RU2799780C2 - Expandable vinyl aromatic polymer composition with improved mechanical and insulating properties - Google Patents

Abstract

FIELD: polymers.

SUBSTANCE: present invention relates to an expandable vinyl aromatic polymer composition having improved mechanical and insulating properties, which comprises: d) from 60% to 96% wt. The present invention relates to the group of inventions: an expandable vinyl aromatic polymer composition, a continuous bulk process for producing an expandable vinyl aromatic polymer composition, and an expanded product. Expandable vinyl aromatic polymer composition comprises: 60-96% wt. vinyl aromatic polymer (a); 3-10% wt. expanding agent (b); 1-30% wt. vinylaromatic copolymer (c), comprising from 1 to 10% wt. rubber component as a dispersed phase. A continuous bulk process for producing an expandable vinyl aromatic polymer composition includes the following steps: mixing the vinyl aromatic polymer (a) and the vinyl aromatic copolymer (c) in the form of granules, powdered or pre-melted; optionally, if melting has not yet occurred, bringing the polymer mixture to a temperature higher than or equal to the melting point of the vinyl aromatic polymer (a) and copolymer (c); including at least one expanding agent (b) in the molten polymer mixture forming the vinyl aromatic polymer composition; mixing the polymer composition thus obtained using static or dynamic mixing elements; sending the polymer composition obtained after mixing to the matrix plate with cutting under pressure.

EFFECT: making an expandable vinyl aromatic polymer composition with improved mechanical and thermal insulation properties, its production method, as well as products that can be obtained from such a composition.

18 cl, 1 dwg, 1 tbl, 9 ex

Description

Brief summary of the invention

The present invention relates to an expandable vinyl aromatic polymer composition having improved mechanical and insulating properties, which contains:

a) from 60% to 96% wt. vinyl aromatic polymer (a);

b) from 3% to 10% wt. expanding agent (b);

c) from 1% to 30% wt. vinylaromatic copolymer (c), containing from 1% to 10% wt. a rubber component as a dispersed phase;

provided that the sum of (a), (b) and (c) is 100% wt.; as well as the method of its preparation and the corresponding use, and products that can be obtained from this composition.

The field of technology to which the invention belongs

The present invention relates to an expandable vinyl aromatic polymer composition having improved mechanical and thermal insulation properties, a production method for obtaining it, as well as to products that can be obtained from such a composition.

Said compositions impart to final articles containing them a high impact energy absorption rate such as "damping" effect, flexibility, excellent compressive properties and a soft feel, as well as good thermal insulation characteristics. The main field of application of the described and claimed compositions is the field of application as a flexible packaging material in both the food and industrial sectors, where softness to the touch, shock damping properties and thermal insulation are required.

The composition according to the invention achieves a balance between mechanical properties (flexibility), insulating ability, pleasantness (softness) to the touch and a high degree of sintering, which opens up new market segments from which standard expandable polystyrene (EPS) is currently excluded.

In this patent application, all operating conditions included in the text should be considered as preferred conditions, even in the absence of an unambiguous indication of this fact.

For the purposes of this description, the terms "comprises" or "includes" also encompass the terms "consists of" or "essentially consists of".

For the purposes of this description, range expansions will always include endpoints unless otherwise noted.

Expandable polymers are usually produced in the form of grains or granules, which, as a result of the action of heat supplied, for example, with water vapor, are first expanded to the desired density, and then, after a certain aging time, sintered in closed molds to obtain blocks or desired end products.

Expandable beads can be prepared using an aqueous suspension batch polymerization process. This process, well known to those skilled in the art, includes the following steps:

dispersing the liquid vinyl aromatic monomer in an aqueous medium using suspending agents;

adding polymerization catalysts and polymerizing the vinyl aromatic monomer in a stirred heated reactor;

adding an expanding agent at a certain level of monomer conversion;

completion of polymerization;

unloading, washing, drying and screening of the resulting grains. The grain diameter usually ranges from 0.1 to 3 mm.

This slurry process can produce a good quality product, but it has several disadvantages, such as:

a very wide distribution of grain sizes, which implies the need to separate different fractions by sieving and discarding products of the wrong size;

significant restrictions on the production of specialty products, such as colored grains and/or grains containing heterogeneous fillers or additives, such as nucleating agents and/or fire retardants, because they are difficult to include in grains or they can inhibit polymerization.

In the state of the art, suitable packaging compositions are prepared using very costly methods of aqueous suspension or granulation followed by subsequent aqueous suspension impregnation.

The aqueous slurry process produces batches of granules having a specific average diameter ranging from the smallest fractions (0.1-0.3 mm) to the largest fractions (greater than 2 mm). Finer fractions are used in gasified molding industries for both food and industrial packaging. Large fractions are used for thermal insulation. For flexible packaging, which is the scope of products containing the compositions to which this patent application relates, only fractions are used, characterized by weighted average diameters in the ranges of 0.4 - 0.6 mm, 0.6 - 0.9 mm, 0.9 - 1.2 mm and 1.2 - 1.6 mm, depending on the type of product.

The aqueous slurry process produces large quantities of undesirable fractions even when sophisticated techniques are used such as the use of Na sulfate and other additives to reduce the particle size distribution. Fractions smaller or larger than the fraction in the range of 0.4 to 1.6 mm inevitably produced when using a suspension cannot be used.

Granulation followed by subsequent impregnation is also costly, since long impregnation cycles in the reactor are required to penetrate the expanding agent into the center of the granule. Using this technology, only the desired fraction of granules is obtained, but two installations are required for this: a polymerization and granulation installation and a post-impregnation installation. The impregnation system is very similar to the slurry system, with the difference that granules are suspended rather than droplets of styrene monomer. Therefore, impregnation with an expander is much more costly, since the polymer pellet is already present, which must be softened above the softening point or Tg (glass transition temperature), then spherical, and then impregnated. This step is critical because if the expander does not reach the center of the pellet, the final foam will have a center that is only slightly expanded or in some cases still compacted. The presence of such a poorly expanded center leads to breakage of the cables for the cutting heads, followed by an emergency stop of the process plant.

