WO2020099304A1

WO2020099304A1 - Foamed composition

Info

Publication number: WO2020099304A1
Application number: PCT/EP2019/080837
Authority: WO
Inventors: Armand Alphons Marie Agnes DUIJSENS
Original assignee: DSM IP Assets BV
Current assignee: DSM IP Assets BV
Priority date: 2018-11-13
Filing date: 2019-11-11
Publication date: 2020-05-22
Anticipated expiration: 2021-05-13
Also published as: CN112969745B; KR20210093289A; CN112969745A

Abstract

The invention relates to a process for preparing a foamed composition comprising at least the following steps a, b, c and d: • a. Providing a composition comprising a thermoplastic copolyester elastomer comprising hard segments and soft segments; • b. Bringing the composition to a temperature of between (Tm - 100°C) and Tm, in which Tm is the melting temperature of the hard segment of the thermoplastic copolyester elastomer as measured according to ISO 11357-1:1997 by DSC in the second heating curve, with a heating and cooling rate of 10°C per min, under nitrogen atmosphere; and providing a physical blowing agent under pressure to the composition; • c. lowering the pressure in at least 3 phases: • i. In a first phase, with a pressure decrease of between 10 and 100 bar, during a time interval between 0.1 sec and 3 sec; • ii. In a second phase which is after the first phase, with a pressure decrease of between 10 and 600 bar, with respect to the pressure obtained after phase i, during a time interval between 1 sec and 100 sec; • iii. In a third phase which is after the second phase, lowering the pressure as obtained after phase ii, during a time interval of at least 10 sec; • d. Allowing the composition to cool, thereby obtaining the foamed composition.

Description

FOAMED COMPOSITION

This invention relates to a process for preparing a foamed

composition, a foamed composition and an article comprising the foamed composition.

Foamed compositions are known and are for example described in EP0610953A1. A disadvantage of these foams is that they may show cracks, especially when low density foams are required. Without wishing to be bound by theory the inventors believe that cracks are formed by overstretching of cell walls, causing rupture and cascading failure of cells leading to formation of a big bubble. After foaming, a bubble is usually visible, which disappears over time, and leaving a so- called crack. W015177571 A1 describes a process in which foamed compositions can be prepared with various shapes. A disadvantage however, is that the foams cannot be recycled. Providing foamed compositions with a low amount of cracks and sufficiently low density and being able to recycle these compositions, is very important in view of consumer requirements and environmental reasons.

It is thus an object of the present invention to provide a process for foamed composition which exhibits less cracks while having a sufficiently low density and being able to recycle after use. This object is achieved by a process for preparing a foamed composition comprising at least the following steps a, b, c and d:

a. Providing a composition comprising a thermoplastic copolyester elastomer comprising hard segments and soft segments;

b. Bringing the composition to a temperature of between (Tm-100) °C and Tm, in which Tm is the melting temperature of the hard segment of the thermoplastic copolyester elastomer as measured according to ISO 1 1357- 1 :1997 by DSC in the second heating curve, with a heating and cooling rate of 10 °C per min, under nitrogen atmosphere; and providing a physical blowing agent under pressure to the composition;

c. lowering the pressure in at least 3 phases:

i. In a first phase, with a pressure decrease of between 10 and 100 bar, during a time interval between 0.1 sec and 3 sec;

ii. In a second phase which is after the first phase, with a pressure

decrease of between 10 and 600 bar, with respect to the pressure obtained after phase i, during a time interval between 1 sec and 100 sec; iii. In a third phase which is after the second phase, lowering the pressure as obtained after phase ii, during a time interval of at least 10 sec;

d. Allowing the composition to cool, thereby obtaining the foamed

composition.

Surprisingly, the inventors have found that by lowering the pressure in a controlled gradual way, the obtained foam exhibits less cracks while lower densities may be obtained. Lower density crack-free foams are very attractive as it is an important selling argument in applications where light-weight is favorable, for example sports shoes. Cracks may initiate failure in an application when mechanical stress will be applied, which is undesirable.

