AU652512B2 - Process for producing polyester resin foam - Google Patents

Description

p- i~ _-i._ltLI .I ~lil.--iii_ i I _J i ih S F Ref: 227528

AUSTRALIA

PATENTS ACT 1990 6520 1 COMPLETE SPECIFCA1TON FOR A STANDARD PATENT

ORIGINAL

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rrra rr r Iri i rt Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Sekisui Kaseihin Kogyo Kabushiki Kaisha No. 25, Minami Kyobate-cho 1-chome Nara-shi Nara

JAPAN

Motoshige Hayashi, Norio Amano, Takeshi Hirai Taki, Takaaki o o o 0 0 Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Process for Producing Polyester Resin Foam The following statement is a full description best method of performing it known to me/us:of this invention, including the 5845/3 1 Process For Producing Polyester Resin Foam Technical Field This invention relates to a process for producing a thermoplastic polyester resin foam.

Background Art Thermoplastic polyester resins such as polyethylene terephthalate and polybutylene terephthalate have excellent mechanical characteristics, heat resistance, chemical resistance and dimensional stability and are widely used in the fields of injection-moulded articles, fibres and films. However, it is difficult to obtain the desired viscoelastic properties during melting such that foams can be obtained. A blowing agent is easily released during foam extrusion and it is difficult to obtain good foams wherein fine closed cells are uniformly formed. To solve this problem, a method was proposed wherein diglycidyl esters are incorporated in aromatic polyesters in the foam extrusion of the aromatic polyesters. More specifically, polyfunctional diglycidyl esters and *i0 15 polyfunctional carboxylic acid anhydrides are incorporated in thermoplastic polyesters to improve the melt viscosity of the thermoplastic polyesters.

The present inventors have been engaged in the production and study of extruded ;"foams for many years. In their experience when the foam extrusion comprising a Sthermoplastic polyester in admixture with diglycidyl ester compounds is subjected to a continuous long run, the resulting foam becomes discoloured. The present inventors have surprisingly found that when pyromellitic dianhydride is mixed with a thermoplastic S: °polyester without using any diglycidyl ester compound, the resulting foam is not coloured and burned, even when foam extrusion is continuously conducted over a long period of time. This process has been described in Australian Patent Application No. 45797/89 and :0 25 is incorporated herein by reference.

Australian Patent Application No. 45797/89 also describes that when compounds having two or more acid anhydride groups per molecule such as pyromellitic dianhydride and compounds of Group I, II or III metals of the Periodic T'able are added to thermoplastic polyester resins, the viscoelasticity of the molten materials is improved and at the same time, there can be obtained foams having high tensile elongation and more finer cells.

Pre-expanded foam when extended through an extruder has only a tow expansion ratio and usually a high density. Also, the heat resistance of such foams is not acceptable for many applications.

Object Of The Invention It is an object of the present invention to provide a process for producing a thermoplastic polyester resin foam which is highly expanded and has excellent heat IG:\WPUSER\LIBR100086:KEH 1 of 18

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2 resistance. This is accomplished by re-heating an extrusion-expanded thermoplastic polyester resin foam to carry out post-expansion.

Brief Description Of The Drawings Figures 1 to 3 are sectional views of means for carrying out re-heating according to present invention.

Figure 4 shows diagrammatically one embodiment of a means for continuously carrying out re-heating according to the present invention.

Disclosure Of The Invention There is provided in the present invention a process for producing a thermoplastic polyester resin foam, comprising cooling a high-temperature thermoplastic polyester resin foam, immediately after expansion, to a temperature of not higher than the glass transition point of the resin to bring crystallinity to from 9 to 30% and then heating the foam to 600 C or higher, said thermoplastic polyester resin comprising a linear polyester of a polycondensate of an aromatic dicarboxylic acid component and a diol component.

In the present invention it is preferred to use the extrusion method of foaming the thermoplastic resin wherein the resin is melted under high temperature (approximately 270 0 C) and high pressure in an extruder and then extruded through a die into a low pressure zone (such as at atmospheric pressure) to produce foams. Other foaming methods may however be used.

Thermoplastic polyester resins used in the present invention are linear polyesters of polycondensates of an aromatic dicarboxylic acid component and a diol component.

Examples of dicarboxylic acid components which can be used in the present C invention include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyl ether carboxylic acid, diphenyl sulfonedicarboxylic acid and diphenoxyethanedicarboxylic acid.

Examples of diol components which can be used in the present invention include ethylene glycol, trimethylene glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, cyclohexanedimethanol, tricyclodecanedimethanol, 2,2-bis(4-phydroxyethoxy-phenyl)propane, 4,4-bis(P-hydroxyethoxy)diphenyl sulfone, diethylene glycol and 1,4-butanediol.

Polyethylene terephthalate, polybutylene terephthalate, polybutylene terephthalate elastomer, amorphous polyesters, polycyclohexane terephthalate, polyethylene naphthalate and mixtures thereof are preferably used as the polyesters comprising these dicarboxylic acid components and these diol components. Modified resins composed of at least of these thermoplastic polyester resins can also be used.