The Tg value of a polymeric material is determined by the temperature at which a second-order phase transition between the solid and liquid states of the polymeric composition occurs, which corresponds, for example, to the description in "Principles and applications of Thermal Analysis", Paul Gabbott, Blackwell Publishing Ltd., 2008.

US 6,232,358 (published 1999) discloses a rubber-modified styrene resin composition that is capable of producing a foam with a high degree of expansion, excellent impact resistance and flexibility, and satisfactory appearance. As a production method, this document provides an example of granulation followed by impregnation, but this method is expensive because the styrene resin is first obtained, then extruded, and then the granules are suspended in water and impregnated for 5 hours.

The penetration of the expanding agent into the center of the granule requires the use of long impregnation cycles (5 hours) in the reactor. Using this technology, only the desired fraction is obtained, but two units are required - a polymerization/granulation unit and a post-impregnation unit. Therefore, impregnation with an expander is much more costly, since polymer pellets are already available, which must be softened at a temperature higher than Tg, then made spherical, and then impregnated. This step is critical because if the expanding agent does not reach the center of the pellets, the final expanded material will have a center that is only slightly expanded or in some cases still compacted. The presence of such a poorly expanded center leads to breakage of the cables for the cutting heads, followed by an emergency stop of the process plant.

Another example of the same manufacturing process is EP 0722974 (published 1996) which discloses expanded rubber modified styrene beads and rubber modified styrene resin products.

One further example is EP 1266929 (published in 2012) which discloses expandable polystyrene resin particles which are expandable polystyrene resin particles (d) comprising modified polystyrene resin particles (c) containing an expanding agent (e), modified polystyrene resin particles (c) containing polystyrene resin and rubber polymer particles (b), dispersed in this resin, wherein the rubber polymer particles (b) are uniformly dispersed in the continuous phase of the polystyrene resin or are in a state in which the density of the particles (b) is higher in the core of the resin particle than in its surface layer, and the modified polystyrene resin particles (c) are modified polystyrene resin particles obtained by impregnating a mixture of monomers substantially containing styrene monomer and conjugated a diene monomer, and containing a styrene monomer in a larger amount than the amount of the conjugated diene monomer in the polystyrene resin particles (a), and carrying out copolymerization.

Another example is DE 19710442 (published in 1998), which describes an expandable styrenic polymer (I) containing:

(A) a polymer matrix containing from 70 to 95% wt. polystyrene or styrene copolymer, comprising up to 50% comonomers, and from 5 to 30% wt. styrene-butadiene block copolymer;

(B) 1 - 15% wt. (with respect to (A)) a volatile expanding agent; and optionally (C) conventional additives.

In contrast, US publication 5,166,221 (EP 0425973, published in 1991) discloses expandable styrenic polymers comprising from 10 to 90% wt. styrene-diene star-shaped block copolymer, comprising from 2 to 45% wt. diene, and from 1 to 10% wt. C3-C6 hydrocarbons as an expanding agent, which can be processed to produce foams that are highly resistant to aromatics. As one example, the document proposes a production process that involves aqueous suspension polymerization, but using this technology produces large amounts of undesirable fractions, even though sophisticated techniques are used to reduce distribution (for example, the use of Na sulfate and other additives). Smaller or larger fractions, inevitably produced when using a suspension, cannot be used.

Another example of aqueous suspension polymerization is EP 0872513 (published in 1998), which describes a styrenic polymer expandably modified with rubber (I) comprising:

(A) a continuous phase of polystyrene or styrene copolymer, including up to 50% wt. comonomer;

(B) 5 - 30% wt. (based on the raw polymer mixture) of dispersed rubber particles and (C) 2 to 15 parts by weight (based on 100% by weight of the polymer mixture) poorly bonding expanding agent.

In contrast, WO 1994/025516 (published in 1994) describes expanded particles for a rubber-modified styrenic polymer comprising a plurality of closed cells formed by cell walls that form a matrix for the particles, where each of the cell walls includes two surfaces separated by a distance equal to the thickness of the cell wall. The production method includes extruding together with granulation in water.

One example of the same manufacturing process is US 3,558,534 (published 1971), which describes expandable aromatic alkenyl polymers that do not acquire or retain a static charge and are formed by incorporating a small amount of rubber polymer into the expandable polymer.

One further example is JP 2004115690 (published 2004) which describes a method for making a good quality expandable particle that does not contain foam using a styrenic type resin, in particular a recycled (i.e. recycled) styrene type resin product.

Also known is the technology of continuous production in mass (for example, the publication EP 1541621, published in 2005) in accordance with the following steps:

1. incorporating an expanding agent into the rubber-containing vinyl aromatic polymer using a static or dynamic mixer;

2. cooling the molten polymer to 150 - 200°C;

3. discharge through a die plate (mouthpiece) with nozzles having a diameter of at least 1.5 mm;

4. granulation under water at a pressure between 5 and 20 bar.

Detailed description of the invention

The purpose of the present invention is to provide a vinyl aromatic polymer composition suitable for use in flexible packaging.

In one preferred aspect of the present invention, it is possible to obtain such compositions in a single step using continuous bulk processing technology.

Thus, the subject of the present invention is an expandable vinyl aromatic polymer composition with improved mechanical and insulating properties, comprising:

a) from 60% to 96% wt. vinyl aromatic polymer (a);

b) from 3% to 10% wt. expanding agent (b);

c) from 1% to 30% wt. vinylaromatic copolymer (c), containing from 1% to 10% wt. a rubber component as a dispersed phase;

provided that the sum of (a), (b) and (c) is 100% wt.

The term "comprising" and its derivatives is not intended to exclude the possibility of the presence of any additional components, steps or techniques, whether they will be disclosed in this text or not. For the avoidance of any doubt, all compositions claimed in this text using the term "comprising" may include any additives, auxiliary activators or other additional compounds of a polymeric or other type, unless otherwise indicated.