A foamed composition is herein understood to be known to a person skilled in the art. Preferably a foamed composition has a density of at most 0.7 g/cm³.

Preferably, the process for preparing a foamed composition, comprises at least the following steps a, b, c and d:

a. Providing a composition comprising a thermoplastic copolyester elastomer, wherein the thermoplastic copolyester elastomer comprises hard segments built up from polyester repeating units derived from at least one aliphatic diol and at least one aromatic dicarboxylic acid or an ester thereof, and soft segments chosen from the group consisting of aliphatic polyether, aliphatic polyester, aliphatic polycarbonate, dimer fatty acids and dimer fatty diols and combinations thereof;

b. Bringing the composition to a temperature of between (Tm-100) and Tm, in which Tm is the melting temperature in °C, of the hard segment of the thermoplastic copolyester elastomer as measured according to ISO 1 1357- 1 :1997 DSC in the second heating curve, with a heating and cooling rate of 10 °C per min under nitrogen atmosphere and providing a physical blowing agent under pressure to the composition;

c. Lowering the pressure in at least 3 phases:

ii. In a second phase which is after the first phase, with a pressure

d. Allowing the composition to cool, thereby obtaining the foamed

composition.

Preferably, the composition comprises a thermoplastic copolyester elastomer comprising hard segments and soft segments, in an amount of at least 70 wt%, more preferably at least 75 wt%, and even more preferred at least 80 wt%, in which wt% is based on the total amount of the composition.

The process is particularly suitable for a composition comprising a thermoplastic copolyester elastomer comprising hard segments chosen from PBT or PET and soft segments chosen from the group consisting of polybutylene adipate (PBA), polyethylene oxide) (PEO), polypropylene oxide (PPO), polytetramethylene oxide (PTMO), ), PEO-PPO-PEO and combinations thereof and optionally a plasticizer chosen from group consisting of Triphenyl phosphate (TPP), tert-Butylphenyl diphenyl phosphate (Mono-t-but-TPP), di-tert-butylphenyl phenyl phosphate (bis-t-but-TPP), Tris(p-tert-butylphenyl) phosphate (tri-t-but-TPP), Resorcinol bis (Diphenyl Phosphate) (RDP), dichloropropyl phosphate, Bisphenol A bis-(Diphenyl Phosphate) (BDP), tricresyl phosphate (TCP), triethyl phosphate, tributyl phosphate (TBP), tri-2-ethylhexyl phosphate, trimethyl phosphate, epoxidized soybean oil (ESO), epoxidized palm oil (EPO), epoxidized linseed oil (ELO) and argan oil and combinations thereof.

Tm is herein understood being the melting temperature of the hard segment of the thermoplastic copolyester elastomer as measured according to ISO 11357-1 :1997 by DSC in the second heating curve, with a heating and cooling rate of 10 °C per min, under nitrogen atmosphere.

With“bringing the composition to a temperature” in step b is herein understood to encompass both heating as well as cooling to come to the desired temperature. Usually, heating will be employed. During step b,“bringing the composition to a temperature” and“providing a physical blowing agent” may be done simultaneously, but not necessarily. If first a physical blowing agent is provided then the“bringing the composition to a temperature” has to be applied under pressure to prevent the composition from foaming. During step b, a physical blowing agent under pressure is applied. Usually, the pressure is chosen such that the physical blowing agent is in a supercritical state. Before step b, the composition may be molded into a pre-form, by processes such as molding.

Preferably, during step b, the pressure is maintained such that the physical blowing agent substantially dissolves in the composition.

With physical blowing agent is herein understood to be a substance which may dissolve in the composition, without reacting or decomposing. Physical blowing agent may for example be chosen from hydrocarbons such as pentane, isopentane, cyclopentane, butane, isobutene and CO2 and nitrogen as well as mixtures thereof. Typical pressures for CO2 before starting step c is at least 150 bar, more preferably at least 200 bar. Typical pressures for nitrogen before starting step c is at least 500 bar, more preferably at least 600 bar.

