AU650812B2 - Process for producing polyester resin foam sheet - Google Patents

Description

AUSTRALIA

12 S F Ref: 227622 PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name and Address of Applicant: Actual Inventor(s): Sekisii Kaseihin Kogyo Kabushiki Kaisha No. 25, Minami Kyobate-cho 1-chome Nara-shi Nara

J)APAN

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

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. Hence, 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 polyfunctional carboxylic acid anhydrides were incorporated in thermoplastic polyesters to improve the melt viscosity of the thermoplastic polyesters.

The present inventors have found 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 Table 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. This process has been described in Australian Patent Application No. 45794/89 and is incorporated herein by reference.

Object Of The Invention It is an object of the present invention to provide an extruded foam sheet of a thermoplastic polyester resin, which is excellent in formability such as thermoformability.

*6 6 6 6*6 .1 Disclosure Of The Invention According to a first embodiment of the present invention there is provided a thermoplastic resin foam sheet wherein said sheet is an extruded foam sheet of a 30 thermoplastic polyester resin comprising a linear polyester of a polycondensate of an aromatic dicarboxylic acid component and a diol component having a crystallinity of from 7 to 20% and a molecular orientation ratio of 4.5 or lower looking in a direction from the surface of the foam sheet.

In the production of the polyester resin foams of the present invention, extruders are Tyc(icy -+erMopeas/-F used. e ti. polyester resins are melted under an elevated pressure in the extruders and the molten resins are extruded through die into a low-pressure zone to produce foams.

P

IPrlv11114391D2:JOC 1 of 13 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 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 be used.

In the present process the melt viscosity, die swell ratio, etc. of the thermoplastic polyester resins are adjusted to produce extrusion foam sheets. The extrusion foam sheets of the thermoplastic polyester resins have a density of preferably not higher than 20 0.7g/cm 3 more preferably not higher than 0.5g/cm 3 When the density exceeds 0.7g/m 3 heat insulating properties, lightweight properties and cushioning properties as foam sheet are lost. It has been round that the extrusion foam sheets having a crystallinity of not higher than 20% and a molecular orientation ratio of not higher than 4.5 in the direction of face of foam sheet are preferred from the viewpoint of thermoformability. It is difficult to lower the crystallinity through the thickness, since the extrusion foam sheet immediately after extrusion has heat insulating properties. However, post thermoformability can be improved by lowering the molecular orientation ratio to a specific value or below.

The molecular orientation ratio of the extrusion foam sheet looking the direction 30 from the surface of foam sheet can be adjusted to 4.5 or below by controlling expansion in the direction of extrusion and in the direction crossing the extrusion direction. As a preferred method therefor, there is generally used a method using a circular die and a cylindrical mandrel. Namely, expansion in the direction of extrusion can be controlled by the ratio of the average flow rate of a foamed resin to a take-off speed in the direction of extrusion at the outlet gap of the circular die, and expansion in the direction crossing the extrusion direction can be controlled by the ratio (hereinafter referred to as blow-up ratio) of the diameter of the outlet of the circular die to the outer diameter of the mandrel.

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 IPrvil11 439102JOC 2 of 13 measurement of heat of transition according to JIS-R-71222 (Method for measuring heat of transition of plastics). Namely, crystallinity is determined by the follo\ 'ing equation.

Crystallinity (Quantity of heat of fusion per mol (Quantity of heat of cold crystallisation per mol x00 Quantity of heat of fusion per mol of perfect crystallised resin 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).

In the production of the polyester resin foams of the present invention, 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 dtring 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 molecule 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 20 phenomenon wherein the molten resin is swollen or shrunk from the outlet of 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 through Sa round orifice die having a circular section. Die swell ratio can be determined by the following formila.

Die swell ratio (Diameter of extruded melt) 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 "uniformly dispersed fine cells in particular.