Additional objects and advantages of the present invention will become clearer upon reading the following description of the invention, presented by way of example only and not as a limitation, which illustrates the preferred embodiments of the present invention.

Fig. 1 illustrates damping tests related to the invention examples and comparative examples.

The damping property of a package expresses its ability to absorb energy after an impact. Performance is expressed in terms of "shock load factor" (maximum deceleration expressed in multiples of the acceleration of gravity g (in m/s ² ) after impact as a function of "static stress" (force per unit surface area in kPa)).

For the purposes of this invention, the term "vinyl aromatic polymer (a)" will mean a polymer obtained from at least 65% wt. vinyl aromatic monomer.

Vinyl aromatic monomers that can be used to produce vinyl aromatic polymer (a) used in the compositions described and claimed in the present invention are described by the general formula (I):

In formula (I), R represents a hydrogen atom or a methyl group; n is zero or an integer in the range from 1 to 3, Y is selected from a halogen atom, preferably chlorine or bromine atoms, chloromethyl, an alkyl group or alkoxy group containing from 1 to 3 carbon atoms.

Preferred vinylaromatic monomers of formula (I) are selected from styrene, α-methylstyrene, methylstyrene, ethylstyrene, vinyltoluene isomers, ethylstyrene isomers, propylstyrene isomers, chlorostyrene isomers, methylchlorostyrene isomers, methoxystyrene isomers, acetoxystyrene isomers, hydroxystyrene isomers , methylhydroxystyrene isomers and mixtures thereof. More preferably, styrene and α-methylstyrene may be selected from these vinyl aromatic monomers. Styrene is the predominant vinyl aromatic monomer and preferably makes up at least 50% of the mixture of vinyl aromatic monomers used to produce the vinyl aromatic polymer (a), more preferably at least 75%, even more preferably at least 85%. Another preferred comonomer is α-methylstyrene.

Vinyl aromatic monomers described by the general formula (I) can be used individually, in a mixture or in a mixture containing up to 35% wt. other copolymerizable vinyl monomers.

Preferred copolymerizable vinyl monomers are selected from (meth)acrylic acid, maleic anhydride, (meth)acrylic acid alkyl esters containing from 1 to 18 carbon atoms, amides and (meth)acrylic acid nitriles. Among the (meth)acrylic acid esters mentioned, preferred corresponding compounds are those selected from ethyl acrylate, methyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, dodecyl methacrylate, stearyl acrylate, stearyl methacrylate, glycidyl methacrylate, ethylene glycol dimethacrylate and mixtures thereof.

Among the (meth)acrylic acid nitriles mentioned, the preferred corresponding compounds are those selected from acrylamide, methacrylamide, dimethylaminoethyl methacrylate, acrylonitrile, methacrylonitrile. Other copolymerizable vinyl comonomers may be butadiene and divinylbenzene.

The weight average molecular weight MW of the polymer and/or copolymer (a) as measured using the gel permeation chromatography (GPC) technique described in the experimental part (ASTM method D5296-11 GPC PS) is in the range between 90 kDa and 300 kDa.

An MW value of less than 90 kDa results in excessively high fluidity, which results in grain collapse during the expansion process. An MW value of more than 300 kDa results in insufficient expansion and an unusable final density of the foam portion.

Compositions according to the present invention may include an amount of vinyl aromatic polymer (a) in the range of 60 to 96 wt%, preferably 67 to 88 wt%, more preferably 69 to 83 wt%, as compared to the sum of (a), (b) and (c) as defined above.

For the purposes of this invention, a vinyl aromatic copolymer (c) is defined as a copolymer derived from at least one vinyl aromatic monomer as defined above and containing a rubber component as a discontinuous phase.

Some examples of vinyl aromatic copolymer (c) are Edistir®850E, Edistir®ICE R830D, Edistir®RC600 manufactured and marketed by Versalis s.p.a.

The rubber component used in the vinyl aromatic copolymer (c) is present in an amount ranging from 1% to 10% wt. and may be selected from polybutadiene, polyisoprene, butadiene and/or isoprene copolymers with styrene or other vinyl monomers.

Some examples of suitable rubber components are polybutadiene, such as the products "Intene® 40", "Intene® 50" and "Intene® 60" manufactured and marketed by Versalis s.p.a.

Alternatively, styrene-diene block copolymers are also on the market, such as the products "SOLPRENE® 1205", "SOLPRENE® S1430", "SOLPRENE® 308" and "SOLPRENE® 314" manufactured and marketed by Dynasol, or the product "Europrene® SOL B 183" manufactured and marketed by Versalis s.p.a.

The copolymer (c) can be obtained by any known method of suspension polymerization, block emulsion polymerization or continuous bulk polymerization.

In the case where the amount of polybutadiene dispersed is not specified, it can be suitably determined using the iodometric titration method described below in the experimental section.

In one preferred aspect of the present invention, the vinyl aromatic copolymer (c) is obtained by prepolymerization of the vinyl aromatic monomer in the presence of suitable free radical initiators and a rubber component in the first reactor until a conversion of less than 50% wt. supplied monomers. The polymerization is then completed in one or more successive reactors until the complete polymerization of the monomers. The resulting polymer is then devolatized and granulated.

Compositions according to the present invention may contain from 1 to 30% by weight, preferably from 9 to 25% by weight, more preferably from 13 to 24% by weight, even more preferably from 15 to 25% by weight, and even more preferably from 17 to 22% by weight. vinyl aromatic copolymer (c) compared to the sum of (a), (b) and (c) as defined above.

The amount of the rubber component dispersed in the vinyl aromatic copolymer (c) may vary between 1 and 10 wt.%, preferably between 2 and 10 wt.%, more preferably between 3 and 9 wt. .

Therefore, it follows that in the case where the copolymer (c) is present in an amount of 1% by mass, the rubber component present in an amount of 1% to 10% by mass. compared with the copolymer (c), may be present in an amount in the range between 0.01% and 1% wt. compared to the sum of (a), (b) and (c) as defined above.