The“bringing the composition to a temperature” in step b is preferably done to a temperature of at most (Tm - 5), more preferably at most (Tm-10), most preferred at most (Tm-15). The“bringing the composition to a temperature” step b is preferably done to a temperature of at least (Tm-80), more preferably at least (Tm-60), most preferred at least (Tm-40), as this provides foams with lower densities. Usually heating is applied by for example an external heat source while keeping the

composition in a pressure vessel.

In each phase of step c, the pressure can be lowered gradually or multi-step wise, for example by going from its initial to a lower value in a rather continuous manner or in more discrete steps.

With“pressure decrease” is herein understood lowering the absolute pressure with a given value. The absolute pressure depends on the particular physical blowing agent used in combination with the applied temperature.

The phases in step c can be carried out in one vessel but may also be performed in different vessels. The three phases may immediately follow each other, but may also contain further phases between the at least three phases as described in step c.

Figure 1 provides an embodiment of lowering the pressure in which the three phases i, ii and iii immediately follow each other. The time interval of each phase is denoted by At,, At,, and At_m respectively and the pressure decrease of each phase is denoted by Ap,, Ap,, and Ap respectively. Figure 2 provides an embodiment of lowering the pressure in which between the three phases time intervals are present in which the pressure remains substantially constant. The time interval of each phase is denoted by At,, At,, and At_m respectively and the pressure decrease of each phase is denoted by Ap,, Apn and Ap_m respectively.

Step c is performed in manner so that the pressure is lowered in at least three phases:

i. In a first phase, with a pressure decrease of between 10 and 100 bar, during a time interval between 0.1 sec and 3 sec; preferably a pressure decrease of between 20 to 80 bar, more preferably between 30 to 70 bar;

ii. In a second phase which is after the first phase, with a pressure decrease of between 10 and 600 bar, with respect to the pressure obtained after phase i, during a time interval between 1 sec and 100 sec, preferably a pressure decrease of between 15 and 400 bar and even more preferred between 25 and 250 bar;

iii. In a third phase which is after the second phase, lowering the pressure as obtained after phase ii, during a time interval of at least 10 sec, preferably the pressure is lowered until atmospheric pressure.

Preferably, in the second phase ii, which is after the first phase, the pressure is decreased during a time interval between 1 sec and 10 sec, as this allows for a faster process.

In step c, besides lowering the pressure, also the temperature of the composition may be varied. Preferably, the temperature is lowered during the phases in step c. In phase i the temperature is preferably between (Tm-100) and Tm. In phase ii, the temperature is preferably 0 to 10 °C lower than the temperature after phase i, more preferably 1 to 10 °C lower. In phase iii, the temperature is preferably 0 to 10 °C lower than the temperature after phase ii. Lowering the pressure may influence the temperature of the composition due to expansion. In the context of the invention, the temperature in step c is the temperature of the external heat or cooling source of the vessel or vessels in which step c is carried out.

In a preferred embodiment, step c is applied in at least three phases: i. In a first step a pressure decrease is applied of between 10 to 100 bar, at a temperature of between (Tm-100) and Tm.

ii. In a second step a pressure decrease is applied of between 10 to 400 bar, at a temperature which is 1 to 10 °C lower than the temperature after phase i iii. In a third step the pressure is released to ambient pressure, at a temperature which is 0 to 10 °C below the temperature after phase ii.

The process to prepare the foamed composition as described above is generally known as a batch foaming or solid-state foaming process and is to be distinguished from extrusion foaming. In a process for extrusion foaming the composition is generally to be heated to above its melting temperature.

Surprisingly, the process resulted in foams exhibiting less cracks, which allowed for very low-density foams.