A blend of a thermoplastic polyester resin and optionally a compound having two or more acid anhydride groups is molten in an extruder, a blowing agent is generally injected S 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 having two or more acid anhydride groups per molecule and further a compound of a metal of Group I, II or In 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 IPrdv1l114391D2:JOC 3 of 13 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.

Any aromatic acid anhydrides, cyclic aliphatic acid anhydrides, fatty acid anhydrides, halogenated acid anhydrides, etc. can be used as the compounds having two or more acid anhydride groups per molecule, so long as they have at least tvo 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-3furanyl)-3-methyl-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 of the molten material of the thermoplastic polyester resin proceeds and extrusion foaming 20 cannot be effected.

Any inorganic compound and organic compound can be used as the compound of Group I, n 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, potassium carbonate, zinc carbonate, magnesium carbonate, calcium carbonate, aluminium carbonate, sodium oxide, potassium oxide, zinc oxide, magnesium oxide, calcium oxide, Saluminium oxide and the hydroxides of these metals. Examples of the organic compounds include sodium stearate, potassium stearate, zinc stearate, magnesium stearate, calcium stearate, aluminium stearate, sodium montanate, calcium montanate, lithium acetate, 30 sodium acetate, zinc acetate, magnesium acetate, calcium acetate, sodium 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 ethoxide and 'potassium phenoxide. Among them, the compounds of Group I or II metals 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 HI 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.

IPriv 114391D2:JOC 4of 13 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 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 present process. Any blowing agent is suitable providing it is an easily vaporisable liquid or thermally decomposable chemical. 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, dichloromonofluoroethane 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 25 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.

30 Optionally, a stabiliser, expansion nucleating agent, pigment, filler, flame retarder and antistatic agent may be added to the resin blend to improve the physical properties of the thermoplastic polyester resin foams and moulded articles thereof. In the production of the thermoplastic polyester resin foams of the present invention, 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. 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.

IPriv1114391D2:JOC 6 of 13 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 150 0 (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 content 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 0

C

with hot air having a dew point of not higher than -20'C in a dehumidifying hot-air dryer for about 4 hours.

iiBest Modes Of Carrying Out The Invention The following Examples illustrate preferred embodiments of the present invention.

Examples 1 To 3 And Comparative Examples 1 To 4 The production unit of extrusion foam sheets, which was used in these examples and comparative examples was a single screw extruder (screw diameter: 65mm, L/D: The extrusion die was a circular die (bore: 60mm), and the circular die gap of the extrusion die was changed as shown in Table 2.

25 The cylindrical mandrel was a water-cooled mandrel (outer diameter: 205mm, L/D: In the compositions of extrusion foam sheets used in these examples and comparative examples, 100 parts by weight of polyethylene terephthalate (PET) was used as the thermoplastic polyester resin. The resin grade was changed as shown in Table 1.

30 0.6 part by weight of talc was used as the expansion nucleating agent per 100 parts by Sweight of PET. Melt property modifiers and metallic compounds used together witlh the modifiers were changed as shown in Table 1. Liquefied butane was used as the blowing agent in an amount given in Table 1.

Extrusion foam sheets used in Examples 1 to 3 and Comparative Examples 1 to 3 were produced in the following manner.

Polyethylene terephthalate was dried in a dehumidifying drier (160'C, dew point of for 4 hours. Predetermined amounts of polyethylene terephthalate, modifier, metallic compound and talc were mixed in a tumbling mixer. The mixture was fed to the IPrivl 11 14391D2:JOC 6of 13 extruder hopper and melt-mixed. Liquefied butane as the blowing agent was injected into the mixture on the way of the extruder. The mixture was extruded through the circular bore of the circular die into air in the form of a tube. The extrudate was taken while expanding the molten resin, and the foam was cooled by bringing it into contact with the outer surface of the cylindrical mandrel to shape it into a cylinder. Part of the cylindrical foam was cut open and wound up as the foam sheet.

The manufacturing conditions of the extrusion foam sheets used in these examples and comparative examples were as follows.