Similarly, in the case where the copolymer (c) is present in an amount of 30% wt., the rubber component present in an amount of from 1% to 10% wt. compared with the copolymer (c), may be present in an amount of from 0.3% to 3% wt. compared to the sum of (a), (b) and (c) as defined above.

Similarly, as demonstrated in the examples, when the copolymer (c) is present in an amount of 15%, 20%, 25% wt. from the sum of (a), (b) and (c) as defined above, the rubber component present at 7%, 7.5%, 8.5% will correspond to the following values with respect to the sum of (a), (b) and (c) as defined above.

Example % polymer (c) relative to the sum of (a), (b) and (c) % PB in polymer (s) % PB in relation to the sum of (a), (b) and (c) Example 1 20 7 1.4 Example 2 25 7 1.75 Example 3 15 7 1.05 Example 4 20 8.5 1.7 Example 5 20 7.5 1.5 Example 8 9 7.5 0.675

In one preferred aspect of the present invention, the rubber component dispersed in the vinyl aromatic copolymer (c) is polybutadiene (PB) and/or styrene-diene block copolymers.

Compositions according to the present invention may comprise from 3% to 10% by weight, preferably from 3% to 8% by weight, of at least one expanding agent (b).

In the compositions to which the invention relates, any expanding agent that can be included in the polymer can be used.

Preferably, the expanding agents may be liquid substances having a boiling point in the range between 10° C. and 100° C. at atmospheric pressure; preferably between 20°C and 60°C. Expanding agents that can be used in this invention are selected from aliphatic or cycloaliphatic hydrocarbons containing from 3 to 6 carbon atoms; for example n-pentane, isopentane, cyclopentane, butane, isobutane and mixtures thereof; or halogenated derivatives of aliphatic hydrocarbons containing from 1 to 3 carbon atoms, such as dichlorodifluoromethane, 1,2,2-trifluoroethane and 1,1,2-trifluoroethane; or carbon dioxide.

Compositions according to the present invention may include expanding agent (b) in an amount of 3 to 10 wt%, preferably 3 to 8 wt%, more preferably 4 to 7 wt%, relative to the sum of (a), (b) and (c) as defined above.

To help retain the expander in the polymer matrix (a), additives can be used that can form weak bonds (eg, hydrogen bonds) or strong bonds (eg, in the case of acid-base adducts) with the expander. Preferably, these additives are selected from methanol, isopropyl alcohol, dimethyl carbonate, or derivatives containing an amino group. Additional additives (typically traditional vinyl aromatic polymers) can be added to the compositions of the present invention, such as nucleating agents such as polyethylene waxes or talc, antioxidants, pigments, stabilizers, antistatic agents, and anti-adhesion agents.

In one preferred aspect of the present invention, polymeric compositions having improved mechanical and insulating properties comprise:

a) from 67% to 88% wt. vinyl aromatic polymer (a);

b) from 3% to 8% wt. expanding agent (b);

c) from 9% to 25% wt. a vinyl aromatic copolymer (c) containing 2% to 10% rubber component as a dispersed phase;

provided that the sum of (a), (b) and (c) is 100% wt.

In one further preferred aspect of the present invention, the polymeric compositions comprise:

a) from 69% to 83% wt. vinyl aromatic polymer (a);

b) from 4% to 7% wt. expanding agent (b);

c) from 13% to 24% wt. a vinyl aromatic copolymer (c) containing 3% to 9% of a rubber component as a dispersed phase;

provided that the sum of (a), (b) and (c) is 100% wt.

In yet another preferred aspect of the present invention, the polymeric compositions comprise:

a) from 69% to 81% wt. polystyrene;

b) from 4% to 6% wt. expanding agent (b);

c) from 15% to 25% wt. copolymer consisting of high-impact polystyrene containing from 4% to 9% wt. rubber component;

provided that the sum of (a), (b) and (c) is 100% wt.

In yet another aspect of the present invention, the polymeric compositions comprise:

a) from 72% to 79% wt. polystyrene;

b) from 4% to 6% wt. mixtures of expanding agents (b);

c) from 17% to 22% wt. copolymer consisting of impact-resistant polystyrene containing from 7% to 8.5% wt. rubber component;

provided that the sum of (a), (b) and (c) is 100% wt.

Polymer compositions corresponding to the present invention can be obtained by methods known in the state of the art.

In one aspect of the present invention, the polymeric compositions of the present invention are conventionally produced in a continuous bulk process comprising the following steps in this order:

i. mixing a vinyl aromatic polymer (a) as defined above and a vinyl aromatic copolymer (c) in the form of granules, powdered or pre-melted,

ii. optionally, if melting has not yet occurred, bringing the polymer mixture to a temperature that is higher than or equal to the melting point of the vinyl aromatic polymer (a) and copolymer (c);

iii. the inclusion of at least one expanding agent (b) in the molten polymer mixture forming a vinyl aromatic polymer composition corresponding to the present invention;

iv. mixing the polymer composition thus obtained using static or dynamic mixing elements;

v. supplying the polymer composition obtained after mixing to the matrix plate with cutting under pressure.

One cutting die plate used is, for example, the corresponding plate described in US 7,320,585 in conjunction with a cutting system of the "Spray Nozzle System" type. The expandable granules/grains to which the invention relates can also be made using another type of die plate where the polymer is cut in a granulation chamber full of water, a system known as "underwater" cutting. In such a case, the polymer remains completely immersed in water during the cutting step and the water pressure in the granulation chamber is more than 300 kPa.

At the end of the continuous bulk process, the resulting final compositions of the present invention are in the form of polymer pellets having a spheroidal profile and various average diameters which can be used according to the nature of the individual product and are typically in the range of 0.4-0.6 mm, 0.6-0.9 mm, 0.9-1.2 mm or 1.2-1.6 mm.

