase in the melt flow index P8 without affecting the final mechanical strength of the foam. In fact, as shown in examples 3 and 4, the addition of 0.5 and 1 weight. % P1B leads to ΜΙ 8.5 and 9 g / 10 min, respectively. This higher melt flow facilitates the underwater granulation step (no blockage is observed). Moreover, the mechanical strength of the obtained plates is similar to the strength of the plates in example 1, where the plasticizer is not added (117.31 and 112.2 kPa, respectively). Thus, the addition of polyisobutene facilitates the granulation process without adversely affecting the final mechanical properties of the foam.

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The same experiment was carried out with the addition of a filler, namely carbon black, which can reduce the thermal conductivity of the foam, for insulation purposes. In Example 5, with the addition of 1% ΡίΒ and 3% carbon black (9.3 g / 10 min), a satisfactory ΜΡΙ is obtained. The compression resistance of the resulting plates does not depend on these additives (116 kPa), and the thermal conductivity of the plates decreases (0.0318 W / mK compared to 0.035 W / mK without carbon black, see example 1). In contrast, Comparative Example 5 demonstrates that the mechanical resistance of foams containing 1% oil and 3% carbon black is reduced (95.1 kPa), while thermal conductivity remains acceptable (0.0324 W / mK).

Claims (5)

CLAIM 1. A method of increasing the melt flow index of a foamable vinyl aromatic polymer while maintaining the same or obtaining higher compressive strength at 10% linear deformation, comprising the steps of a) provide a vinyl aromatic polymer in a molten state; b) injected into the polymer matrix 1-10 wt.%, based on the polymer (a), a foaming agent and c) 0.1-5 wt.% are introduced and uniformly distributed in the polymer matrix, based on polymer (a), polyisobutene ΡίΒ, where the relative content ΡίΒ is adjusted to increase the melt flow index (ΜΡΙ), measured at 200 ° C and weighing 5 kg in accordance with ΌΙΝ ΙδΟ 1133, from the initial index to the final index, so that the compressive strength at 10% linear strain, measured in accordance with the standard ΕΝ826, for foam obtained using the specified expanded onto vinylaromatic polymer with final in eksom, was the same or higher than the foam obtained by said expandable vinylaromatic polymer with an initial index. 2. The method according to claim 1, where используют with a number average molecular weight of 500 to 5000 is used. 3. The method according to claim 2, where используют is used with a number average molecular weight in the range from 900 to 3000. 4. The method according to any one of claims 1 to 3, wherein polystyrene, such as crystalline polystyrene and high-strength polystyrene (ΗίΡδ), is used as a vinyl aromatic polymer. 5. The method according to any one of claims 1 to 4, further comprising b) the introduction and uniform distribution in the polymer matrix of up to 20 wt.%, based on the polymer (a), of one or more fillers other than ΡίΒ.