COLOURED POLYESTER CONTAINER AND ALSO PREFORM FOR SUCH A COLOURED CONTAINER, AND A METHOD FOR MANUFACTURING A COLOURED POLYESTER CONTAINER

Abstract: Described is a coloured container of polyester obtained by injection moulding of a preform starting from colourless polyester granulate to which a particulate dyestuff composition is fed. The particulate dyestuff composition used is a particulate intimate mixture of a dyestuff and/or a pigment and a solid wax-like carrier having a melting point above 45 °C. The preform obtained is converted to the final shape by blowing. The invention also relates to a preform and to a method for producing the coloured polyester container described.

Description: The present invention relates in the first place to a method for producing a coloured polyester preform by feeding a colourless polyester granular material which is mixed with separate particles of a dyestuff composition consisting of an intimate mixture of a dyestuff and/or pigment and a wax-like carrier to an injection moulding installation to produce a coloured preform. In producing a coloured container from polyester, for example, a coloured bottle from polyester, usually a two-stage method is employed in which, in the first place, a coloured preform is produced which is converted to the desired final shape in a second stage by blowing. This manner of working provides the possibility of allowing the manufacture of the preform and the conversion to the final shape in the second stage to take place at different places. The preform is, for example, produced centrally in a plastic material processing industry; the standard preforms are then transported to the various customers who have installations for converting the polyester work piece by means of an enveloping mould into the final shape. Such a manner of working entails appreciable savings in the transport costs and is therefore frequently used. To produce a coloured container from polyester, the possibility is known of starting from colourless polyester granular material which, prior to being introduced into the injection moulding machine, is mixed with a product which contains a dyestuff and/or pigment and which is added in a quantity such that the desired colour concentration in the polyester is reached. The coloured product may, for example, consist of a homogeneous coloured polyester granular material which contains, for example, 10% dyestuff and/or pigment or a paste consisting of dyestuff and/or pigment and a viscous liquid, for example, glycerol. In this connection, a container is understood to mean any product which is capable of containing a quantity of liquid, semisolid or solid product and may be formed by a bottle, a beaker, a tank, a dish, etc. A coloured polyester container which is obtained in the known manner described above has, however, the disadvantage that, starting from coloured polyester granular material as an additive, there is a restriction on the colour density range, while it is difficult to achieve a good colour homogeneity at high colour density. If a coloured paste is used, there is the disadvantage that, as a result of the incorporation of a liquid carrier in the polyester, a deterioration of mechanical properties of the polyester is observed, as a result of which the possible applications decline in number; moreover, the possibility exists that the liquid carrier used is leached out of the holder during use, which is undesirable for, for example, use with food-stuffs. It is also known from NL-A-80 03468 to use a dyestuff composition, which is obtained by setting a liquid mixture of pigments and an ester of an aromatic dicarboxylic acid with an alcohol i.e. a dyestuff composition comprising a pigment and a wax-like carrier. Said publication is however related to the use of said dyestuff composition for colouring polyvinylchloride, for the production of relatively thick-walled pipe fittings, lids, boxes and crates or the like during which the problems encountered with injection blow-moulding of coloured polyester are not encountered. A first object of the present invention is to provide a method for producing a coloured polyester preform, which can be converted into a container by blowing, said container having a homogeneous colouring, which can be produced in a colour density between wide limits, the mechanical properties of which do not differ, or virtually do not differ, from those of a colourless container and in which the ability of any agents used to be leached out is minimumal. According to the invention the method for producing a coloured polyester preform is characterized in that a stream of material of colourless polyester granular material is fed at elevated temperature to the injection moulding installation and the separate particles of the dyestuff composition are fed to the stream of polyester material at a temperature which is below the melting point of the wax-like carrier. Attention is drawn to the fact that the dyestuff compositions are also known per se from the Dutch patent application 8000464 by the Applicant. Surprisingly, it has been found that if such dyestuff compositions which contain products with a lubricant nature are used in polyester, such as, for example polyethylene terephthalate, and are fed to the stream of polyester material at a temperature which is below the melting point of the wax-like carrier, an extremely homogeneous and reproducible colouring can be achieved, while the mechanical properties are not affected, or are virtually not affected, the ability of the products with a lubricant natureto be leached out is minimal and the mechanical properties are virtually unchanged compared with a colourless material. In respect to the invention reference is also made to US-A-4 230 501 in which is described the colouring of polyester with a pigment composition resembling the dyestuff composition as used according to the present invention. However, in said patent publication solely the forming of coloured samples by extrusion is described. Not described is a polyester article which is formed by injection moulding starting from colourless polyester material in granulate form at elevated temperature to which a particulate dyestuff composition is fed during the injection moulding process, said dyestuff composition being at a temperature which is below the melting point of the wax-like carrier. The dyestuff composition is fed to the stream of polyester material at a temperature which is below the melting point of the wax-like carrier; to do this, use is advantageously made of a cooled feeder to prevent the high temperature of the polyester being communicated to the dyestuff composition particles, as a result of which it starts to melt or to clot. In particular, the wax-like carrier has a melting point above 45 °C and is expediently chosen from an ester of an aromatic decarboxylic acid and an alcohol, such as stearyl and cetyl phthalate, an ester of a polyhydric alcohol and an aliphatic carboxylic acid, such as an ester of pentaerythritol of glycerol and a fatty acid containing 12 to 18 carbon atoms, for example pentaerythritol monostearate, pentaerythritol tetrastearate, glycerol mono-, di- or tristearate and mixtures thereof, montan wax, carnauba wax, hydrogenated oils, etc. For a review of carrier materials to be used according to the invention, reference is made to the paper by A. Riethmayer, Gummi-Asbest Kunststoffe, 1965, Volume 18, pages 425-432 entitled "Gleitmittel für PVC" ("Lubricants for PVC"). In the paper referred to, a summary is given of many of the carrier materials which can be used with the present invention and which can be converted, in the manner as specified in the previously mentioned Dutch patent application 8000464, into dyestuff compositions for use in the method according to the present invention. Advantageously, the wax-like carrier is formed by a hydrogenated oil, such as hydrogenated castor or ricinus oil. The wax-like carrier may also consist of amorphous polyethylene terephthalate. The invention further provides a method for producing a coloured polyester container by converting a preform to the desired final shape by blowing, said method being characterized in that a preform is used, which is produced by the method according to the invention. The invention will now be explained by means of the following non-restrictive example. EXAMPLE Colourless polyethylene terephthalate granular material is dried at 170 °C for a minimum of 8 hours. To prevent the granular material attracting moisture again, it is introduced into the injecting moulding machine at the same temperature. Into this stream of material, a small stream of particulate dyestuff composition is introduced by means of a cooled screw feeder. The particulate dyestuff composition consists of a green dyestuff (solvent green 3) and a carrier with a melting point of 85°C (hydrogenated ricinus oil) in a ratio by weight of 1:1. In general, the quantity of dyestuff (or pigment with respect to the total quantity of dyestuff composition may be 10-60% by weight. The dyestuff composition is, in this case, fed in in a quantity of 0.1 part to 100 parts of colourless polyester granular material. Depending on the desired depth of colour, the quantity of dyestuff composition with respect to the total material quantity may be from 50 ppm to approximately 5% by weight; in particular, 0.1-2% by weight. In the injection moulding machine, the processing temperature of the polyethylene terephthalate is 300-320°C. From the preforms obtained in this manner, green-coloured polyethylene terephthalate bottles are produced which excel in colour homogeniety and which, as regards mechanical and chemical properties, are virtually completely equivalent to colourless polyethylene terephthalate bottles which have been manufactured from the same colourless granulate. The presence of small quantities of wax-like carrier does not therefore reveal itself, or virtually does not reveal itself, in the properties of the material and can be detected only by a chemical analytical method. In the present example the starting point for colouring the polyethylene terephthalate is a dyestuff which is soluble in the said material and in that case the coloured bottle obtained will be transparantly coloured. If a masking colouring is desired, the dyestuff will in general be used together with a pigment, a suitable pigment being, for example, titanium dioxide.