In one embodiment of the present invention, the polymeric compositions of the present invention, comprising:

a) from 60% to 96% wt. vinyl aromatic polymer (a);

b) from 3% to 10% wt. expanding agent (b);

c) from 1% to 30% wt. vinylaromatic copolymer (c), containing from 1% to 10% wt. a rubber component as a dispersed phase;

provided that the sum of (a), (b) and (c) is 100 wt.%, can be obtained using a continuous method in bulk, comprising the following steps in this order:

i. mixing one polymer (a) as defined above and/or a vinyl aromatic copolymer (c) in the form of granules, powder or pre-melted,

ii. optionally, if melting has not yet occurred, bringing the polymer mixture to a temperature higher than or equal to the melting point of the vinyl aromatic polymer (a) and copolymer (c);

iii. the inclusion of at least one expanding agent (b) in the molten polymer mixture forming a vinyl aromatic polymer composition corresponding to the present invention;

iv. mixing the polymer composition thus obtained using static or dynamic mixing elements;

v. supplying the polymer composition obtained after mixing to the matrix plate with cutting under pressure.

Several illustrative examples are provided below to better understand the invention and its scope. These examples do not limit the scope of the present invention in any way.

experimental part

Determination of molecular weight (MW) and molecular weight distribution (MWD) using the GPC method

The compositions of the present invention are characterized by a weight average molecular weight (MW) in the range between 90 and 300 kilodaltons as measured using high performance molecular size exclusion chromatography in accordance with ASTM D5296-11 and exhibit a flow index (melt flow index MFI at 200°C, 5 kg) in the range between 2.5 and 50.

The flow index is measured in accordance with ISO 1133, fourth edition, 2005.

Molecular weight distribution is measured using high performance molecular size exclusion chromatography in accordance with ASTM D5296-11 using a refractive index detector (RD), and the measurement is carried out on the polymer after separation from the dry residue and subsequent precipitation.

Polybutadiene level determination using iodometric titration

Iodometric titration is carried out using a 785 DMP Titrino Metrohm Titrator according to this method.

(a) Analysis of a blank sample as follows

1) Receipt (time 15 min)

Add 20 ml CHCl ₃ and a magnetic stirrer to a 100 ml Erlenmeyer flask.

2) Addition of Weiss reagent (time 15 min)

Addition of 2.5 ml Wijs reagent using a titrator.

Filling the neck with potassium iodide and shaking on a rotating plate for 10 minutes, possibly in the dark.

3) Definition (time 15 min)

Removing the potassium iodide inlet cap, mixing and adding H ₂ O.

Titration with sodium thiosulfate with vigorous stirring.

To start the titration, press the START key, enter the amount of Weiss reagent aliquot added to the blank, and change the unit from grams to ml.

Determination Vb = ml of thiosulfate solution used in the blank test.

(b) Sample analysis

1) Receipt (time 25 min)

Weigh approximately 0.25 g of vinyl aromatic copolymer (c) and approximately 0.05 g (polybutadiene) into a 100 ml Erlenmeyer flask while recording P=mass of polymer sample (g).

Adding 20 ml CHCl ₃ and a magnetic stirrer.

Arrangement of an Erlenmeyer flask on a rotating plate to dissolve the polymer (~20 min).

2) Addition of Weiss reagent (time 20 min)

Addition of 5 ml Wijs reagent using a titrator.

Filling the neck with potassium iodide and shaking on a rotating plate for 15 minutes, possibly in the dark.

3) Definition (time 15 min)

Removing the potassium iodide inlet cap, mixing and adding H ₂ O.

Titration with sodium thiosulfate with vigorous stirring.

To start the titration, press the START key, enter the name of the sample (ID 1), the value of the added aliquot of the Weiss reagent (ID 2) and the mass of the sample.

Definition Vc = ml of thiosulfate solution used for the sample.

Result Expression (% RV)

,

Where:

V _b = ml of thiosulfate solution used in the blank test

V _c = ml of thiosulfate solution used for the sample

= normality of thiosulfate solution (0.1 N)

PE _PBu = equivalent weight of polybutadiene ( )

p = polymer sample when weighed (g)

Example 1

Obtaining the composition using a continuous method in mass

90 parts of ethylbenzene and 910 parts of styrene were fed into a stirred reactor to give a total of 1000 parts. The reaction was carried out at 125°C with an average residence time of 2 hours. After that, the composition of the fluid from the outlet was fed into the second reactor, where the reaction was completed at 135°C with an average residence time of 2 hours.

The reactive polymer composition at a conversion of 72% was heated to 240°C, and then served in a diverter to remove the solvent and residual monomer.

The resulting composition was characterized by a glass transition temperature of 101° C., a melt flow index (MFI 200° C., 5 kg) of 5 g/10 min, a MW molecular weight of 210,000 g/mol, and an MW/Mn ratio of 2.2, where MW is the weight average molecular weight and Mn is the number average molecular weight. Vinyl aromatic composition was fed into the heat exchanger to reduce its temperature to 200°C (component (a) according to the invention).

The extruder was fed with 200 parts of high impact polystyrene (HIPS, very high impact polystyrene) containing 7% polybutadiene as determined by iodometry (commercially available, Edistir® 850E, Versalis spa) as the vinyl aromatic copolymer (c). A gear pump increased the feed pressure of the plasticized HIPS material to 260 bar absolute pressure: after that, 60 parts of a mixture of n-pentane (70%) and isopentane (30%) - expanding agent (b) - and 750 parts of a vinyl aromatic composition (a) from a heat exchanger were added. The ingredients were then mixed using static mixing elements for an average calculated residence time of 7 minutes.

The final composition contained 20% wt. copolymer (c) containing 7% polybutadiene, 6% wt. a mixture of n-pentane (70%) and isopentane (30%) (component (b)) and 74% wt. polystyrene (component (a)). Therefore, the amount of polybutadiene corresponded to 1.4% wt. from the total composition.