A thermoplastic copolyester elastomer is herein understood to be a copolymer comprising hard segments built up from polyester repeating units derived from at least one aliphatic diol and at least one aromatic dicarboxylic acid or an ester thereof, and soft segments chosen from the group consisting of aliphatic polyether, aliphatic polyester, aliphatic polycarbonate, dimer fatty acids and dimer fatty diols and combinations thereof. Surprisingly, the method allows for preparing a foaming composition in which a cross-linking step may be omitted.

The thermoplastic copolyester elastomer may contain minor amounts of comonomers, such as branching agents, chain extenders, and catalysts, which are usually employed during preparation of the thermoplastic copolyester elastomer. With minor amounts is herein understood to be at most 10 wt% with respect to the total amount of thermoplastic copolyester elastomer. An example of such comonomer is dimethyl isophthalate (DMI).

Hard segments are built up from polyester repeating units derived from at least one aliphatic diol and at least one aromatic dicarboxylic acid or an ester thereof and optionally minor amounts of other diacids and/or diols.

Aliphatic diols contain generally 2-10 C-atoms, preferably 2-6 C- atoms. Examples thereof include ethylene glycol, 1 ,2-propylene glycol, 1 ,3-propylene glycol, butylene glycol, 1 ,2-hexane diol, 1 ,6-hexamethylene diol, 1 ,4-butanediol, 1 ,4- cyclohexane diol, 1 ,4-cyclohexane dimethanol, and mixtures thereof. Preferably, 1 ,4- butanediol is used.

Suitable aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid and 4,4'- diphenyldicarboxylic acid, and mixtures thereof. Also very suitable is a mixture of 4,4’- diphenyldicarboxylic acid and 2,6-naphthalenedicarboxylic acid or a mixture of 4,4’- diphenyldicarboxylic acid and terephthalic acid. The mixing ratio between 4,4’- diphenyldicarboxylic acid and 2,6-naphthalenedicarboxylic acid or 4,4’- diphenyldicarboxylic acid and terephthalic acid is preferably chosen between 40:60 - 60:40 on weight basis in order to optimize the melting temperature of the thermoplastic copolyester.

The hard segment preferably has as repeating unit chosen from the group consisting of ethylene terephthalate (PET), propylene terephthalate (PPT), butylene terephthalate (PBT), polyethylene bibenzoate, polyethelyene naphatalate, polybutylene bibenzoate, polybutylene naphatalate, polypropylene bibenzoate and polypropylene naphatalate and combinations thereof. Preferably, the hard segment is butylene terephthalate (PBT), as thermoplastic copolyester elastomers comprising hard segments of PBT exhibit favourable crystallisation behaviour and a high melting point, resulting in thermoplastic copolyester elastomer with good processing properties and excellent thermal and chemical resistance.

Soft segments chosen from aliphatic polyesters have repeating units derived from an aliphatic diol, and an aliphatic dicarboxylic acid or repeating units derived from a lactone. Suitable aliphatic diols contain generally 2-20 C-atoms, preferably 3-15 C-atoms in the chain and an aliphatic dicarboxylic acid containing 2 - 20 C atoms, preferably 4 - 15 C atoms. Examples thereof include ethylene glycol, propylene glycol, butylene glycol, 1 ,2-hexane diol, 1 ,6-hexamethylene diol, 1 ,4- butanediol, cyclohexane diol, cyclohexane dimethanol, and mixtures thereof.

Preferably, 1 ,4-butanediol is used. Suitable aliphatic dicarboxylic acids include sebacic acid, 1 ,3-cyclohexane dicarboxylic acid, 1 ,4-cyclohexane dicarboxylic acid, adipic acid, glutaric acid, 2-ethylsuberic acid, cyclopentanedicarboxylic acid, decahydro-1 ,5- naphtylene dicarboxylic acid, 4,4’-bicyclohexyl dicarboxylic acid, deca hydro-2, 6- naphthylene dicarboxylic acid, 4,4’-methylenebis (cyclohexyl)carboxylic acid and 2,5- furan dicarboxylic acid. Preferred acids are sebacic acid, adipic acid, 1 ,3-cyclohexane dicarboxylic acid, 1 ,4-cyclohexane dicarboxylic acid. Most preferred is adipic acid.

