DE4401207A1 - Identification of plastics packaging to facilitate recycling - Google Patents

Abstract

Process for identification of plastics packaging comprises the use of a fluorescent dye (I) in a concn. of 0.0005 wt.% in the matrix of a certain type of plastics. (I) can be identified by a definite, visible emission peak on stimulation with UV light with a wavelength of 363 nm. Also claimed is the use of different (I) for economically more efficient recycling, with a considerable time and energy saving.

Description

In the first half of 1993, 1.022 million tons of packaging material were used in Germany made from plastics [ANONYMUS (cr / vwd) (1993): Good future for plastics - Chemical Review 46 No. 44; 6].

In view of the resulting large amounts of waste, processes have been developed to to recycle high-energy plastic waste. A distinction is made here between the material and chemical recycling. The invention made is the material recycling area assign.

The previous state of the art in this area is injected by the water separation process or printed code or by the method based on infrared spectroscopy represents.

The main disadvantage of all methods is the high time required for the identification step and the associated high costs. These costs make the recycling granulate more expensive than newly produced raw material.

Due to the small density differences, there are several separation stages in the water separation process connected in series to achieve a satisfactory separation.

The abbreviations that only exist in one place, but often do not exist, are very time-consuming discover. In the event of mechanical damage to the packaging in the area of the code abbreviations Possibility of identification lost.

The infrared spectroscopy method is currently only being tested in a pilot process, and can only Identify products of a certain shape and from a certain size [ANONYMUS (cr / aw) (1993): Recycling of plastics - Chemische Rundschau 46 No. 3; 10].

The object of the invention is a mark invisible to the consumer, the one economically efficient sorting of the individual types of plastic by a significant time and energy gain.

This problem is solved by the plastic packaging through a defined, visible emission peak in a concentration of 0.0005 wt .-% in the Matrix of a certain type of plastic introduced fluorescent dye in a Can identify excitation wavelength of 365 nm.

Plastic packaging materials thus marked can be used using various Fluorescent dyes in different types of plastic due to different, more visible Emission peaks can be quickly identified and separated without much technical effort.  

The advantages of the invention

• a) No product discoloration due to the introduced fluorescent dye, so that crystal-clear packaging can also be marked.
• b) No mechanical change in the properties of the product due to the introduction of the Fluorescent dye.
• c) The fluorescent dyes used are non-toxic, therefore particularly good for use in Suitable for food packaging.
• d) The low price of the fluorescent dyes used.
• e) The possibility of further batch or manufacturer marking by different Defined emission peaks of a fluorescent dye in different plastic matrices is given.
• f) The identification can be due to the relative constancy of the emission peaks at under different excitation wavelengths with only one common excitation wavelength be made.
• g) The marked packaging can now the material recycling process several times can be supplied without much effort, which ver with a plastic waste reduction is bound.
• After further material recycling is out of the question, what due deteriorated mechanical properties mostly after 3-4 times, it will Only then is the plastic product sent for chemical recycling. So that becomes a achieved an economic increase in the entire recycling of plastics, as this material and chemical recycling from the point of view of saving raw materials (Chemical recycling now involves repeated use of recycling materials ahead) can be meaningfully linked.
• h) Furthermore, the visible fluorescence at a concentration of 0.0005 wt .-% dye expensive fluorescence spectrometer. The throughput at recognized Material is thus significantly higher (increase in profitability) since the emissions radiation can be perceived by simple photocells, and not every part must be measured separately in the sample chamber, and automation is possible.
• The photocells are provided with a filter, through which they are directed to a certain Spectral range can be tuned. Incident emission radiation in exactly this Spectral range triggers an impulse in the photocell, which is then sent to the sorting system is passed on. A robot arm equipped with photocells could serve as a sorting system act.
• i) A complete product marking is by melting the incorporated Fluo Resence dye guaranteed, with which partially soiled, broken or with products with fluorescent articles can be identified. Here is guaranteed on the one hand that the intensity of the product fluorescent radiation in the particular The spectral range is higher and thus the article imprint fluorescence, which only affects limited a narrow area, covered.
• On the other hand, the unpolluted area or the rest of the intact fluoresces Packaging.
• j) Malicious consumers cannot falsify the marking, as a complete change of the product coding is not possible.
• k) There must be no prescribed shape or size of the product due to the total coloring available. Small plastic spoons can be identified as well Quark cup.
• l) The separation can be done by the consumer at home with a simple bill test lamp are carried out, which is then due to the only required samples Would save time.

Description of exemplary embodiments

The process was carried out in preliminary tests on the plastics polystyrene 143 E (BASF), polyethylene Exxon PE-LD and Polypropylene Hostalen PPN 1060 natural due to their use as Packing material.

The organic LUMILUX color pigments CD 304, CD 307 were used to mark the plastics and CD 331 introduced into the test specimen. (LUMILUX is a registered trademark of Riedle-de Haen).

For the main experiments, polystyrene 143 E (BASF) was stained with CD 304 and CD 307.

The following test specimens were injection-molded for the preliminary tests:

• a) a standard tension rod according to DIN 16 770 for measuring mechanical properties
• b) a structured and smooth color measuring plate for measuring the color change.

In the main trials, the tool for manufacturing test specimens was used for testing the impact strength used.