The composition was then directed onto a die plate where it was extruded through several 0.6 mm holes, immediately cooled with a water jet, and cut using a rotating knife sequence (as described in US 2005/0123638). The granulation pressure was 500 kPa absolute pressure, and the shear rate was chosen so as to obtain granules having an average diameter of 1.1 mm. Water was used as the spray liquid, and nitrogen was used as the gaseous carrier. The water temperature was 45°C.

The resulting granulated beads were dried using a spin dryer and then coated. The coating was obtained by adding 1 part glyceryl monostearate, 1 part glyceryl tristearate. 1 part zinc stearate per 1000 parts dried granulated grains. The coating additives were mixed into the granulate using a continuous screw mixer. The size of the expandable granules subjected to the expansion process, understood as the weighted average diameter, ranged between 0.9 and 1.2 mm.

The product was pre-expanded in a discrete pre-expander manufactured by AMD, model P125 D (usable volume: 125 liters) using steam at 100°C. The vapor pressure used to pre-expand the polymer beads was set to 1.1 bar absolute pressure (110 kPa). The amount of expandable granules fed into the pre-expander was 1000 g. The expanded grains were left to mature for 12 hours and then used to form blocks (size 1040x1030x550 mm).

Some of the sheets obtained from the block of expanded material were placed in an oven at 70° C. for 3 days (less than 0.15% residual pentane), after which samples were obtained for bending, compression, damping and thermal conductivity tests.

The thermal conductivity at 15.8 g/l measured according to ISO 8301 (1991) was 36.7 mW/m-K.

The bending force measured at 30 mm (5% strain) according to ISO 1209-2 was 209 kPa (sample size 350 x 100 x 25 mm).

The compression stress at 10% according to ISO 844 (2007) was 110 kPa at 17.4 g/l (sample size = 50x50x50 mm).

The density of the expanded layers was 18.0 g/l, and the sintering was 90% (number of broken grains per 100 grains studied).

Damping tests were carried out in accordance with ISO 4651 (1988). In FIG. 1 shows the maximum deceleration values expressed as multiples of the acceleration due to gravity (g in m/s ² ) as a function of the applied force in kPa.

This composition was characterized by an excellent balance of mechanical properties (in terms of both bending and compression, as well as damping), sintering and thermal insulation.

Example 2

Obtaining the composition using a continuous method in mass

Example 1 was repeated using 25% copolymer (c).

The final composition contained 25% wt. copolymer (c), 7% polybutadiene, 5% wt. a mixture of n-pentane (70%) and isopentane (30%) (component (b)) and 70% wt. polystyrene (component (a)). Therefore, the amount of polybutadiene corresponded to 1.75% wt. from the total composition.

The thermal conductivity was 38 mW/m-K at 16.50 g/l. The compression stress at 10% was 100 kPa. The bending force measured at 30 mm (5% deformation) was 204 kPa. The density of the expanded sheets was 18.0 g/l and the sintering was 80%.

Example 3

Obtaining the composition using a continuous method in mass

Example 1 was repeated using 15% copolymer (c).

The final composition contained 15% wt. copolymer (c), 7% polybutadiene, 6% wt. a mixture of n-pentane (70%) and isopentane (30%) (component (b)) and 79% wt. polystyrene (component (a)). Therefore, the amount of polybutadiene corresponded to 1.05% wt. from the total composition.

The thermal conductivity was 36 mW/m-K at 16.40 g/l. The compression stress at 10% was 110 kPa.

The bending force measured at 30 mm (5% deformation) was 215 kPa. The density of the expanded sheets was 18.2 g/l and the sintering was 85%.

Example 4

Obtaining the composition using a continuous method in mass

Example 1 was repeated using another copolymer (c), i.e. high impact polystyrene containing 8.5% polybutadiene (PB) as determined iodometrically (commercially available, Edistir® ICE R830D, Versalis spa).

At the end of the process described in Example 1, a composition was obtained having the same percentage levels, but the copolymer c) used in this example had a higher polybutadiene percentage of 8.5% instead of 7%. Therefore, the amount of polybutadiene was 1.7% wt. from the total composition.

The thermal conductivity was 34.8 mW/m-K at 16.5 g/L. The bending force measured at 30 mm (5% deformation) was 198 kPa. The compression stress at 10% was 99.5 kPa. The density of the expanded sheets was 18.3 g/l and the sintering was 85%.

Example 5

Obtaining the composition using a continuous method in mass

Example 1 was repeated using high impact polystyrene containing 7.5% PB as determined iodometrically (commercially available, Edistir® RC600, Versalis spa). In this case, the amount of component (b) was 4.7%.

At the end of the process described in Example 1, a composition was obtained having the same percentage levels of copolymer (c), but copolymer c) used in this example had a higher polybutadiene percentage of 7.5% instead of 7%. Therefore, the amount of polybutadiene was 1.5% wt. from the total composition.

The thermal conductivity was 35 mW/m-K at 15.60 g/l. The bending force measured at 30 mm (5% deformation) was 191 kPa. The compression stress at 10% was 90 kPa. The density of the expanded sheets was 18.0 g/l and the sintering was 80%. Damping tests are shown in Fig. 1.

Example 6

Getting the composition using the suspension method

A mixture of 150 parts by weight of water, 0.2 parts of sodium pyrophosphate, 80 parts of styrene, 0.25 parts of tert-butylperoxy-2-ethylhexanoate, 0.25 parts of tert-butylperbenzoate and 20 parts of the copolymer (c) used in Example 1 was charged to a sealed stirred container. This charge was heated to 90°C with stirring. After approximately 2 hours at 90° C., 4 parts of a 10% polyvinylpyrrolidone solution were added. With constant stirring, the mixture was heated for another 2 hours at 100°C; added 7 parts of a mixture of n-pentane and isopentane with a composition of 70/30, the resulting was heated for another 4 hours at 125°C, then cooled and unloaded. The expanded polymer pellets thus produced contained 20% copolymer (c) containing 7% polybutadiene, 6% mixture of n-pentane (70%) and isopentane (30%) (component b) and 74% polystyrene (component a).