Temperature of feed zone of extruder: 275 to 285 C, temperature of compression zone of extruder: 285 to 295 0 C, temperature of me:ing zone of extruder: 265 to 285°C, temperature of extruder head: 265 to 285OC, temperature of circular die: 260 to 285 0

C,

injection pressure of blowing agent: 40 to 140 kg/cm 3 and extrusion pressure (head pressure): 50 to 120kg/cm 3 The number of revolutions of screw and take-off speed are shown in Table 2.

The resulting foam sheets were 640 to 643mm in width. The apparent density, thickness, crystallinity and molecular orientation ratio thereof are shown in Table The post thermoformer and thermoforming conditions of the extrusion foam sheets which were used for evaluation in these examples and comparative examples, were as follows.

S 20 The post thermoformer was a one-shot moulding machine for expanded polystyrene, which had a heating zone with infrared radiation and a press part with air cylinder. The moulding tool was a plag-assist press tool (bore: 180mm x 155mm, depth: 95mm) for container. Moulding conditions were such that 360mm x 360mm foam sheets were heated at 175 0 C in the heating zone for 15 seconds and immediately thereafter, contacted with 25 the thermoformer for 25 seconds to effect the moulding.

The resulting moulded articles were evaluated by the following criteria.

Appearance The whole of sheet was uniformly extended, could be moulded into the same shape as that of press tool and not br iken.

30 Sheet which could be moulded into the same shape as that of press tool, but part of surface was broken and cracks were formed.

Sheet which was greatly broken and could not be moulded.

Thickness Ratio The ratio of the thickness of the bottom of the moulded article to that of sidewall thereof. The mark shows that the article is greatly broken and measurement cannot be made.

Surface Profile The surface of the moulded article was smooth.

O The surface was partly uneven.

IPriv11114391D2:JOC 7 of 13 8 Ht The surface was considerably uneven.

Overall Evaluation Evaluation was made as a whole by taking all of the surface profile of the extrusion foam sheet and the appearance and thickness of the post thermoformed article into consideration.

Particularly superior S: Superior S: Bad The results are shown in Table 4.

**e e 6 e e [Priv11114391D2:JOC 8 of 13 9 Table 1 Polyethylene Terephthalate Modifier Metallic Compound Manufacturer Grade Name Amount Name Amount Amount of (Part by (Part by Blowing Weight) weight) Agent (wt%) Example 1 Eastman Kodak PET10388 Pyromellitic anhydride 0.3 Sodium carbonate 0.1 1.3 Company__ Example 2 Eastman Kodak PET10388 Pyromellitic anhydride 0.3 Sodium carbonate 0.1 1.3 Examp2le 3 Teijin Limited TR455OBH Pyromellitic. anhydride 0.5 Sodium carbonate 0.1 1.2 Comp. Ex. 1 Teijin Limited TfR8580 Tetrafunctional epoxy 0.2 Omitted 0.7 nitride_ Com. Ex. 2 Teij in Limited TR8580 Pyromellitic anhydride 0.5 Sodium carbonate 0.1 1.3 ICom Ex. 3 Teijin Limlited TR8580 Pyromellitic anhydride 0.3 Sodium carbonate 0.1 1.3 Com Ex. 4 -Teijin Limited TR8580 IPyromellitic anhydride 1 0.3 j Sodium carbonate 1 0.1 1 1.3 jG.NWPUSER\UBRI00084.J0C [GAWPUSR\UBRIOOB4:JOC9 of 131Priv11114391D2:J0C of3 9 of 13 a a a.