The pre-expanded foam is cooled to a temperature of not higher than the glass transition point of the polyester resin. The glass transition point of the polyester resin Svaries depending on the types of carboxylic acids and alcohols which constitute I 'i~ t Oo St a o t f rroo i i tl ot a o 00.6 t 6 0 1 3 polyesters, but is generally in the range of 30 to 90°C. Hence, the foam is generally cooled to a temperature of not higher than When the pre-expanded foam is cooled, it is settled without having a time to crystallise, and hence the crystallinity thereof is low.

The crystallinity varies depending on the degree of cooling. For example, the crystallinity varies depending on the type and temperature of cooling media and the contact conditions of the foam with the cooling media. When the pre-expanded foam prepared by extrusion is brought into directly contact with water at room temperature, the crystallinity thereof is several, generally not higher than 30%. However, when the preexpanded foam prepared by trusion is put into a mould to shape it, crystallinity becomes 30% or higher, since the foam is not cooled unless the mould is forcedly cooled.

Particularly, the crystallinity of thick-wall pre-expanded foam becomes 30% or higher.

Accordingly, when the pre-expanded foam is prepared by means of the extruder, the foam is allowed to proceed along a cooled mould to thereby cool it.

In order to conduct effectively the cooling of the pre-expanded foam, it is desirable that the foam has a large surface area in comparison with its volume. Namely, it is desirable that the foam is in the form of a sheet, if possible and its thickness is not more than 10mm, preferably not more than 3mm.

When the sheet is cylindrical, a mandrel is put into the inside of the cylinder, the sheet is allowed to proceed along the mandrel which is cooled with water and the length of the mandrel should be as long as possible.

On the other hand, when the sheet is a flat sheet, the sheet is put between a pair of rollers and allowed to proceed while cooling and at the same time, the rollers are cooled with water and the diameters of rollers should be as large as possible.

25 In this way, the crystallinity of the pre-expanded foam is brought to 30% or below.

The foam is then re-heated to carry out post-expansion (secondary expansion). For post-expansion, the foam is heated to 60 0 C or higher. Any type of heating means can be used. For example, heating may be conducted by conduction in contact with a heating plate. Alternatively, heating may be conducted by radiation, convection or highfrequency power. Any type of heating media can be used, so long as polyester resins are not deteriorated by them. A preferred heating method is such that the pre-expanded foam is brought into contact with a heated metal or air or with steam or heated water.

The heating time for the post-expansion is determied according to the properties of the resins, the shape and the type and temperature of the heating medium. Generally, when the temperature of the heating medium is low, heating time is prolonged, while when the temperature is nigh, heating time is shortened. Further, when the foam is thickwalled, heating time is prolonged, while when the foam is thin-walled, heating time is shortened.

IG:\WPUSER\LIBR100086:JOC 3 of 18 4 It is preferred that a metal plate is heated to 60 to 200 0 C and the pre-expanded foam is brought into contact with the metal plate for 5 seconds or longer when the foam is heated by bringing it into contact with the metal plate.

When the pre-expanded foam is heated by bringing it into contact with air, it is preferred that the foam is put into an oven, the temperature within the oven is elevated to 100 to 230 0 C and the foam is heated for 10 seconds to 5 minutes. It is desirable that when the foam is heated by the metal plate or air, the foam is left to stand for at least 24 hours, usually about 3 days after the pre-expansion and then is subjected to the postexpansion without conducting post-expansion immediately after pre-expansion.

On the other hand, when the pre-expanded foam is heated by bringing it into contact with steam or hot water, post-expansion can be carried out immediately after preexpansion. In this case, the temperature of steam or water is 60 to 125 0 C and contact rT time is 10 seconds to 5 minutes.

The polyester resin foam can be brought into contact with steam or water by various methods. For example, the foam 1 may be immersed in heated water 2 as shown in Fig.

S0°*4°0 1. In Fig. 1, a numeral 8 means a burner. In another embodiment, a metal gauze 3 is o o placed above the surface of heated water and the foam 1 is placed on the metal gauze 3 and is brought into contact with steam 4 which is evaporated from water 2 as shown in 2 Fig. 2. In other embodiment, pressurised steam 4 is blown into a container 9 containing S 20 the foam 1 as shown in Fig. 3.

It is preferred that the foam is placed in a mould and moulded into a desirable shape when the foam is to be heated by bringing it into contact with water or steam. When a mould is used, water or steam is allowed to introduce into the mould to thereby bring the 4" foam into directly contact with water or steam.

When the polyester resin foam is heated to 60 0 C or higher by bringing it into contact with water or steam in the manner described above, the foam is post-expanded to 000 form a foam having a low density. Generally, highly post-expansion can be easily conducted by heating with water or steam rather than air. Further, steam is more preferable than water. When heating is conducted with water or steam, the post-expansion ratio is at least 1.3 though it is lower than the pre-expansion ratio, and it is possible that the ratio is 4 or more. In addition thereto, expansion can be uniformly carried out and the resulting post-expanded foam has fine, uniform cells. In this way, a low density foam of good quality can be obtained.

Crystallinity is determined from quantity of heat of cold crystallisation and quantity of heat of fusion in heating by heat-flux DSC (differential scanning calorimetry) in the measurement of heat of transition according to JIS-R-71222 (Method for measuring heat of transition of plastics). Namely, crystallinity is determined by the following equation.