After that, the pellets were removed and washed with demineralized water containing 0.05% non-ionic surfactant consisting of a fatty alcohol condensed with ethylene oxide and propylene oxide and sold by the company Huntsman under the trade name Empilan 2638. Following this, the pellets were dried in a lukewarm air stream, 0.02% non-ionic surfactant consisting of ethylene oxide condensate was added. and propylene oxide based on glycerol and sold by the Dow company (Voranol CP4755), and then the granules were sieved by separating a fraction having a diameter in the range between 0.9 and 1.2 mm.

This fraction was 50%, with 20% being a fraction in the range between 0.4 and 0.9 mm, 5% being a fraction in the range between 0.2 and 0.4 mm, and 25% being a coarse fraction in the range between 1.5 and 3 mm.

The same coating as in Example 1 was then added to a fraction between 0.9 and 1.2 mm. The resulting product was pre-expanded, molded and characterized in the same manner as in Example 1. The thermal conductivity was 37.5 mW/m-K at 15.9 g/L. The bending force, always measured at 30 mm (5% deformation), was 205 kPa. The compression stress, again at 10%, was 100 kPa. The density of the expanded layers was 18.3 g/l, and the sintering was 80%.

As can be seen, both the mechanical properties and the conductivity were comparable to those of Example 1, but the suitable fraction (0.9-1.2 mm) was only 50%. The yield was only 50%, with the remainder being waste.

Example 7 (comparison example)

Preparation of Comparative Composition Containing 94% Polymer (c)

940 parts of the vinyl aromatic composition of the product Edistir® R850 E (used in Example 1 above), originating from the polymerization section, were placed in a heated vessel and fed into a heat exchanger to reduce its temperature to 200°C.

The gear pump increased the pressure while supplying the plasticized HIPS material to 260 bar: after that, as in example 1, 60 parts of a mixture of n-pentane (70%) and isopentane (30%) were added.

Following this, the composition was mixed using static mixing elements for a calculated average residence time of 7 minutes. Thereafter, the composition was distributed in a system where it was extruded through several holes having a diameter of 0.6 mm, immediately cooled with a jet of water, and cut using a series of rotating knives in the same manner as in example 1.

Thus, the amount of polybutadiene corresponded to 6.58% wt. from the total composition, since polymer (c) was the only component of the composition.

The product was pre-expanded, molded and characterized in the same manner as in Example 1.

The thermal conductivity was 39 mW/m-K at 16 g/l. The bending force was always 180 kPa measured at 30 mm (5% deformation).

The compression stress, again at 10%, was 70 kPa. The density of the expanded layers was 18.1 g/l, and the sintering was 60%. Damping tests are shown in Fig. 1.

Example 8

Obtaining the composition using a continuous method in mass

Example 5 was repeated using 9% copolymer (c) or Edistir®RC600 product. The final composition contained 9% wt. copolymer c) containing 7.5% polybutadiene, 5% wt. pentane (component b)) in the form of a mixture of n-pentane (70%) and isopentane (30%) and 86% wt. polystyrene (component (a)). Therefore, the amount of polybutadiene was 0.675% wt. from the total composition.

The thermal conductivity was 34.1 mW/m-K at 18.1 g/l. The bending force measured at 30 mm (5% deformation) was 234 kPa. The compression stress, again at 10%, was 112 kPa. The density of the expanded layers was 18.0 g/l, and the sintering was 75%. Damping tests are shown in Fig. 1.

Example 9 (comparison example)

Obtaining the composition using a continuous method in mass

90 parts of ethylbenzene and 910 parts of styrene were fed into a stirred reactor to give a total of 1000 parts. The reaction was carried out at 125°C with an average residence time of 2 hours. After that, the composition of the fluid from the outlet was fed into the second reactor, where the reaction was completed at 135°C with an average residence time of 2 hours.

The reactive polymer composition at a conversion of 72% was heated to 240° C. and then fed into a devolatizer to remove the solvent and residual monomer.

The resulting composition had a glass transition temperature of 101° C., a melt flow index (MFI 200° C., 5 kg) of 5.3 g/10 min, an MW molecular weight of 208,000 g/mol, and an MW/Mn ratio of 2.2, where MW is the weight average molecular weight and Mn is the number average molecular weight. Vinyl aromatic composition was fed into the heat exchanger to reduce its temperature to 200°C (component (a) according to the invention). The gear pump increased the pressure of the supplied component (a); then, as in Example 1, 60 parts of a mixture (component (b)) of n-pentane (70%) and isopentane (30%) were added. The ingredients were then mixed using static mixing elements for an average calculated residence time of 7 minutes. The final composition contained 6% wt. a mixture of pentane (component (b)) and 94% wt. polystyrene (component (a)). Thus, the amount of polybutadiene corresponded to 0% wt. from the total composition.

The product was pre-expanded, molded and characterized in the same manner as in Example 1.

The thermal conductivity was 38.6 mW/m-K at 17.2 g/l. In the bending stress test, the sample did not reach 30 mm (corresponding to 5% strain), but broke earlier at 20.7 mm. The compression stress, again at 10%, was 75 kPa. The density of the expanded layers was 18.2 g/l, and the sintering was 25%.

Analysis of FIG. 1

As can be seen from FIG. 1, the damping curves for Example 1 and Example 8 are almost identical to the corresponding curve from Comparative Example 7, despite the different level of rubber content in the total composition (1.4% in Example 1 and 0.675% in Example 8 compared to 6.58% in Comparative Example 7). It should not be forgotten that the damping property of a package expresses its ability to absorb impact energy depending on the applied static stress (force per unit surface area). This capability is measured using an impact factor expressed in multiples of the earth's acceleration g and represents the deceleration due to the absorption of impact energy by the product.

The sintering values for examples 1, 2, 3, 4, 5, 6 and 8 are greater than the corresponding values for comparative examples 7 (6.58% rubber component) and 9 (0% rubber component).

