MXPA00000879A - Transparent articles of polyester resin - Google Patents

Abstract

Transparent articles, in particular sheets, having a thickness greater than 5 mm obtained from polyalkylene terephthalate/isophthalate resin containing 5-20%of isophthalic acid units, characterised by an intrinsic viscositygreater than 0.8 dl/g;melt strength at 280 DEG C greater than 1 cN and melt viscosity at 280 DEG C greater than 2000 Pa.s for shear rates tending to zero and not less than 200 Pa.s for shear rates of 1000 sec<-1>.

Description

TRANSPARENT ARTICLES OF POLYESTER RESIN DESCRIPTIVE MEMORY The present invention relates to thick transparent articles that are obtained from polyalkylene terephthalate resins having suitable characteristics for the preparation of said articles. Thick transparent sheets which are obtained from amorphous thermoplastic polymers such as PVC, polymethyl methacrylate, polycarbonate and polystyrene are known. Said sheets have several disadvantages such as, for example, the presence of plasticizers in PVC, which tend to migrate to the surface or the difficulty of recycling sheets of PMMA and PC, and the flammability and fragility of the PMMA sheets. Relatively thin transparent sheets are known which are obtained from modified crystallizable PET having a cold crystallization temperature between 120 ° -160 ° C. It is known from US-A-2 965 613 that the copolyethylene terephthalate resins containing 5-15% of isophthalic acid units having an intrinsic viscosity of 0.5-0.7 dl / g, (which are obtained using known methods by esterification / polycondensation of mixtures of terephthalic and isophthalic acid or by transesterification with ethylene glycol of mixtures of terephthalate and dimethyl isophthalate and polycondensation of obtained glycol ethers) are crystallized although at a much lower rate than polyethylene terephthalate homopolymer: only when the content of the isophthalic acid unit is too high (25-85%) the resins are no longer crystallizable. In this case Tv is very low and makes the resin not suitable for the preparation of products that have sufficiently good mechanical properties. In US-A-4 234 708 copolymers of terephthalate / copolyethylene isophthalate containing 5-15% of units deriving from isophthalic acid are described having very high intrinsic viscosity and melt strength, suitable for preparation by blown extrusion of thin walled transparent containers. The copolymers are prepared by polycondensation of mixtures of terephthalic acid and isophthalic acid and ethylene glycol or by transesterification of mixtures of terephthalate and dimethyl isophthalate and subsequent polycondensation of the esters, in the presence of a branching agent such as, for example, trimethylolpropane and pentaerythitol and a chain terminator (benzoic acid and the like). The intrinsic viscosity of the resin obtained (which is less than 0.7 dl / g) is brought to values higher than 1 dl / g by solid state polycondensation (SSP). After the SSP, the resins have a higher viscosity in the molten state (104-105 Pa-s at temperatures of 265 ° C to 300 ° C in the absence of tangential cutting forces) that descends drastically, under the action of tangential cut, to values of 102-103 Pa-s. Said high sensitivity to tangential cutting efforts, although on the one hand suitable for blow molding operations, is not suitable for the preparation by extrusion of coarse products where it is necessary that the melt maintain a sufficiently high viscosity even under the action of tangential cutting efforts. Heat formed articles having a thickness of 1-20 mm which are obtained from crystallizable polyalkylene terephthalate sheets having a crystallization temperature between 120-160 ° C are known from WO-A-97 / 12,750 . In the examples are the sheets formed with heat with the thickness of 5 mm maximum. The possibility of preparing articles and thick transparent sheets having good mechanical properties starting from polyalkylene terephthalate resins has been considered, but the problem has not yet been solved at present. It has now been unexpectedly found that it is possible to prepare sheets and transparent articles having a thickness greater than mm starting from terephthalate / copolyalkylene isophthalate resins containing 5-20% isophthalic acid units, preferably 7-15%, having the following properties: - intrinsic viscosity greater than 0.8 dl / g; - melt strength greater than 1cN at 280 ° C; - viscosity in the molten state at 280 ° C higher than 2000 Pa-s for shear rates that tend to 0 and not lower than 200 Pa-s for shear rates of 1000 sec. "1. The crystallinity of the articles per it is generally less than 5% Resins containing isophthalic acid units greater than 7-8% do not have esoteric transitions in the cold crystallization DSC curves.The articles have good mechanical properties, in particular high impact strength even at low temperatures, and optimum optical properties Copolylalkylene terephthalate resins having the properties indicated above are prepared according to known methods of esterification of mixtures of terephthalic and isophthalic acid with alkylene glycols with 2-8 carbon atoms, for example ethylene glycol, 1,4-butanediol, and polycondensation of associated glycol esters or from mixtures of dimethyl esters by cross-linking rification / polycondensation and by polyaddition in the solid state of the resins thus obtained, operating in the presence of a dianhydride of a tetracaboxylic acid, preferably aromatic, to obtain an increase in the viscosity of the starting resin of at least 0.1 dl / g unit and melt strength values greater than 1 cN at 280 ° C. The intrinsic viscosity after the SSP is preferably between 0.9-1.2 dl / g and the melt strength is preferably greater than 2 cN and is generally between 5-20 cN, always at 280 ° C. The viscosity in the molten state between 2000-3500 Pa-s at 280 ° C for shear rates that tend to 0 is generally adequate; however, a higher viscosity can be used. The viscosity in the molten state at 280 ° C corresponding to the shear rates of 1000 sec. "1 is generally greater than 200 Pa.s The polyaddition reaction in the solid state is carried out using known methods operating at lower temperatures. at the melting point of the resin and greater than the Tv thereof, generally between 130-200 ° C. Before undergoing the reaction in the solid state, the first resin is subjected to a crystallization treatment for the purpose of avoid the phenomenon of adhering to the polycondensation reactor.The working temperature is generally between 130 ° C and 180 ° C using, for example, a fluidized bed.A polyethylene terephthalate containing 8-15% of isophthalic acid units is the preferred resin In addition to the copolymers of terephthalate / statistical copolyethylene isophthalate prepared as indicated above, block copolymers of vari the types, always having a content of isophthalic acid units of 5-20%, and are obtained, for example, by extrusion of copolyethylene terephthalate / isophthalate mixtures having a different content of isophthalic acid units, (for example, 2% and 15% of soft acid) in the presence of pyromellitic anhydride and polyaddition in the subsequent solid state to obtain the desired rheological characteristics. In this way the block copolymers obtained have a crystallization temperature which is generally between 130 ° and 180 ° C depending on the content of isophthalic acid. The terephthalate / copolyalkylene isophthalate resins can be used in mixtures with compatible amorphous polymers such as, for example, e-polycaprolactone, which is used in such quantities so as not to compromise the transparency characteristics of the articles. The transparency is determined by UV / VIS spectrophotometric measurements. The light transmission is greater than 50% in the wavelength range of 1100 to 450 nm. The tetracarboxylic acid dianhydride is mixed with the resin in amounts of about 0.05 to 2% by weight, preferably 0.1-0.6%, at the exit of the polycondensation reactor in the molten state or that was added in the extrusion phase of the resin. The mixing and residence times in the extruder are relatively short (may be several minutes). Pyromellitic dianhydride is preferred. Examples of other dianhydrides are 1, 2,3,4-cyclobutetracarboxylic acid dianhydrides, 3,3'-, 4,4'-benzophenone tetracarboxylic acid, 2,2-bis (3,4-dicarboxyphenyl) propane, and bis ( 3,4-dicarboxyphenyl). The transparent articles of the invention are prepared using molding, extrusion, injection, thermoforming or other technologies. The articles are used for indoor and outdoor applications (after stabilization with UV stabilizers).