Crystallinity (Quantity of heat of fusion per mol (Quantity of heat of cold crystallisation per mol )x1O Quantity of heat of fusion per mol of perfect crystallised resin |G:\WPUSER\LIBR100086:JOC 4 of 18 Crystallinity was measured by using differential scanning calorimeter DSC 200 manufactured by Seiko K.K. For the quantity of heat of perfect crystal fusion of poly ethylene terephthalate, there was used 26.9kJ/mol from Kobunshi Deta Handobukku (published by Baifukan KK).

Molecular orientation ratio in the direction of face of foam sheet is the ratio between the maximum value of intensity of microwave transmitted through foam sheet and the minimum value thereof when the surface of foam sheet is perpendicularly irradiated with a polariser (manufactured by Kanzaki Paper Mfg. Co., Ltd.).

In a preferred process, compounds having two or more acid anhydride groups per molecule may be added to the thermoplastic polyester resins. By adding the compounds having two or more acid anhydride groups per molecule, the viscoelastic properties of the thermoplastic polyester resins during extrusion can be improved, whereby gasified blowing agents can be retained in the interiors of closed cells and uniformly dispersed fine cells can be formed using extruders.

It is believed that the compound having two or more acid anhydride groups per molecule is bonded to OH groups in the molecular chain of the thermoplastic polyester resin and cross linking gently takes place, whereby the viscoelastic properties of the thermoplastic polyester resin during extrusion can be improved.

The term "viscoelastic properties during melting" can be confirmed by a phenomenon wherein the molten resin is swollen or shrunk from the outlet of the die when the molten resin is extruded through the die, and can be generally represented by a die swell ratio. The die swell ratio can be measured when a molten resin is extruded t s through a round orifice die having a circular section. Die swell ratio can be determined by the following formula.

S. (Diameter of extruded melt) Die swell ratio S 25 Die swell ratio (Diameter of outlet of die) Die swell ratio is an important factor in extrusion foaming. It is preferred that die swell ratio is 2 to 5 in order to obtain foamed articles having a large sectional area and 00 uniformly dispersed fine cells in particular.

Where a blend of a thermoplastic polyester resin and a compound having two or more acid anhydride groups is molten in an extruder, a blowing agent is generally injected into the molten blend and the resulting molten blend is extruded through the die of the extruder for foaming into a low-pressure zone to produce a foam.

A compound of a metal of Group I, II or III elements of the Periodic Table may also be added to a thermoplastic polyester resin. In the same manner as that described above, the resulting blend is fed to an extruder to produce a foam. By adding a compound of a metal of Group I, II or III elements of the Periodic Table, there can be obtained a thermoplastic polyester resin foam having finer cells uniformly dispersed therein.

IG:\WPUSER\LIBR1OOO8:JOC 6 of 18 6 Any aromatic acid anhydride, cyclic aliphatic acid anhydride, fatty acid anhydride, halogenated acid anhydride, etc. can be used as the compound having two or more acid anhydride groups per molecule, so long as they have at least two acid anhydride groups per molecule. Further, mixtures thereof and modified compounds thereof can be used.

Preferred examples of the compounds include pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, diphenylsulfone tetracarboxylic dianhydride and 5-(2,5-dioxotetrahydro-3-furanyl)-3methyl-3-cyclohexen-1,2-dicarboxylic dianhydride. Among them, pyromellitic dianhydride is more preferred.

The compounds having two or more acid anhydride groups per molecule are used in an amount of preferably 0.05 to 5.0 parts by weight per 100 parts by weight of the thermoplastic polyester resin. When the amount of the compound having two or more acid anhydride groups per molecule is less than 0.05 part by weight per 100 parts by weight of the thermoplastic polyester resin, an effect of improving the viscoelastic properties of the thermoplastic polyester resin during extrusion is not sufficient and good foam cannot be formed, while when the amount exceeds 5.0 parts by weight, the gelation o°o of the molten material of the thermoplastic polyester resin proceeds and extrusion foaming Scannot be effected.

Any inorganic compound or organic compound can be used as the compounds of metals of Group I, II or III elements of IUPAC Periodic Table, so long as they have these metals as their constituent atoms. Examples of the inorganic compounds include potassium chloride, sodium chloride, sodium hydrogen carbonate, sodium carbonate, S potassium carbonate, zinc carbonate, magnesium carbonate, calcium carbonate, o aluminium carbonate, sodium oxide, potassium oxide, zinc oxide, magnesium oxide, calcium oxide, aluminium oxide and the hydroxides of these metals. Examples of the Sorganic compounds include sodium stearate, potassium stearate, zinc stearate, magnesium 'o e stearate, calcium stearate, aluminium stearate, sodium montanate, calcium montanate, lithium acetate, sodium acetate, zinc acetate, magnesium acetate, calcium acetate, sodium 0° caprylate, zinc caprylate, magnesium caprylate, calcium caprylate, aluminium caprylate, sodium myristate, zinc myristate, magnesium myristate, calcium myristate, aluminium myristate, calcium benzoate, potassium terephthalate, sodium terephthalate, sodium c ethoxide and potassium phenoxide. Among them, the compounds of Group I or II metals 1 of the Periodic Table are preferred and the compounds of Group I metals are more preferred. By using the compounds of Group I, II or III metals, the cells of the resulting thermoplastic polyester resin foam are made finer and at the same time, an effect of increasing the viscoelasticity by the compound having two or more acid anhydride groups per molecule can be increased.