Claims: Method for producing a coloured polyester preform by feeding a colourless polyester granular material which is mixed with separate particles of a dyestuff composition consisting of an intimate mixture of a dyestuff and/or pigment and a wax-like carrier to an injection moulding installation to produce a coloured preform, characterized in that , a stream of material of colourless polyester granular material is fed to the injection moulding installation at a temperature of 150-170 °C and the separate particles of the dyestuff composition are fed to the stream of polyester material at a temperature which is below the melting point of the wax-like carrier. Method according to claim 1, characterized in that the dyestuff composition particles are fed to the stream of material of colourless polyester granular material using a cooled feeder with which the temperature of the dye-stuff composition particles is held below the melting point of the wax-like carrier until they enter the said stream of polyester granular material. Method according to claims 1 or 2, characterized in that the wax-like carrier has a melting point above 45 °C and consists of a hydrogenated oil, such as hydrogenated castor or ricinus oil. Method for producing a coloured polyester container by converting a preform to the desired final shape by blowing, characterized in that, a preform is used, which is produced by the method according to one or more of claims 1-3.

Inventors: BES, RICHARD FRANCOIS THEODOR, KNOL, JAN DIRK, Bes, Richard François Theodor
Applicants: HOLLAND COLOURS APELDOORN B.V.
Application year: 1988
Main classification: B29C45
IPC codes: B29B7, B01F15, B29C45, C08J3