Preferably, the soft segment is polybutylene adipate (PBA) which may be obtained from 1 ,4 butanediol and adipic acid.

The soft segment may be aliphatic polyethers, which may comprise units of polyalkylene oxides, such as polyethylene oxide and polypropylene oxide and polytetramethylene oxide and combinations thereof, either as individual segment or combined in one segment. A combination is for example ethylene oxide-capped polypropylene oxide.

A preferred soft segment is polytetramethylene oxide (PTMO). Also soft segments comprising a block copolymer in which two types of glycols are reacted to form a soft segment such as based on poly(ethylene oxide) (PEO) and

polypropylene oxide (PPO). The latter is also referred to as PEO-PPO-PEO, as the PEO blocks are at the ends of a soft segment as PEO reacts best with a hard segment. PTMO, PPO and PEO based soft segments allow for foams having a lower density.

The soft segment may be an aliphatic polycarbonate which is preferably made up of repeating units from at least one alkylene carbonate.

Preferably as alkylene carbonate repeating unit is represented by the formula:

O

II

-0-(Ri)_x-0-C- (form. 1 ) where Ri= alkyl.

X= 2 - 20.

Preferably Ri = CH2 and x = 6 and the alkylene carbonate is therefore hexamethylene carbonate, as this provides high heat resistance to the article and is readily available.

The soft segment may be a dimer fatty acids or dimer fatty diols and combinations thereof. The dimerised fatty acids may contain from 32 up to 44 carbon atoms. Preferably the dimerised fatty acids contain 36 carbon atoms. Also suitable are dimer fatty diols which may be derived from the dimer fatty acids as disclosed above. For example a dimerised fatty diol may be obtained as a derivative of the dimerised fatty acid by hydrogenation of the carboxylic acid groups of the dimerised fatty acid, or of an ester group made thereof. Further derivatives may be obtained by converting the carboxylic acid groups, or the ester groups made thereof, into an amide group, a nitril group, an amine group or an isocyanate group.

In a preferred embodiment the foamed composition comprising a thermoplastic copolyester elastomer having hard and soft segments, wherein the hard segment is chosen from PBT or PET and the soft segment is chosen from the group consisting of polybutylene adipate (PBA) polyethylene oxide) (PEO), polypropylene oxide (PPO), polytetramethylene oxide (PTMO), PEO-PPO-PEO and combinations thereof, as this provided an article exhibiting low densities.

Preferably, the composition comprises plasticizer. Plasticizers are known substances to a person skilled in the art per se, and for example lowers the hardness and/or increases the strain at break of the composition as compared to the elastomer itself. Plasticizers may optionally be present in an amount of between 1 to 30 wt% based on the total amount of the composition, preferably between 5 to 25 wt% and even more preferred between 8 to 20 wt%.

Plasticizers include for example phthalate esters, dibasic acid esters, mellitates and esters thereof, cyclohexanoate esters, citrate esters, phosphate esters, modified vegetable oil esters, benzonate esters, and petroleum oils, and combinations thereof.

Examples of phthalate esters include dioctyl phthalate, dibutyl phthalate, diethyl phthalate, butylbenzyl phthalate, di-2-ethylhexyl phthalate, diisodecyl phthalate, diundecyl phthalate, diisononyl phthalate, diethyl hexyl terephthalate (DEHT), dioctyl terephthalate, dibutyl terephathalate.

Examples of dibasic acid esters include di-2-ethylhexyl adipate (DEHA), dioctyl adipate, diisobutyl adipate, dibutyl adipate, diisodecyl adipate, dibutyl glycol adipate, di-2-ethylhexyl azelate and dioctyl sebacate.

Examples of mellitates and esters thereof include trioctyl trimellitate, trimellitic acid tri-2-ethylhexyl and pyromellitic acid octyl ester.

Examples of cyclohexanoate esters include cyclohexanedicarboxylic acid ester, 2-ethyl hexanol cyclohexanedicarboxylic acid ester.