The compounds of Group I, II or III metals of the Periodic Table are used in an amount of 0.05 to 5.0 parts by weight per 100 parts by weight of the thermoplastic [G:\WPUSER\LIBR100086:JOC 6 of 18 polyester resin. When the amount of the compound is less than 0.05 part by weight, effects of making the cells of the resulting foam finer and the efficiency of increasing the viscoelasticity by the compound having two or more anhydride groups are not sufficient, while when the amount exceeds 5 parts by weight, the resulting foam is coloured and the viscosity of the molten thermoplastic polyester resin is not high enough.

A blowing agent can be used in the production of the thermoplastic polyester resin foams in the pre-expansion step. Any blowing agent can be used providing they are easily j vaporisable liquids or thermally decomposable chemicals. Easy vaporisable blowing agents such as inert gases, saturated aliphatic hydrocarbons, saturated alicyclic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons, ethers and ketones are preferred. Examples of these easy vaporisable blowing agents include carbon dioxide, nitrogen, methane, ethane, propane, butane, pentane, hexane, methylpentane, dimethylbutane, methylcyclopropane, cyclopentane, cyclohexane, methylcyclopentane, ethylcyclobutane, 1, 1,2-trimethylcyclopropane, trichloromonofluoromethane, dichlorodifluoromethane, monochlorodifluoromethane, trichlorotrifluoroethane, dichlorotetrafluoroethane, dichlorotrifluoroethane, monochlorodifluoroethane, tetrafluoroethane, dimethyl ether, 2-ethoxyethane, acetone, methyl ethyl ketone, acetylacetone, dichlorotetrafluoroethane, monochlorotetrafluoroethane, dichloromonot fluoroethane and difluoroethane.

Usually, the blowing agent is injected into the molten blend of the thermoplastic polyester resin, the compound having two or more acid anhydride groups per molecule and other additives on the way of an extruder. The amount of the blowing agent to be S injected is from 0.05 to 50% by weight based on the amount of the molten blend. When the amount of the blowing agent is less than 0.05% by weight, the resulting foam is not sufficiently expanded, while when the amount is more than 50% by weight, the gas of the blowing agent is not accommodated for foaming, but blows off and the foam cannot be formed into a desired shape. The preferred amount of the blowing agent is 0.1 to 30% by weight based on the amount of the molten blend.

t 0 In the production of the thermoplastic polyester resin foams, stabiliser, expansion 30 nucleating agent, pigment, filler, flame retarder and antistatic agent may be optionally added to the resin blend to improve the physical properties of the thermoplastic polyester resin foams and moulded articles thereof. Foaming can be carried out by any of blow moulding process and extrusion process using single screw extruder, multiple screw extruder and tandem extruder. Dies used in the extrusion process or the blow moulding process are flat die, circular die and nozzle die according to the shape of the desired foam. In the production of the polyester resin foams as used in the present invention, the thermoplastic polyester resin can be mixed with the compound having two or more acid anhydride groups per molecule and other additives by any of the following methods.

IG:\WPUSER\LIBRIOOO8:JOC 7 of 18 i. 8 The thermoplastic polyester resin is mixed with the compound having two or more acid anhydride groups per molecule at a low temperature a temperature of not higher than 150C). (For example, the powder of the compound having two or more acid anhydride groups per molecule is stuck on the pellet of the thermoplastic polyester resin).

The compound having two or more acid anhydride groups per molecule is previously melt-mixed with a thermoplastic resin, the mixture is pelletised and the pellet is mixed with the thermoplastic polyester resin (this thermoplastic resin may be the same as or different from the thermoplastic polyester resin, but is preferably one compatible with the thermoplastic polyester resin).

The thermoplastic polyester resin is previously fed to an extruder hopper to melt it and the compound having two or more acid anhydride groups per molecule is fed through a feed opening provided at the cylinder of the extruder to effect mixing.

In any of the above mixing methods, the moisture conteit of the resin blend should be as small as possible and is reduced to preferably not higher than 200 ppm. It is preferred that the thermoplastic polyester resin is dried at a temperature of 60 to 180°C with hot air having a dew point of not higher than -20 0 C in a dehumidifying hot-air dryer for about 4 hours.

Best Modes For Carrying Out The Invention The following Examples, Comparative Examples and Test Examples are provided to illustrate the present invention, but are not be construed as limiting the present invention in any way.

•Example 1 -Pre-expansion (primary expansion): TR8580 (trade name, a product of Teijin Limited) was used as polyethylene S 25 terephthalate (hereinafter referred to as PET).

PET was placed in a dehumidifying dryer and dried at 160°C for 4 hours while circulating hot air having a dew point of -30°C. 100 parts of PET, 0.6 part of talc, 0.35 part of pyromellitic dianhydride and 0.1 part of sodium carbonate were thoroughly missed in a tumbling mixer. The mixture was fed to an extruder (diameter of screw: L/D: 35) and thoroughly mixed a a screw revolution number of 25rpm and at a barrel temperature of 270 to 290 0 C. 1.3 parts of butane as a blowing agent per 100 parts of the mixture was introduced into the mixture under pressure on the way of the barrel. PET containing the blowing agent was extruded through the circular die into air to produce a tube. The die had a circular die gap of 0.4rmm and a bore of 60mm and was kept at 270 to 285°C. PET extruded into air was expanded and the tube as extruded was taken off while bringing it into contact with the outer surface of a cylindrical mandrel. The mandrel had an outer diameter of 205mm and cooling water at 30°C was circulated inside the mandrel so that the PET foam was quenched. The quenched PET foam was cut open IG:\WPUSER\LIBR0IOC,36:JOC 8 of 18 9 and the resulting flat foam sheet was wound up and referred to as pre-expanded foam sheet (primarily expanded foam sheet). The foam sheet was 643mm in width and had an apparent density (hereinafter referred to simply as density) of 0.26g/cm 3 a thickness of and a crystallinity of 9%.