Examples of applications are greenhouse panels, traffic signs, transparent parts for automobiles and machines, shelving and the like. The transparent sheets with a thickness greater than 5 mm and which can be up to 20 mm and more preferably are prepared by casting-extrusion using collection rollers maintained at temperatures such as, for example, 30 ° C in the first roller and higher temperatures in other rollers, to be able to provide sufficient adhesion of the sheet to the rollers themselves. Resin fusion strength values greater than 1 cN are necessary to be able to perform the operations.

Methods for measurements The intrinsic viscosity is determined in a 60-40 weight solution of phenol and tetrachloroethane at 25 ° C in accordance with ASTM D 4603-86. The rheological measurements are taken in accordance with ASTM D 3835 using a Goettfert rheometer at a temperature of 280 ° C. The melt strength is evaluated by measuring the force required to stretch the extruded material from the capillarity of a Goettfert Rheograph 2002 rheometer. For the measurement a Rheotens apparatus is placed on the outside of the capillarity of a Goettfert Rheograph 2002 rheometer The extrusion conditions are as follows: Piston speed: 0.2 mm / sec, die diameter: 2 mm, capillary length: 30 mm test temperature: 280 ° C. The measurements were taken when establishing an acceleration of 2.4 cm / sec2. Each test was repeated with the average result of the two that were recorded.