For the preliminary tests, three different dye concentrations were used in the test specimen injection molded:

• a) 0.01% by weight of dye
• b) 0.0075% by weight of dye
• c) 0.005% by weight of dye.

The purpose of these preliminary experiments was to see whether a further reduction in concentration in the Main experiment on 0.0005 wt .-% dye coat made sense. In addition there were for each type of plastic Test specimens without added color.

The dye addition was 0.1 g / kg (a), 0.075 g / kg (b) and 0.05 g / kg (c) and was the Plastic granules mixed in. At 0.0005% by weight, this corresponded to 0.005 g of dye per kg.

Fluorescence spectroscopic investigations

Viewing the pre-samples under UV light with a wavelength of 365 nm.

Table 1 shows the appearance of the test specimens under UV light.

In order to obtain more precise values, the color measuring plates were fluorescence spectroscopic measured. First, the dyes applied to a slide were measured.  

For CD 304 (excited at 382 nm) the emission peak was 525 nm, with a difference of 20 nm to the delivery value of Riedel-de Haen occurred.

The emission peak of CD 307 is 472 nm after an excitation of 390 nm. CD 331 was excited at 367 nm, with an emission peak at 612 nm. The colored ones were used with the excitation wavelengths used for the respective dyes Irradiated plastics. The emission peaks that occurred were of such a low intensity that the colored plastics have now been irradiated with different wavelengths, in order to meet the new requirements find wavelength.

The excitation wavelength for the emission peak is for:
CD 304 in PP at 325 nm, in PS at 350 nm and in PE at 358 nm
CD 307 in PP at 384 nm, in PS at 390 nm and in PE at 384 nm
CD 331 in PP at 349 nm and in PE at 326 nm.

Because of the plastic matrix, the selected excitation wavelength must be shorter and more energetic so that the emission peak of the dye can be obtained and measured. This is due to the Absorption of the original excitation radiation by the plastic molecules, especially when Polystyrene through the benzene rings and the resulting free electron cloud (Mesomerism). The shorter excitation wavelength is more strongly absorbed, but in the end it has more energy than the original excitation wavelength, so that an emission peak occurs.

The test specimens were then measured in three different wavelengths:

• 1) with the original excitation wavelength of the dyes
• 2) with the changed excitation wavelength in the respective matrix
• 3) with 365 nm (corresponds to the emission peak of the commercially available black light lamps).

The color measuring plates were used for the measurements. Any five plates of a dye concentration were measured. As a comparison value plates from the pure material were also measured.

Polystyrene colored with CD 331 did not emit at the three wavelengths, even at one Excitation over the range of 300-400 nm showed no emission radiation. Even polystyrene with 0.02 wt% CD 331 had this effect. On the one hand, this can affect the free electron cloud of the benzene ring, which only have an effect on CD 331 as an emission control can. (Fluorescence occurs with CD 304 and CD 307). This would then fall into the category of solvent-dependent fluorescence fall. Secondly, a complete decomposition of CD 331 have taken place, but this is refuted by the presence of fluorescence in PE and PP.

The average value was formed from the five individual values. From the averages of the Colored plastics, the average value of the pure material was the same Wavelength subtracted. So you only got the emission radiation of the dye in art fabric matrix.

The emission peaks shown are average values formed from the measured peaks in the three concentration settings.

Table 2 shows the emission peaks of the dyes in the respective plastic matrix defined excitation wavelength.

As can be seen from the table, the emission peak remains even with different excitation wavelength equal. The only exceptions are polyethylene (CD 304; 382 nm) and Polypropylene (CD 304; 382 nm and 365 nm). This shift in emission peaks is due to the Plastic matrix attributed as a solvent because the dyes in different solutions show different fluorescence. In the case of polyethylene and polypropylene, there is still one The fact that different excitation wavelengths have different emission peaks cause, (very nice to see in the table). With polyethylene this only occurs with the original excitation wavelength. Polypropylene (CD 304) has two emission peaks, since there is only a slight difference in their intensity, and therefore one when irradiated with 365 nm Mixed fluorescent color (see Table 1) results.

Based on these positive results, polystyrene with 0.0005 wt .-% CD 304 and CD 307 dyed and color measuring plates injection molded. When viewed under UV light of wavelength 365 nm there was a visible yellowish fluorescence on CD 304 and a visible bluish fluorescence on CD 307 on; (CD 331 was not used due to the preliminary results). Because with polypropylene and Polyethylene had exactly the same results in the preliminary tests, this is also the case with one Guaranteed concentration of 0.0005 wt .-%.

Table 3 shows the emission peaks of 0.0005 wt% CD 304 and CD 307 in PS.

result

The identification of the colored plastic types with an excitation wavelength (365 nm) is possible, as there are no changes in the emission peaks except for polypropylene (CD 304), but all have the same value.

After these model tests, the procedure for identifying plastic packaging is included different fluorescent dyes without affecting the color and in the mechanical properties through visible fluorescence is possible.

Claims (2)

1. A method for identifying plastic packaging, characterized in that the plastic packaging can be identified by a defined, visible emission peak of a fluorescent dye introduced into the matrix of a specific type of plastic in a concentration of 0.0005% by weight at an excitation wavelength of 365 nm . 2. The method according to claim 1 using different fluorescent dyes for a host Economically more efficient material recycling with considerable time and energy savings.