Example of phosphate esters include Triphenyl phosphate (TPP), tert-Butylphenyl diphenyl phosphate (Mono-t-but-TPP), di-tert-butylphenyl phenyl phosphate (bis-t-but-TPP), Tris(p-tert-butylphenyl) phosphate (tri-t-but-TPP),

Resorcinol bis (Diphenyl Phosphate) (RDP), dichloropropyl phosphate, Bisphenol A bis-(Diphenyl Phosphate) (BDP), tricresyl phosphate (TCP), triethyl phosphate, tributyl phosphate (TBP), tri-2-ethylhexyl phosphate, trimethyl phosphate and combinations thereof. A blend of TPP, mono-t-But-TPP, Bis-t-But-TPP, Tri-t-But-TPP is also known under the name Phosflex 71 B HP and is particularly suitable, as it is easily mixed with the thermoplastic elastomer.

Examples of modified vegetable oil esters include epoxidized soybean oil (ESO), epoxidized palm oil (EPO), epoxidized linseed oil (ELO) and Argan oil.

Preferably, phosphate esters and modified vegetable oil esters are being employed, as these are commonly used plasticizers and easily processable.

In a particular preferred embodiment the composition comprises a thermoplastic copolyester elastomer in an amount of between 70 to 99 wt% and a plasticizer in an amount of between 1 to 30 wt% based on the total amount of the composition wherein thermoplastic copolyester elastomer comprises hard and soft segments wherein the hard segment is chosen from PBT or PET and the soft segment is chosen from the group consisting of polybutylene adipate (PBA), poly(ethylene oxide) (PEO), polypropylene oxide (PPO) and polytetramethylene oxide (PTMO) and combinations thereof and the plasticizer is chosen from the group consisting of

Triphenyl phosphate (TPP), tert-Butylphenyl diphenyl phosphate (Mono-t-but-TPP), di- tert-butylphenyl phenyl phosphate (bis-t-but-TPP), Tris(p-tert-butylphenyl) phosphate (tri-t-but-TPP), Resorcinol bis (Diphenyl Phosphate) (RDP), dichloropropyl phosphate, Bisphenol A bis-(Diphenyl Phosphate) (BDP), tricresyl phosphate (TCP), triethyl phosphate, tributyl phosphate (TBP), tri-2-ethyl hexyl phosphate, trimethyl phosphate, epoxidized soybean oil (ESO), epoxidized palm oil (EPO), epoxidized linseed oil (ELO) and argan oil and combinations thereof. In an even more preferred embodiment, the plasticizer is chosen from the group consisting of ESO, ELO, Phosflex 71 B HP (a blend of TPP, mono-t-But-TPP, Bis-t-But-TPP, Tri-t-But-TPP), RDP, BDP, TCP and TPP, and combinations thereof, as these plasticizers are readily available.

The composition may optionally comprise other ingredients such as colorants, pigments, nucleating agents, flame retardants, UV-stabilizers, heat- stabilizers.

The process is very suitable for preparing foamed composition for application in articles for sport goods, such as shoe soles, preferably inner shoe soles or midsoles, seatings, matrasses, golf balls, foamed tapes, load bearing and cushioning applications, as the article shows a combination of low density and a high energy return and can be recycled at the end of its lifetime. The invention thus also relates to an article comprising the foamed composition as disclosed above.