The thermal conductivity values for examples 1, 2, 3, 4, 5, 6 and 8 are greater than the corresponding values for comparative examples 7 (6.58% rubber component) and 9 (0% rubber component).

The bending behavior for examples 1, 2, 3, 4, 5, 6, 7 and 8 is better than the corresponding behavior for example 9 (0% rubber component).

The compression behavior for examples 1, 2, 3, 4, 5, 6 and 8 is better than the corresponding behavior for comparative examples 7 (6.58% rubber component) and 9 (0% rubber component).

Claims (48)

1. Expandable vinyl aromatic polymer composition containing: a) from 60% to 96% wt. vinyl aromatic polymer (a); b) from 3% to 10% wt. expanding agent (b); c) from 1% to 30% wt. vinylaromatic copolymer (c), containing from 1% to 10% wt. a rubber component as a dispersed phase; provided that the sum of (a), (b) and (c) is 100% wt. 2. The composition according to p. 1, where the vinyl aromatic polymer (a) is a polymer obtained from at least 65% wt. vinyl aromatic monomer. 3. The composition according to any one of paragraphs. 1, 2, where the vinyl aromatic monomers used to obtain the vinyl aromatic polymer (a) are described by the general formula (I): wherein R represents a hydrogen atom or a methyl group; n is zero or an integer in the range 1 to 3; Y is selected from a halogen atom, preferably chlorine or bromine atoms, chloromethyl, an alkyl group or an alkoxy group containing from 1 to 3 carbon atoms. 4. Composition according to claim 3, wherein the vinyl aromatic monomers of formula (I) are selected from styrene, α-methylstyrene, methylstyrene, ethylstyrene, vinyltoluene isomers, ethylstyrene isomers, propylstyrene isomers, chlorostyrene isomers, methylchlorostyrene isomers, methoxystyrene isomers, acetoxystyrene isomers, hydroxystyrene ionic isomers, methylhydroxystyrene isomers and mixtures thereof. 5. The composition according to p. 3, where vinylaromatic monomers of General formula (I) can be used individually, in a mixture or in a mixture containing up to 35% wt. other copolymerizable vinyl monomers selected from (meth)acrylic acid, maleic anhydride, (meth)acrylic acid alkyl esters containing from 1 to 18 carbon atoms, amides and (meth)acrylic acid nitriles. 6. The composition of claim 4 wherein the vinyl aromatic monomer is styrene. 7. The composition of claim 4 wherein styrene makes up at least 85% of the mixture of vinyl aromatic monomers used to produce the vinyl aromatic polymer (a). 8. The composition according to claim 1, where the vinyl aromatic copolymer (c) is a copolymer obtained from at least one vinyl aromatic monomer according to claim 3, containing as a dispersed phase a rubber component selected from polybutadiene, polyisoprene, copolymers of butadiene and / or isoprene with styrene or other vinyl monomers. 9. The composition according to claim 1, where the vinyl aromatic copolymer (c) is present in an amount of from 9 to 25% wt., and where the rubber component dispersed in the vinyl aromatic copolymer (c) may be in the range between 3 and 9% wt. 10. The composition according to claim 1, wherein the rubber component dispersed in the vinyl aromatic copolymer (C) is polybutadiene (PB) and/or styrene-diene block copolymers. 11. The composition according to p. 1, where the expanding agent (b) is present in an amount in the range from 4 to 7% wt. 12. The composition according to claim 1, where the expanding agent (b) is selected from aliphatic or cycloaliphatic hydrocarbons containing from 3 to 6 carbon atoms, such as n-pentane, isopentane, cyclopentane, butane, isobutane and mixtures thereof; or halogenated derivatives of aliphatic hydrocarbons containing from 1 to 3 carbon atoms, such as dichlorodifluoromethane, 1,2,2-trifluoroethane and 1,1,2-trifluoroethane; or carbon dioxide. 13. Composition according to claim 1, containing: a) from 67% to 88% wt. vinyl aromatic polymer (a); b) from 3% to 8% wt. expanding agent (b); c) from 9% to 25% wt. a vinyl aromatic copolymer (c) containing 2% to 10% rubber component as a dispersed phase; provided that the sum of (a), (b) and (c) is 100% wt. 14. Composition according to claim 1, containing: a) from 69% to 83% wt. vinyl aromatic polymer (a); b) from 4% to 7% wt. expanding agent (b); c) from 13% to 24% wt. a vinyl aromatic copolymer (c) containing 3% to 9% of a rubber component as a dispersed phase; provided that the sum of (a), (b) and (c) is 100% wt. 15. Composition according to claim 1, consisting of: a) from 69% to 81% wt. polystyrene; b) from 4% to 6% wt. expanding agent (b); c) from 15% to 25% wt. copolymer formed from high-impact polystyrene containing from 4% to 9% wt. polybutadiene; provided that the sum of (a), (b) and (c) is 100% wt. 16. Composition according to claim 1, consisting of: a) from 72% to 79% wt. polystyrene; b) from 4% to 6% wt. expanding agent (b); c) from 17% to 22% wt. copolymer obtained from high-impact polystyrene containing from 7% to 8.5% wt. polybutadiene; provided that the sum of (a), (b) and (c) is 100% wt. 17. Continuous method in mass to obtain compositions according to paragraphs. 1-16, which includes the following steps in this order: i. mixing vinyl aromatic polymer (a) and vinyl aromatic copolymer (c) in the form of granules, powder or pre-melted, ii. optionally, if melting has not yet occurred, bringing the polymer mixture to a temperature higher than or equal to the melting point of the vinyl aromatic polymer (a) and copolymer (c); iii. including at least one expanding agent (b) in the molten polymer mixture forming the vinyl aromatic polymer composition of claim 1; iv. mixing the polymer composition thus obtained using static or dynamic mixing elements; v. sending the polymer composition obtained after mixing to the matrix plate with cutting under pressure. 18. Expanded product containing the composition according to any one of paragraphs. 1-16.

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