Post-expansion (secondary expansion): A piece of 100 mm x 100 mm was cut off from the above pre-expanded foam sheet and subjected to post-expansion. The post-expansion was carried out by immersing the piece in warm water at 63 0 C for 5 minutes as shown in Figure 1. The thickness was expanded from 1.5mm to 2.1mm. The ratio V2/Vi of the volume (V2) of the post expanded foam sheet to the volume (V 1 of the pre-expanded foam sheet was 1.37. The post-expanded foam sheet had a density of 0.19g/cm 3 and a crystallinity of The post-expanded foam sheet was finely expanded and found to be a good foam.

Example 2 The same pre-expanded foam sheet as that obtained in Example 1 was used and o 15 post-expansion was carried in the same way as in Example 1 except that the temperature of warm water was 83°C and immersion was conducted for 5 minutes.

0444 There was obtained a post-expanded foam sheet which had a thickness of 3.02mm, a density of 0.13g/cm 3 and a crystallinity of 10%. The ratio V 2

/V

1 was 2.00. The foam sheet was finely, uniformly expanded, had a low density and was found to be a good foam.

Example 3 The same pre-expanded foam sheet as that obtained in Example 1 was used and -to post-expansion was carried out by bringing the sheet into contact with steam as shown in Figure 2. Namely, post-expansion was carried out by bringing the sheet into contact with S 25 steam at 62 0 C for 5 minutes.

There was obtained a post-expanded foam sheet which had a thickness of 2.51 mm and a density of 0.16g/cm 3 The ratio V 2

/V

1 was 1.63.

o Example 4 The procedure of Example 3 was repeated except that the temperature of steam for post-expansion was 75 0

C.

There was obtained a post-expanded foam sheet which had a thickness of 2.73mm and a density of 0.14g/cm 3 The ratio V 2 /Vi was 1.86.

Example The procedure of Example 3 was repeated except that the temperature of steam was 100 0 C and the contact time was 0.5 minute in the post-expansion.

There was obtained a post-expanded foam sheet which had a thickness of 2.78mm, a density of 0.14g/cm 3 and a crystallinity of 10%. The ratio V 2 /VI was 1.86.

IG:\WPUSER\LIBRI00085:JOC 9 of 18

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F Example 6 The procedure of Example 5 was repeated except that post-expansion was carried out by bringing the sheet into contact with steam at 100 0 C for 2 minutes as shown Figure 2.

There was obtained a post-expanded foam sheet which had a thickness of 3.92mm, a density of 0.10g/cm- 3 and a crystallinity of 16%. The ratio V 2 /VI was 2.60.

Example 7 The procedure of Example 5 was repeated except that post-expansion was carried out by bringing the sheet into contact with steam at 100 0 C for 5 minutes.

There was obtained a post-expanded foam sheet which had a thickness of 5.63mm, a density of 0.065g/crn 3 and a crystallinity of 26%. The ratio V 2 /V was 3.77.

Example 8 The procedure of Example 5 was repeated except that post-expansion was carried out by bringing the sheet into contact with steam at 100 0 C for 7 minutes.

qo 0 15 There was obtained a post-expanded foam sheet which had a thickness of 5.96mm oand a density of 0.065g/cm 3 The ratio V 2

/V

1 was 4.00.

Example 9 Post expansion was carried out in the same manner as in Example 8 by bringing the sheet into contact with steam at 100 0 C for 7 minutes except that post-expansion was carried out by placing a pre-expanded foam of 200mm x 280mm in an aluminium mould of 210mm x 290mm x There was obtained a post-expanded foam sheet which had a thickness of 5.00mm and a density of 0.07?g/cm 3 The ratio V 2 /Vi was 3.33. The sheet obtained was a flat foam sheet.

0 0 25 Example The same pre-expanded foam sheet as that obtained in Example 1 was used and post-expansion was carried out by blowing pressurised steam as shown in Figure 3.

Namely, post-expansion was carried by bringing the sheet into contact with steam at 110°C for 3 minutes.

There was obtained a post-expanded foam sheet which had a thickness of 3.41mm and a density of 0.1 lg/cm 3 The ratio V 2

/V

1 was 2.36.

Example 11 The procedure of Example 10 was repeated except that post-expansion was carried out by bringing the sheet into contact with steam at 120 0 C for 0.5 minute.

There was obtained a post-expanded foam sheet which had a thickness of 3.00mm and a density of 0.13g/cm 3 The ratio V 2

/V

1 was 2.00.

(G:\WPUSER\LIBRIOOOB:JOC 10 of 18 11 Example 12 Pre-expansion was carried out in the same manner as in Example 1 except that carbon dioxide was used as the blowing agent in place of butane and the amount of carbon dioxide was 1.1 parts. The resulting pre-expanded foam sheet was 643mm in width and had a density of 0.26g/cm 3 a thickness of 1.5mm and a crystallinity of 9%.