Surprisingly the foamed composition has a density of preferably between 0.05 to 0.7 g/cm³, more preferably between 0.06 to 0.3 g/cm³ , even more preferred between 0.1 to 0.3 g/cm³ and even more preferred between 0.1 and 0.2 g/cm³ and most preferred between 0.08 and 0.2 g/cm³. Particularly when the soft segment is chosen from the group consisting of poly(ethylene oxide) (PEO), polypropylene oxide (PPO) and polytetramethylene oxide (PTMO), PEO-PPO-PEO, and combinations thereof, low densities could be obtained. Examples

Materials used

Elastomer A: A copolyether-ester elastomer comprising 55wt% polytetramethylene oxide soft segment and poly butylene terephthalate (PBT) hard segment, having a shore D hardness of 33 (ISO 868) and MFI of 33 cm³/10min at 2.16 kg load at 230°C (ISO 1133) and a melting temperature of the hard segment in the thermoplastic copolyester elastomer being 161.5°C as measured with DSC according to ISO 1 1357-1 :1997 in the second heating curve, with a heating and cooling rate of 10 °C per min, under nitrogen atmosphere.

ESO: epoxidized soybean oil

Phosflex: Phosflex 71 B HP, which is a blend of TPP, mono-t-But-TPP, Bis-t-But-TPP, Tri-t-But-TPP.

Sample preparation

The compositions for foaming were prepared by compounding Elastomer A with varying plasticizer types and amounts as listed in Table 1. The melting temperature listed in Table 1 is the peak melting temperature of the hard segment in the thermoplastic copolyester elastomer composition during second heating cycle in a DSC at heating and cooling rates of 10 °C/min under nitrogen atmosphere. Subsequently, plates were injection molded with lateral dimensions of 80^*80 mm and different thicknesses as listed in T able 1. Samples with lateral dimensions of 15^*15 mm were cut out of these plates for foaming tests.

Comparative experiment A and B were foamed as follows:

The sample with lateral dimensions of 15^*15 mm and thickness as listed in Table 1 was placed in a pressure vessel that was electrically heated to the foaming temperature listed in Table 1.

Subsequently, cavity was filled with CO2 at the pressure listed in Table 1 by a CO2 canister connected to the pressure vessel via a booster pump The composition was allowed to absorb CO2 for the soaking time listed in Table 1

The pressure vessel was opened, thus achieving a fast pressure drop resulting in the foamed composition. Pressure was released from 200 bar to atmospheric in 0.5 seconds. Samples were visually inspected within one minute after opening the pressure vessel for bubbles on the surface, indicating the presence of cracks in the interior of the sample. Examples of samples showing indications of cracks are depicted in Figure 1 right column. The left column of Figure 1 shows a sample containing no cracks.

Volume of the sample was determined by measuring length, width, and thickness using a vernier gauge after 24 hours after foaming to allow the CO2 still present in the sample to diffuse out. Mass of the sample was determined by weighing and density of the sample was determined by dividing mass by volume.

Both comparative experiment A and B were foamed at the highest possible foaming temperature to attain lowest possible density without observing cracks. Foaming temperature could be decreased to 115 °C, however, this led to higher densities. If the foaming temperature was further increased, thus above 125 °C, it was no longer possible to avoid cracking.

Examples 1 and 2 are foamed with the same compositions as compared to comparative experiment A and B, respectively. For examples 1 and 2, samples with lateral dimensions of 15^*15 mm and thickness as listed in Table 1 are placed in a pressure vessel that is electrically heated to a foaming temperature of 125 °C. Subsequently, cavity is filled with C02 at the pressure listed in Table 1 by a C02 canister connected to the pressure vessel via a booster pump. The composition is allowed to absorb C02 for the soaking time listed in Table 1.Therafter, the pressure is lowered in a first phase from 200 bar to 120 bar, during a time interval of 1 sec. In a second phase, the pressure is decreased from 120 bar to 40 bar, during a time interval of 80 sec. In a third phase, the pressure is lowered to atmospheric pressure during a time interval of 250 sec after which the pressure vessel is opened. The temperature of the external heat source in the first phase is set to 125 °C; in the second phase the temperature of the external heat source is set to 120 °C and in the third phase the temperature of the external heat source is set to 1 15 °C. After the third phase, the composition is allowed to cool. Samples are visually inspected within one minute after opening the pressure vessel for bubbles on the surface, indicating the presence of cracks in the interior of the sample. Examples of samples showing indications of cracks are depicted in Figure 1 right column. The left column of Figure 1 shows a sample containing no cracks. Volume of the sample is determined by measuring length, width, and thickness using a vernier gauge after 24 hours after foaming to allow the CO2 still present in the sample to diffuse out. Mass of the sample is determined by weighing and density of the sample is determined by dividing mass by volume.

