HK1081607A - Method for brightening synthetic fibers and plastic with granulated optical brighteners - Google Patents

Description

Process for whitening synthetic fibres and plastics with particulate optical brighteners

Granular, dust-free and free-flowing nonionic optical brighteners for plastics are described in DE 10114696.5-44. In which the form of a granular material of the brightener is obtained by covering the brightener powder with a waxy substance.

DE 2656406 describes the preparation of low dust levels, preferably water-soluble optical brighteners, by addition of dust binders, where a dust-free mixture is produced. DE 3910275 describes a process for producing dye granules, in which a dye powder having a water content of from 10 to 15% by weight is pressed into agglomerates. According to US 3,583,877 it is also necessary to add solvents and insoluble additives, such as waxes, during the preparation of the basic dye granule material. It is likewise necessary for the processes described in EP 264049, EP 115634 or EP 612557 to be carried out in the presence of auxiliaries. WO99/05226 describes the granulation of water-soluble dyes or optical brighteners in the presence of extenders or other additives.

However, the granular materials prepared by the above-described process are not doubtless in the whitening of fibres spun from PES or PA, since the adhesion additives may cause problems during the spinning of the yarn or may impair the runnability of the spun yarn. For example, if the wax-like substance forms a cream and impairs the quality of the glycol, undesirable side effects may also occur during the recycling of the glycol. Furthermore, during fiber production or spinning, yellowing of the fibers with reduced whitening effect may occur during high temperature loads.

For these reasons, only powdered products have hitherto been used for fibre whitening of PET and PA in the course of fibre production, but these products do not flow and are prone to dust formation during the charging process. The ecological and toxicological disadvantages of these dusts associated therewith are known. During the metered addition of these powders, it may also lead to the formation of lumps or lumps on the inner wall of the container. The granular material or pellets have a good flow behavior and are therefore better suited for dosing devices. It is known practice to dose by means of masterbatches in which the optical brightener is dispersed in the polyester or plastic in high concentrations (up to 30%). However, the preparation of these masterbatches is very expensive and is also accompanied by the above-mentioned ecological and toxicological problems. In addition, if equipment dictates the use of an ethylene glycol/brightener dispersion, the brightener particulate material should be well redispersed in ethylene glycol.

It has now surprisingly been found that synthetic fibres and plastics can be brightened by means of particulate fluorescent whitening agents which can be obtained by compressing a brightener powder under high pressure and then comminuting it.

The present invention provides a process for whitening synthetic fibres and plastics, which comprises incorporating a particulate optical brightener into the synthetic fibres or plastics, wherein the particulate optical brightener is obtainable by compacting the optical brightener in powder form in a pressure compactor under a pressure of from 3 to 50 kilonewtons per cm of tube length, and then comminuting the resultant compact.

The particulate optical brighteners can be produced by compacting at a temperature, preferably adjusted under pressure conditions, and at a pressure of from 5 to 50 kilonewtons per cm of tube length, preferably from 10 to 35 kilonewtons per cm of tube length, in a conventional pressure compactor between rollers and other compacting apparatus sets, such as extruder apparatus sets. The resulting sheet or strand is then passed through a comminuting device to the desired size. In the case of compaction by means of pressure rollers, the optical brightener is fed onto the rollers by means of a screw for pre-compaction within the screw and for final compaction between the pressure rollers. The compaction temperature is reached without external heat supply and may be in the range of 15-60 c, preferably 20-40 c. The compaction process may be carried out with or without roller cooling, under nitrogen or under vacuum, as desired. The strand, spiral or sheet obtained by the compaction is pulverized into a desired size by a conventional method, and the resulting granular material is free from an oversize or undersize by a sieving process using two or more sieves. The preferred compacted particulate material has a diameter of preferably 0.3 to 3 mm. However, granular materials having smaller or larger diameters may also meet the desired requirements in their performance. The oversize or undersize material removed by screening is fed back to the granulation process.

The compaction granulation process may be carried out using a commercially available granulator (such as a K configuration series compactor available from BEPEX GmbH, Leingarten, or a WP 50/75, WP 17V Pharma, or WP 50/250 granulator available from Alexanderwerk AG, Remscheid).