Table 2 Number of Die Circular Extrusion Take-off Blow- Revolutions of Temp Die Gap Rate Speed up Screw of (mnm) (Kg/Hr) (rn/min.) Ratio Extruder (rpm-) E~xampple 1 25 265 0.5 23.7 2.16 3.42 Example 2 25 280 1.0 21.4 2.18 2.63 Example 3 25 270 0.7 23.7 2.26 3.42 Comp. Ex. 1 25 265 0.7 21.0 0.72 3.42 Comp. Ex. 2 25 280 1.0 21.4 1.45 2.63 Comp. Ex. 3 25 260 1.0 22.9 1.29 2.63 Comp. Eix. 4 25 1270 0.7 21.0 11.78 13.42 Table 3 Apparent Thickness Crystallinity Molecular SDensity (g/cm 3 (mm) M Orientation Ratio Example 1 0.19 1.5 10 1.82 Example 2 0.18 1.7 11 1.73 Example 3 0.16 2.6 18 1.37 Comparative 0.63 1.2 4.27 Example 1 Comparative 0.19 2.0 11 4.88 Example 2 Comparative 0.23 2.0 10 5.36 Example 3 Comparative 0.18 1.7 22 1.701 Example 4 Table 4 Appearance of Thickniess Ratio of Surface Profile of Overall Mouldedi Article Moulded Article Moulded Article Evaluation Example 1 1.2 Example 2 1.3 Example 3 1.5 0© Comparative 4.1.3 Example 1I Comparative 0 Example 2 Comparative Example 3 Comparative 1Exa ple 4 IG:\WPUSEM\UBBR100084:JOC af1 10 of 13 Molecular orientation ratio can be adjusted by take-off speed and blow-up ratio, since when the take-off speed of the sheet is increased, the sheet is orientated in the MD dirction, while when the blow-up ratio is increased (cooling mandrel diameter is increased), the sheet is orientated in the TD direction. However, when the width and thickness of the sheet and expansion ratio are fixed, molecular orientation ratio cannot be properly adjusted only by the controlling of take-off speed and blow-up ratio. In this case, die temperature is elevated (Example 2, Comparative Example 2).

Molec.lar orientation ratio can be lowered by reducing the amount of the melt property modifier (Example 2, Comparative Example 1).

Crystallinity can be lowered by lowering the temperature of cooling water for cylindrical mandrel.

a oo o [G:\WPUSER\LIBR100084:JOC 11 of 13

Claims (6)

1. A thermopiastic resin foam sheet wherein said sheet is an extruded foam sheet of a thermoplastic polyester resin comprising a linear ester of a polycondensate of an aromatic dicarboxylic acid component and a diol component, has a crystallinity of from 7 to 20% and a molecular orientation ratio of 4.5 or lower looking in a direction from the surface of the foam sheet.

2. A thermoplastic resin foam sheet as claimed in claim 1, wherein said sheet has a density not higher than 0.7gcm- 3

3. A thermoplastic resin foam sheet as claimed in claim 1 or claim 2, wherein said sheet is an extruded foam sheet produced by using a circular die and a cylindrical mandrel.

4. A thermoplastic resin foam sheet as claimed in any one of claims 1 to 3, wherein said sheet is an extruded foam sheet of not more than 5mm in thickness.

A thermoplastic resin foam sheet substantially as hereinbefore described with S* 15 reference to any one of the Examples excluding the Comparative Examples.

6. A process for producing a thermoplastic resin foam sheet, substantially as hereinbefore described with reference to any one of the Examples excluding the S. Comparative Examples. SDated 20 April, 1994 Sekisui Kaseihin Kogyo Kabushiki Kaisha Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON IG:\WPUSER\LIBR]OO084:KEH 12 of 13 o Process For Producing Polyester Resin Foam Sheet Abjstract A thermoplastic resin foam sheet wherein said sheet is an extruded foam sheet of a thermoplastic polyester resin comprising a linear polyester of a polycondensate of an aromatic dicarboxylic acid component and a diol component having a crystallinity of from 7 to 20% and a molecular orientation ratio of 4.5 or lower looking in a direction from the surface of the foam sheet. IG:AWPUSEJWLIBRJOOO84.:JOC0 f1 0 of 13