Table 1

The foam of example 1 exhibits a density lower than the density of comparative experiment A, and no cracks are observed. The foam of example 2 exhibits a density lower than the density of comparative experiment B, and no cracks are observed. Surprisingly, by lowering the pressure in at least 3 phases, it is possible to achieve lower densities without formation of cracks.

Claims

1 . Process for preparing a foamed composition comprising at least the following steps a, b, c and d:

a. Providing a composition comprising a thermoplastic copolyester

elastomer comprising hard segments and soft segments; b. Bringing the composition to a temperature of between (Tm-100) °C and Tm, in which Tm is the melting temperature of the hard segment of the thermoplastic copolyester elastomer as measured according to ISO 11357-1 :1997 by DSC in the second heating curve, with a heating and cooling rate of 10 °C per min, under nitrogen atmosphere; and providing a physical blowing agent under pressure to the composition;

c. lowering the pressure in at least 3 phases:

ii. In a second phase which is after the first phase, with a pressure decrease of between 10 and 600 bar, with respect to the pressure obtained after phase i, during a time interval between 1 sec and 100 sec;

iii. In a third phase which is after the second phase, lowering the pressure as obtained after phase ii, during a time interval of at least 10 sec;

d. Allowing the composition to cool, thereby obtaining the foamed

composition.

2. Process according to claim 1 , wherein in step c the at least 3 phases are:

i. In a first phase, with the pressure decrease of between 10 and 100 bar, during a time interval between 0.1 sec and 3 sec, and at a temperature between (Tm-100) and Tm;

ii. In a second phase which is after the first phase, with the pressure decrease of between 10 and 600 bar, with respect to the pressure obtained after phase i, during a time interval between 1 sec and

100 sec, at a temperature which is 0 to 10 °C lower than the temperature after phase i;

iii. In a third phase which is after the second phase, lowering the pressure as obtained after phase ii, during a time interval of at least 10 sec, at a temperature which is 0 to 10 °C below the temperature after phase ii.

3. Process according to claim 1 or 2, wherein the composition comprises a

thermoplastic copolyester elastomer comprising hard segments built up from polyester repeating units derived from at least one aliphatic diol and at least one aromatic dicarboxylic acid or an ester thereof, and soft segments chosen from the group consisting of aliphatic polyether, aliphatic polyester, aliphatic polycarbonate, dimer fatty acids and dimer fatty diols and combinations thereof.

4. Process according to claim 1 or 2, wherein the composition comprises a

thermoplastic copolyester elastomer comprising hard segments chosen from PBT or PET and soft segments chosen from the group consisting of polybutylene adipate (PBA), polyethylene oxide) (PEO), polypropylene oxide (PPO), polytetramethylene oxide (PTMO), ), PEO-PPO-PEO and

combinations thereof.

5. Process according to any one of the prededing claims, wherein the

composition comprises a thermoplastic copolyester elastomer comprising hard segments being PBT.

6. Process according to any one of the preceding claims, wherein the

composition comprises at least 70 wt% of the thermoplastic copolyester elastomer comprising hard segments and soft segments, wherein wt% is with respect to the total amount of composition.

7. Process according to any one of the preceding claims, wherein the

composition further comprises a plasticizer.

8. Process according to claim 7, wherein the amount of plasticizer is between 1 and 30 wt% based on the total amount of the composition.

9. Foamed composition obtainable by the process according to any one of the proceeding claims, wherein the density of the foam is between 0.05 to 0.7 g/cm³.

10. Article comprising the foamed composition according to claim 9.

1 1 . Article according to claim 10, being a shoe sole, preferably inner shoe sole and/or or midsole, a seating, a matrass, a golf ball, or a foamed tape.