The resulting granular material is characterized by non-dusting properties and has good free-flowing properties and stability even during long transport times. Furthermore, the granular material of the present invention is less prone to caking and caking during the dosing process, which significantly improves the ease of processing. Furthermore, it has been shown that the granular material of the present invention is again well dispersible by addition with stirring to, for example, ethylene glycol. Such dispersions are well pumpable and can therefore be dosed during the production of polyester fibres.

According to the invention, all nonionic fluorescent whitening agents can be granulated in this way. These granular materials are used for the whitening of fully synthetic organic polymers (plastics and synthetic fibres). Regardless of the chemical structure, fluorescent whitening agents are characterized in that they absorb in the range of 260-400nm and emit in the visible spectrum of 400-450 nm. Preferred optical brighteners are benzoxazoles, thiophenes, stilbenes or pyrazolines and coumarins. Particularly preferred optical brighteners are described by formulae 1 to 5:

r ═ H and/or CH₃

Depending on the plastic or synthetic fiber and the whiteness to be achieved, the amount of optical brighteners is generally from 1 to 1000ppm, based on the plastic to be brightened. Higher amounts are possible in certain cases. It is also possible to use amounts of from 0.1 to 30%, based on the total weight of the plastic or synthetic fibers, in the preparation of the preconcentrate. The optical brighteners can be used individually or in the form of mixtures. Synergistic effects may also occur here. It is also possible to granulate the optical brightener together with a shading dye (nuancerfarbstoff). It is, of course, also possible to granulate mixtures of the brightener granulate material with additives which do not have interfering effects during incorporation or further processing of the plastics or fibers, for example with fiber stabilizers or plastic stabilizers. The granular material of the present invention is useful for whitening high molecular weight organic materials. These materials may be of natural or synthetic origin. For example, they may be natural resins, drying oils or rubbers, or modified natural substances, such as chlorinated rubbers, cellulose derivatives. The granular material of the present invention is preferably used for whitening polymers prepared by addition polymerization, polycondensation or polyaddition. Among the types of plastics prepared by addition polymerization, the following are mentioned in particular: polyolefins, such as polyethylene, polypropylene, polyisobutylene, substituted polyolefins, such as polystyrene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetal, polyacrylonitrile, polyacrylic and polymethacrylic acids and esters thereof, or polybutadiene, and copolymers thereof. Among the types of plastics prepared by polyaddition and polycondensation, the following are mentioned: polyesters, polyamides, polyimides, polycarbonates, polyurethanes, polyethers, polyacetals, and also condensation products of formaldehyde with phenol or urea, thiourea or melamine.

The high molecular weight materials mentioned may be present alone or may be mixed in the form of a plastic mass or melt. However, it is also possible to add the granular material of the invention to the monomers on which it is based in each case and then to carry out the polymerization. The granular material of the present invention is particularly preferably suitable for whitening polyester.

In the process of whitening polyester fibers, the optical brightener can be metered in during the transesterification or esterification, during polycondensation or before spinning. For example, the optical brightener is metered in the form of a glycol dispersion or in the form of a powder or in the form of a masterbatch. For example, if the optical brightener is added to the mixing plant provided with the dried PET pellets by means of a dosing device (barrel) just before spinning, blockages may occur in the barrel (e.g. Tamaki Blender model 80D-LC-7K) during the dosing of the powder, which leads to an interruption of the dosing process. This problem can be avoided by using pellets or granular material. If the optical brightener is to be added to the esterification, transesterification process or to the polycondensation reaction in the form of a glycol dispersion, the brightener granulate material can be redispersed well by stirring, for example in a 15% strength brightener formulation.