EXAMPLE 1 The preparation of a polyethylene terephthalate / isophthalate copolymer (CO-PET) containing 13.5% isophthalic acid (IPA) units, improved in the presence of 0.2% by weight of pyromellitic anhydride, having V.l. = 0.83 dl / g. A CO-PET containing 13.5% IPA (obtained by esterification of mixtures of teraphthalic acid and isophthalic acid with ethylene glycol and subsequent polycondensation of glycol esters, having an intrinsic viscosity of 0.62 dl / g is mixed in an interdentate double screw extruder and of counter-rotation with L / D = 21.5 The temperature profile in several zones of the extruder was 244/260/270/280/289 ° C and the rotation speed of the screws was 477 rpm The obtained polymer obtained a Vl = 0.71 dl / g The pellets were crystallized at 173 ° C for 0.5 hours and subsequently replaced at 168 ° C in a nitrogen stream with a residence time of 24 hours The intrinsic viscosity of the improved product was 0.83 dl / g.

The DSC curve (heating rate of 10 ° C / minute) showed a melting peak at 202 ° C with enthalpy by fusion of 37.2 J / g. The DSC curve of cold crystallization showed no peak crystallization. The viscosity of the polymer at 280 ° C was 2500 Pa-s for shear rates that tend to zero and 200 Pa-s for shear rates of 1000 sec "1. The melt strength of the copolymer at 280 ° C was 11.5 cN In this way the CO-PET obtained was extruded in a Breyer extruder to produce a 7.7 mm thick sheet The extruded sheet was collected in a three roll system which was maintained at a temperature of 30 ° C for the first, 56 ° C for the second and 60 ° C for the third, the sheet that was obtained was transparent, the transmission of light measured with a UV / VIS spectrophotometer was around 80% for wavelengths of 1100-700 nm 70% for wavelengths of 700-600 nm, 70% for wavelengths of 600-450 nm The DSC curve (first operation) showed a crystallinity of less than 2% .The impact resistance measurements (in accordance with ISO 190611) provided the following values at -25 ° C, 25 ° and 50 ° C. -25 ° 25 ° 50 ° Peak energy (J) 4.73 8.30 9.30 Peak force (kN) 8.15 8.97 8.50 Peak distortion (mm) 1.22 1.81 2.03 Total deformation (mm) 4.93 8.99 9.82 Total energy (J) 1.24 1.90 2.10 Resilience (kJ / m) 0.62 1.12 0.98 EXAMPLE 2 The test of example 1 was repeated with the only difference that a sheet of 10 mm in thickness was prepared.

The sheet was transparent and showed characteristics similar to those of the sheet of example 7 (absence of crystallinity, high resistance to impact even at low temperatures). In particular, impact resistance measurements provide the following information: -25 ° 25 ° 50 ° - Peak energy (J) 19.40 16.72 16.58 - Peak force (kN) 14.67 15.10 13.36 - Peak deformation (mm) 1.49 2.20 2.30 - Total energy (J) 10.84 17.31 17.23 - Resilience (kJ / m) 1.08 1.73 1.72 EXAMPLE 3 The test of Example 1 was repeated with the only difference that the amount of PMDA added to CO-PET was 0.5% by weight. The intrinsic viscosity after extrusion was 0.62 dl / g; after improving at 175 ° C for 17 hours it was 0.85 dl / g. The DSC curve (first operation) showed a crystallization peak at 137 ° C with enthalpy of 34.0 J / g and a melting peak at 247 ° C with enthalpy of 39.8 J / g. The sheets with a thickness of 7 mm obtained showed characteristics similar to those of the sheet of example 1.

EXAMPLE 4 A mixture of 50% by weight of CO-PET with 2.2% of IPA and with Vl = 0.8 dl / g and CO-PET with 13.5% IPA and with Vl = 0.61 dl / g (IPA of the mixture 7.8% by weight) containing 0.2% by weight of PMDA was extruded in a twin screw extruder of interdentate, counterbalancing of Berstorff Ze 40 with L / D = 21.5 using a temperature profile in several zones of the extruder of 246/268/272/286/289/295/300 ° C and a screw speed of 447 rpm. V.l. of the extruded polymer was 0.70 dl / g. The pellets were crystallized at 185 ° C for 0.5 h and subsequently improved to 175 ° C in a nitrogen stream for 16 hours. V.l. of the improved polymer was 0.85 dl / g. The DSC curve (first operation) showed a crystallization peak at 155.9 ° C with enthalpy of 30.8 J / g and a melting peak at 233.8 ° C with enthalpy of 31.7 J / g. The DSC curve of cold crystallization showed a peak at 177.2 ° C with enthalpy of 37.2 J / g. A lamination test was carried out under the conditions of Example 1 obtaining a sheet with a thickness of 7.7 mm with characteristics of transparency and impact resistance similar to those of the sheet of example 1. The crystallinity of the sheet was less than 2%.