Post expansion was carried out in the same manner as in Example 7 to obtain a postexpanded foam sheet which had a thickness of 3.00mm and a density of 0.13g/cm 3 The ratio V 2

/V

1 was 2.00.

Example 13 The procedure of Example 1 was repeated except that post-expansion was carried out by using hot air at 80 0 C in place of warm water at 63°C and bringing the sheet into contact with hot air for 5 minutes to obtain a post-expanded foam sheet.

The post-expanded foam sheet was 2.1mm in thickness and had a density of 0.19g/cm 3 and a crystallinity of 10%. The ratio V 2

/V

I was 1.37.

oo 15 Example 14 0 The procedure of Example 13 was repeated except that the temperature of hot air in the post-expansion was 100 0 C to obtain a post-expanded foam sheet.

The post-expanded foam sheet had a thickness of 2.6mm, a density of 0.15g/cm 3 and a crystallinity of 10%. The ratio V 2

/V

1 was 1.73.

Example The procedure of Example 13 was repeated except that the temperature of hot air in 00 the post-expansion was 110°C to obtain a post-expanded foam sheet.

The post-expanded foam sheet had a thickness of 2.8mm, a density of 0.14g/cm 3 and a crystallinity of 12%. The ratio V 2

/V

1 was 1.86.

o o Example 16 The procedure of Example 13 was repeated except that the temperature of hot air in the post-expansion was 140°C to obtain a post-expanded foam sheet.

The post-expanded foam sheet had a thickness of 3.01mm, a density of 0.13g/cm 3 and a crystallinity of 25%. The ratio V 2 /V was 2.00.

Example 17 The procedure of Example 13 was repeated except that the temperature of hot air in the post-expansion was 230°C to obtain a post-expanded foam sheet.

The post-expanded foam sheet had a thickness of 4.04mm, a density of 0.097g/cm 3 and a crystiiinity of 26%. The ratio V 2

/V

1 was 2.68.

IG:\WPUSER\LIBR100085:JOC 11 of 18 s 12 Example 18 Pre-expansion: Pre-expansion was carried out in the same manner as in Example 1 except that the die provided at the extruder head was changed from the circular die to a flat die and a flat plate was used in place of the mandrel. The flat die had a straight line-form extrusion opening having a width of 150mm and a gap of 0.7mm. The flat plate was an aluminium plate of 500mm x 500mm which was cooled with water at 30 0 C. The foam sheet was extruded between the aluminium plates, whereby the extruded foam sheet was quenched.

In this way, a pre-expanded foam sheet was obtained. The foam sheet had a width of 200mm, a thickness of 5mm, a density of 0.52g/cm 3 and a crystallinity of 12.

Post expansion: Post expansion was carried out in the same manner as in Example 8 by bringing the above pre-expanded foam sheet into contact with steam at 100 0 C for 7 minutes. There was obtained a post-expanded foam sheet which had a thickness of 12.5mm and a density of 0.204g/cm 3 The ratio V 2

/V

1 was 2.55.

Example 19 Pre-expansion was carried out in the same manner as in Example 18 except that the temperature of the aluminium plates was slightly elevated and the cooling rate of the foam sheet was slightly smaller than that in Example 22 to obtain a pre-expanded foam sheet.

The width, thickness and density of the foam sheet were the same as those of the sheet of Example 22. However, the crystallinity was Post expansion: Post expansion was carried out in the same manner as in Example 18 to obtain a post-expanded foam sheet which had a thickness of 11.0mm and a density of 0.232g/cm 3 The ratio V 2

/V

1 was 2.44.

Comparative Example 1 The procedure of Example 5 was repeated except that post-expansion was carried out by using hot air at 60°C in place of wai n water at 63°C and bringing the sheet into contact with hot air for 5 minutes to obtain a post-expanded foam sheet.

The post-expanded foam sheet had a thickness of 1.5mm and a density of 0.26g/cm 3 The ratio V 2 /Vi was 1.00. Accordingly, the post-expansion did not substantially take place.

Comparative Example 2 The procedure of Example 1 was repeated except that the temperature of water in the post-expansion was lowered to 53°C to obtain a post-expanded foam sheet.

The post-expanded foam sheet had a thickness of 1.5mm and a density of 0.26g/cm 3 The ratio V 2

/V

1 was 1.00 as in Comparative Example 1. Accordingly, the post-expansion did substantially not take place.

IG:\WPUSER\LIBR00086:JOC 12 of 18 13 Comparative Example 3 The procedure of Example 2 was repeated except that the temperature of steam in the post-expansion was lowered to 58 0 C to obtain a post-expanded foam sheet.

The post-expanded foam sheet had a thickness of 1.5mm and a density of 0.26g/cm 3 The ratio V 2

/V

1 was 1.00. Accordingly, the post-expansion did substantially take place.

Comparative Example 4 Pre-expansion was carried out in the same manner as in Example 19 except that the temperature of the aluminium plates was elevated to a temperature higher than that of Example 23 and the cooling rate of the extruded sheet was smaller than that of Example 19 to obtain a pre-expanded foam sheet. The width, thickness and density of the foam sheet were the same as those of the foam sheet of Example 19. but the crystallinity thereof was 32%.