Example 1

100 parts of the brightener of formula 1 in powder form are pressed in a WP 50/75 compaction/granulator (roller length 75mm, roller diameter 152mm) at a roller pressure of 16 kilonewtons/cm RL and a rotational speed of 8 rpm. This gives a 2mm thick compact which is granulated and gives pellets having a diameter of from 0.6 to 2 mm. The throughput of the roll was 31kg/h and the yield of product having a diameter of 0.6-2mm after screening was 85%. About 4.6kg of feed back was fed to the compaction process. The resulting granular material has good free-flowing properties and is dust-free. The dust characteristics of the granular material were measured photometrically with a deposited dust meter. The number of dusts was 1. The powdery substance of the brightener of formula 1 constituting the granular material has a dust number of 13. (1: no dusting, 16: highly dusting). Furthermore, the granular material redisperses well in ethylene glycol with simple stirring.

Example 2

1000g of dimethyl terephthalate (DMT), 720g of ethylene glycol, 0.23g of manganese (II) acetate were charged into a 21 flask equipped with a VA stirrer, a 20cm packed column and a condenser system. The heating bath was heated to 160 ℃ and after melting of DMT the stirrer was started and the apparatus was brought to N₂And (4) flushing by flow.

After the start of the removal of methanol by distillation, the temperature was raised by 10 ℃ every 15 minutes until 230 ℃ and 235 ℃ and maintained at this level until all methanol was distilled off.

Then 0.3g of Sb dispersed in ethylene glycol₂O₃、0.09g H₃PO₃、4.0g TiO₂(type A) and 0.1g of a particulate brightener of the formula

Was added to a flask of 21, which had been equipped with a condenser and vacuum pump for ethylene glycol distillation. The dispersion was obtained by stirring the mixture at room temperature for 15 minutes. The bath temperature was raised to 250 ℃ and the flask was flushed with pure nitrogen. Stirring was started as soon as the viscosity of the flask contents had reached an acceptable level.

After complete melting of the transesterified product, N is interrupted₂Flow and start the following polycondensation procedure:

at 790 mbar for 15min

15min at 520 mbar

15min at 250 mbar

15min at 130 mbar

15min at 55 mbar

15min at 12 mbar.

The process can be supplemented by increasing the temperature to 250 ℃ and 270 ℃ under a vacuum of at least 0.013 mbar, with the stirrer speed being kept constant at 180 rpm. After the desired viscosity was obtained, the heating system was removed and the flask, which would break during cooling, was accordingly protected.

Hydraulically breaking polyester material in CO₂After cooling, grinding. The material was dried at 120 ℃ for 5h and spun. This gives a uniformly whitened fibre with excellent whiteness effects.

Example 3

The procedure was as in example 2. However, the conventional powder form is used instead of the granular fluorescent whitening agent of formula 1. Undesirable dust formation occurs during opening of the storage container and during removal of the brightener. The whiteness effect was the same as in example 1.

Example 4

The procedure was as in example 2. However, the particulate fluorescent whitening agent of formula 1 is added to the transesterification process without difficulty and without dust formation together with ethylene glycol. A uniformly whitened fibre is obtained, which proves that here too a uniform dispersion of the granular material takes place.

Example 5

The procedure was as in example 2. However, a granular material of the whitening agent of formula 6 is used as the whitening agent. The dosing was carried out without dust formation and a uniform whitening effect was obtained.

Claims (5)

1. A process for whitening synthetic fibres and plastics, characterised in that a particulate fluorescent whitening agent is incorporated into the synthetic fibres or plastics, wherein the particulate fluorescent whitening agent is obtained by compacting the fluorescent whitening agent in powder form in a pressure compactor under a pressure of 3-50 kilonewtons per cm of tube length, and subsequently comminuting the compact obtained.

2. The process as claimed in claim 1, characterized in that the optical brightener which is incorporated in granulated form absorbs in the range from 260-400nm and emits in the visible spectrum from 400-450 nm.

3. A process according to claim 1, characterized in that the particulate fluorescent whitening agent is added to the monomers constituting the synthetic fibres or plastics and is then polymerized.

4. A process according to claim 1, characterized in that a particulate fluorescent whitening agent comprising a shading dye is used.

5. A process according to claim 1, characterized in that a particulate fluorescent whitening agent consisting of a mixture of a plurality of fluorescent whitening agents is used.