EXAMPLE 5 The test of example 4 was repeated with the only difference that a sheet with a thickness of 10 mm was produced. The sheet was transparent and had high impact resistance characteristics.

EXAMPLE 6 The test of Example 4 was repeated with the only difference that was used with CO-PET with 2.2% of IPA having a V.l. = 0.59 dl / g.

The results obtained were similar to those of Example 4.

EXAMPLE 4 COMPARATIVE EXAMPLE 1 The test of Example 1 was repeated with the only difference that CO-PET was used with 13.5% of IPA with a V.l. = 0.82 dl / g, which was obtained by improving in the absence of PMDA. The DSC curve (first operation) showed a melting peak at 203 ° C with a fusion enthalpy of 37.9 J / g. The DSC curve of cold crystallization showed no peak crystallization. The measurement at melt strength at 280 ° C was not determinable (melt strength too low). The viscosity of CO-PET in the molten state at 280 ° C and with shear rates that tend to zero was 500 Pa-s and with shear rates at 1000 sec "1 was 150 Pa-s. lamination tests that would operate under the conditions of example 1 since the extruded sheet did not adhere to the winding rolls due to the low melt strength.

COMPARATIVE EXAMPLE 2 The test of Example 4 was repeated with the only difference that a content of 0.04% of PMDA was used in the CO-PET mixture with 2.2% and 13.5% of lPA. After extrusion the polymer had a V.l. = 0.69 dl / g and, after improving in a stream of nitrogen at 175 ° C for 31 hours (after crystallization at 185 ° C for 0.5 hours), of 0.85 dl / g. The DSC curve (first operation) showed a crystallization peak at 143.3 ° C with enthalpy of 31.8 J / g and a melting peak at 235.9 ° C with enthalpy of 34.5 J / g. The cold crystallization curve showed a peak at 180.6 ° C with enthalpy of 36.9 J / g. The melt strength measurement at 280 ° C could not be performed (melt strength too low). It was not possible to perform a rolling test under the conditions of Example 1, in which the sheet did not adhere to the winding rolls.

Claims (7)

NOVELTY OF THE INVENTION CLAIMS

1. - A transparent product with a thickness greater than 5 mm which has a crystallinity of less than 5% which was obtained from terephthalate / copolyalkylene isophthalate resin comprising 5-20% units that were derived from isophthalic acid and which have the following characteristics: intrinsic viscosity greater than 0.8 dl / g; melt strength greater than 1cN (measured at 280 ° C); melting viscosity at 280 ° C greater than 2000 Pa-s in the absence of tangential cutting forces and not less than 200 Pa-s in correspondence with shear velocities of 1000 sec. "1.- The products in accordance with the claim 1, further characterized in that the melt strength is between 5-20 cN and the melt viscosity is between 2000-3500 Pa-s for shear rates that tend to zero 3.- The products in accordance with claim 1 or 2, further characterized in that the content of isophthalic acid units is 7-15% 4. The products according to any of claims 1 to 3, further characterized in that the copolyalkylene terephthalate / isophthalate is a copolymer. which was obtained by known methods of esterification / polycondensation of mixtures of terephthalic and isophthalic acid or by transesterification with alkylene glycols of mixtures of terephthalate and isophthalate of dimethyl and polycondensation of the esters that were obtained and by polyaddition in solid state of the copolymer in the presence of a dianhydride of a tetracarboxylic acid to obtain intrinsic viscosity values greater than 0.8 dl / g and melt strength of at least 1cN. 5. The products according to any of claims 1 to 4, further characterized in that the copolyalkylene terephthalates / isophthalates are block copolymers which were obtained by extrusion of mixtures of terephthalate / copolyalkylene isophthalates having various contents of acid units isophthalic in the presence of pyromellitic anhydrides and polyaddition in subsequent solid state. 6. The products according to any of claims 1 to 5, further characterized in that the copolyalkylene terephthalates / isophthalates are chosen from copolyethylene terephthalates / isophthalates. 7. The products according to any of claims 1 to 6, further characterized in that the shape of the sheets has a thickness of 5-20 mm.