Post expansion was carried out by bringing the pre-expanded foam sheet into contact 15 with steam at 100 0 C for 7 minutes to obtain a post-expanded foam sheet which had a a 0a thickness of 5mm and a density of 0.52g/cm 3 The ratio V 2

/V

1 was 1.00. Accordingly, the post-expansion did substantially not take place.

Example In this Example, the pre-expansion and the post-expansion were continuously carried out as shown in Figure 4. In Figure 4, an extruder 5 worked in the same manner as in the pre-expansion of Example 1 and continuously delivered a pre-expanded foam sheet. Without winding up the pre-expanded foam sheet, the sheet was successively a ":introduced into a steam tank 6. The temperature of the surface of the sheet was lowered to 30 0 C before it was introduced into the steam tank 6. In Figure 4, a numeral 10 means a winding machine.

o The pre-expanded foam sheet was brought into contact with steam at 100°C in the steam tank 6 for 5 minutes to carry out post-expansion. The sheet was then cooled.

The resulting post-expanded foam sheet had a width of 645mm, a density of S"0.07g/cm 3 and a thickness of 5.5mm and was a low-density fine sheet which was expanded at a high expansion ratio and had fine, uniform cells.

Example 21 100 parts of polyethylene terephthalate pellets (trade name: TR8580, manufactured by Teijin Limited) was dried with hot air having a dew point of -20°C at 160°C for hours. 0.3 part of pyromellitic dianhydride, 0.1 part of sodium carbonate and 0.6 part of talc as an expansion nucleating agent were uniformly mixed w 1h the pellets in a tumbling mixer. The mixture was fed to the hopper of an extruder (screw diameter: 65mm, L/D: [G:\WPUSER\LIB R1O0008:JOC 13 of 18 14 Cylinder temperature was 265 to 290°C, the temperature of the extruder head was 265°C, die temperature was 265°C and number of revolutions of screw was 2.4% by weight of butane as a blowing agent was introduced into the mixture under pressure on the way of the cylinder.

Die used was a circular die having a diameter of 60mm and a circular die gap of 0.45mm. A tube was extruded through the port of the die into air and moulded into a cylindrical form by means of a cylindrical mandrel while expanding the molten resin and taking off the tube. Part of the resulting cylindrical foam was cut open and the resulting sheet was wound up. In this case, surface temperature was kept at 20°C while circulating cooling water in the cylindrical mandrel.

The resulting foam sheet had a density (Dl) of 0.225g/cm 3 a width of 640mm and a thickness of i.6mm. The sheet had a crystallinity of 9.7% and a glass transition temperature of 75 C.

A re-heating treatment was carried out by contacting the sheet with heating for seconds by using a hot plate having a surface temperature of 160°C. There was obtained a post-expanded foam sheet having a density (D2) of 0.133g/cm 3 and a thickness of 2.7mm. The ratio of D1/D2 by the heat treatment was 1.69. The crystallinity of the sheet was 24.3%. A sample of 100mm x 100mm was cut off from the sheet and heated at 200 0 C in a constant temperature bath for 30 minutes. The ratio Va/Vb of the volume (V) after heating to the volume (Vb) before heating was 1.02. It was found that the sheet was excellent in heat resistance.

Example 22 100 parts of polyethylene terephthalate pellets (trade name: PET10388, manufactured by Eastman Kodak Company) was dried with hot air having a dew point of 25 20 0 C at 160°C. The dried pellets, 0.25 part of diglycidyl terephthalate (Blemmer® DGT manufactured by Nippon Oil Fats Co., Ltd.), 0.1 part of sodium montanate and 0.6 part of talc as an expansion nucleating agent were uniformly mixed in a tumbling mixer.

S o" The mixture was fed to the hopper of the same extruder as that used in Example 42.

:The cylinder temperature was 280 to 290°C, the temperature of the extruder head was 2900C, the die temperature was 290 0 C and the number of revolutions of screw was 2.2% by weight of pentane as a blowing agent was pressure-fed to the mixture on the way of the cylinder.

The resulting foam sheet had a density (Dl) of 0.242g/cm 3 a width of 640mm and a thickness of 17mm. The crystallinity of the sheet was 10.6% and the glass transition temperature thereof was 76°C.

A re-heating treatment was carried out by contacting the sheet with heating for seconds by using a hot plate having a surface temperature of 160°C. The resulting sheet had a density (D2) of 0.147g/cm 3 and a thickness of 2.8mm. The ratio D1/D2 by the heat treatment was 1.65. The crystallinity of the post-expanded foam sheet was 24.4%.

[G:\WPUSER\LIBRIO0085:JOC 14 of 18 A sample of 100mm x 100mm was cut off from the sheet and heated at 200 0 C in a constant temperature bath for 30 minutes. The ratio V 2

/V

1 was 1.02.

Example 23 The extruded foam sheet obtained in Example 21 was contacted with heating for 6 seconds by using a hot plate having a surface temperature of 170°C to obtain a foam sheet having a density (D2) of 0.106g/cm 3 and a thickness of 3.4mm. The ratio of D1/D2 by the heat treatment was 2.12. The crystallinity of the post-expanded foam sheet was 16.7%.

A sample of 100mm x 100mm was cut off from the sheet and heated at 200 0 C in a constant temperature bath for 30 minutes. The ratio Va/Vb was 1.06.

Example 24 The extruded foam sh.;et obtained in Example 21 was heated with steam having a vapour pressure of 4atm for 30 seconds to obtain a foam sheet having a density (D2) of 0.157g/cm 3 and a thickness of 2. mm. The ratio D1/D2 by this heating was 1.43. The S 15 crystallinity of the post-expanded foam sheet was 24.3%.

I A sample of 100mm x 100mm was cut off from the sheet and heated at 200°C in a constant temperature bath for 30 minutes. The ratio V 2

/V

1 was 0.99.

Comparative Example A sample of 100mm x 100mm was cut off from the foam sheet which was extruded in Example 27. The crystallinity was The sample was heated at 200 0 C in a S constant temperature bath for 30 minutes. The ratio Va/Vb was 1.74. Heat treatment after extrusion was not made. Hence, the sheet was poor in heat resistance and greatly deformed.

SComparative Example 6 The extruded foam sheet obtained in Example 21 was heated with a hot plate having a surface temperature of 140 0 C for 10 seconds to obtain a post-expanded foam sheet. The S crystallinity was 13.1%. The sheet had a density of 0.114g/mol and a thickness of 3.15mm. The ratio D1/D2 by this heating was 1.97.

A sample of 100mm x 100mm was cut off from the sheet and heated at 200 0 C in a constant temperature bath for 30 minutes. The ratio Va/Vb was 1.11.

The results of Examples 25 to 27 and Comparative Examples 30 and 31 are shown in Tables 1 and 2.

(G:\WPUSER\LIBRIOOO8:J OC 16 of 18 Table 1 Foam Sheet Post-Expanded Foam Sheet Density Crystallinity Density D2 Crystallinity D1/D2 D1 (g/cm 3 (g/cm 3 Example 21 0.225 9.7 0.133 24.3 1.69 Example 22 0.242 10.6 0.147 24.4 1.65 Example 23 0.225 9.7 0.106 16.7 2.12 Example 24 0.225 9.7 0.157 24.3 1.43 Comp. Ex. 5 0.225 9.7 Comp. Ex. 6 0.225 9.7 0.114 13.1 1.97 Table 2 Foam Sheet (mm) Post-Expanded Foam Sheet (mm) MD TD Thickness MD TD Thickness V2/V1 Example 21 100 100 2.70 99.8 100.4 2.75 1.02 Example 22 100 100 2.80 99.9 100.3 2.85 1.02 Example 23 100 100 3.40 99.7 100.2 3.60 1.06 Example 24 100 100 2.30 99.5 99.5 2.30 0.99 Comp. Ex. 5 100 100 1.60 97.0 94.0 3.05 1.74 Comp. Ex. 6 100 100 3.15 99.4 99.4 3.55 1.11 MD: Direction of extrusion of foam sheet TD: Direction perpendicular to MD 5 It is clear from Tables 1 and 2 that the volumes of the sheets which were not heattreated are greatly changed and the sheets are poor in heat resistance. Further, even when the sheets were heat-treated, the sheet having a crystallinity of less than 15% are inferior in heat resistance.

I 4Q It 00 .1 o o 4 IGAWPUSER\LIBRIOOO8O:JOC le of Is

Claims (9)

1. A process for producing a thermoplastic polyester resin foam, comprising cooling a high-temperature thermoplastic polyester resin foam, immediately after expansion, to a temperature of not higher than the glass transition point of the resin to bring crystallinity to from 9 to 30% and then heating the foam to 60°C or higher, said thermoplastic polyester resin comprising a linear polyester of a polycondensate of an aromatic dicarboxylic acid component and a diol component.

2. The process as claimed in claim 1, wherein said foam is produced by extrusion foaming.

3. The process claimed in claim 1 or claim 2, wherein said heating is carried out by bringing the polyester resin foam into contact with steam or hot water.

4. The process for producing a thermoplastic polyester resin foam as claimed in claim 1 or claim 2, wherein said heating is carried out by bringing the polyester resin foam into contact with a hot plate.

5. The process claimed in any one of claims 1 to 4, wherein said foam is re- expanded 1.3 times or more by heating.

6. The process for producing a thermoplastic polyester resin foam, substantially as hereinbefore described with reference to any one of the Examples excluding the Comparative Examples.

7. The process for producing a thermoplastic polyester resin foam, substantially as hereinbefore described with reference to the accompanying drawings.

8. The thermoplastically polyester resin foam substantially as hereinbefore described with reference to any one of the Examples excluding the Comparative Examples. S 25

9, The thermoplastically polyester resin foam whenever prepared by the process as claimed in any one of claims 1 to 7. Dated 23 June, 1994 .0 0 k Sekisui Kaseihin Kogyo Kabushiki Kaisha Patent Attorneys for the Applicant/Nominated Person S 30 SPRUSON FERGUSON AA]00115LMM t 4 I c l II[ Process For Producing Polyester Resin Foam Abstract A process for producing a thermoplastic polyester resin foam comprising cooling a high-temperature thermoplastic polyester resin foam immediately after expansion to a temperature of not higher than the glass transition point of the resin to bring crystallinity to from 9 to 30% and then heating the foam to 60 0 C or higher for example in a water bath comprising a heater said thermoplastic polyester resin comprising a linear Ss,. of a polycondensate of an aromatic dicarboxylic acid component and a diol a* 00 o £o a t o S Figure 1.