RU2572176C1 - Method for obtaining fluorescent polyethyleneterephthalate film - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods for processing polymer films, in particular polyethyleneterephthalate (PETP) ones, in order to carry out their superficial decoration and add them required properties. The main task of the invention consists in reduction of processing process duration and in obtaining PETP film, intensively luminescent in visible area of spectrum (fluorescent). Essence of the invention consists in the following: initial PETP film is exposed to glow electric discharge with current intensity 0.25-0.3 A and voltage 4-5 kV for 2-4 min in vacuum chamber with residual pressure 2-4 Pa with constant air supply. PETP film, processed by glow discharge, has intensive luminescence in visible spectrum area (fluorescence), excited by UV light with wavelength 254 and 365 nm.

EFFECT: application of the invention extends possibilities of obtaining polymer films with complex of specified optic characteristics.

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Description

The invention relates to methods for processing polymer film materials with the aim of surface treatment, to obtain a decorative and other effect, to give them the required properties, including optical, in particular luminescence in the visible spectrum (fluorescence).

The method may find application in the production of fluorescent polyethylene terephthalate (PET) films. Such film materials are used in lighting engineering, as well as printing as a means of protection against counterfeiting of products of value.

PET, like most synthetic polymers, due to its chemical nature and supramolecular structure, does not have luminescence in the visible spectrum (fluorescence).

Existing methods for imparting this property to polymeric materials are based on introducing phosphor fragments into macromolecules during the synthesis of high molecular weight compounds, or by incorporating phosphors into the composition of a polymer composition with its subsequent processing into a film. In relation to PET, the known methods due to the technological features of the film production (high processing temperature - 250-300 ° C, the need for its orientation, etc.) cannot be used.

To obtain PET films with the required properties, the most acceptable methods may be those based on the processing of films by wave energy or electric discharges (corona, glow, plasma).

The aforementioned methods of processing polymer films, including PET, are well known in practice. They are used primarily to activate the surface of films in order to increase adhesion to other polymers in the production of multilayer film materials [1. Kogan D.F., Gul V.E., Samarina L.D. Multilayer and combined film materials. - M. Chemistry, 1989, p. 190; 2. Polymeric film materials. Ed. Gulya V.E., M., Chemistry, 1976, p. 130-146].

RF patent No. 2190536 (MKI B44B 5/00, 2001) describes a method in which fluorescence excited by short-wave UV light (λ = 254 nm) is increased by 10-12% compared to the initial one due to irradiation of PET films with unfiltered UV light (λ = 240-400 nm) with a power of 2400-2600 W / m ² . In this case, the film practically does not fluoresce at an excitation wavelength of 365 nm.

This method according to the technical solution is the closest to the claimed object and is selected as a prototype. The disadvantages of the method are as follows - the film fluoresces only when excited by short-wave light, while fluorescence has a weak intensity and a pronounced color cast. In addition, a longer processing time is required. This together limits the practical use of films.

The main objective of the invention is to obtain a film material based on PET with increased fluorescence intensity and a specific color cast, as well as to reduce the time of its processing.

A positive result is achieved by the fact that the initial PET film is treated with a glow electric discharge (current strength 0.25-0.30 A, voltage 4-5 kV) for 2-4 min in a vacuum chamber with a residual pressure of 2-4 Pa with a constant influx air.

The effect of a glowing electric discharge on a PET film leads to the formation of free radicals, the structuring and oxidation of the surface layer. When the exposure duration is up to 4 minutes inclusive, noticeable changes in the physicomechanical properties of the films are not observed. This fact explains the choice of a glow discharge for processing a PET film.

As the processing time increases (5 or more minutes), the strength characteristics of the film increase, which is explained by a change in the structure in the surface layer as a result of crosslinking and oxidation of the polymer. As for the effect of electric discharges on the optical properties of PET films (light transmission, fluorescence, etc.), no information was found in the scientific and technical literature about this. But, judging by the ongoing processes, we can assume the possibility of the formation of chemical compounds and products of their subsequent transformations in the surface layer and, consequently, the appearance of certain optical effects.

Indeed, the film treated by the glow discharge of the PETF did not differ from the initial one in appearance and deformation-strength characteristics, as well as in light transmission in the visible spectrum. However, when irradiated with UV light with wavelengths of 254 and 365 nm, a bright yellow-green glow is observed with a maximum intensity at λ = 475 nm.

The fluorescence intensity has an increasing dependence on the duration of the processing of the PET film and, when exposed for 4 minutes, increases by at least 4-6 times with respect to the initial film.

Comparative analysis with the prototype shows that the proposed solution meets the criteria of the invention of "novelty", since from publicly available information there are no known methods for producing fluorescent PET films based on their surface treatment by a glow electric discharge.

This technical solution has an inventive step, as the published technological data do not explicitly imply the claimed technological regime and processing conditions for PET films.

The proposed technical solution is practically applicable, since standard equipment, devices, materials and technological methods can be used for its implementation.

To confirm the possibility of practical implementation of the invention, a transparent film was used with a constantly sticky adhesive layer covered with release paper. The basis of such a material is a 20 micron thick PET film. Samples of material in A4 format were fixed in special holders so that the surface of the PET was accessible for processing, and then placed in a chamber of a vacuum installation in which a residual pressure of 3.0 Pa was created and it was maintained at this level with a constant flow of air. The samples were processed by a glow discharge with a current of 0.3 A at a voltage of 4.5 kV for 1.0; 2.0; 3.0; 4.0 minutes

The fluorescence spectra of the samples subjected to glow-discharge treatment were recorded using an MPF-2A spectrofluorimeter from Hitachi (Japan). Spectrum recording conditions: the excitation wavelength is 254 and 365 nm (the emission gap is 12, the excitation gap is 10, and the gain is 6).

The figure (Fig. 1) shows the fluorescence spectra of a sample with a glow discharge treatment duration of 4 min. The spectra have a simple configuration with a maximum at λ = 475 nm for excitation wavelengths of 254 nm (1) and 365 nm (2). The fluorescence spectrum (3) is the initial one for the untreated film. The figure (Fig. 2) shows graphs of the dependence of the fluorescence intensity (I _fl. ) At λ = 475 nm on the processing time of film samples — for spectra at an excitation wavelength of 254 nm (1) and 365 nm (2).

It seems impractical to process films for more than 4 minutes, since this already leads to deep destructive transformations of PET and a change in the deformation-strength and optical characteristics.

Film samples treated with a glow discharge for a period of 2 to 4 minutes have a fairly intense yellow-green fluorescence. If they are used, for example, for laminating important printed matter, the intensity and specific color tint of the fluorescence of a transparent film with a constantly sticky layer can serve as criteria for the authenticity of the latter. It is also possible to use the developed PET-based film materials in lighting engineering to create various optical effects.

Using the proposed method for producing fluorescent PET film provides the following advantages compared to existing ones:

- expanding the possibility of obtaining polymer films with a set of new physical, mechanical and optical characteristics;

- The technology for the production of film materials with specified optical characteristics is being improved;

- reduces the duration of the processing operation of the film material based on PET.

Claims (1)

A method of obtaining a fluorescent polyethylene terephthalate film based on the processing of the initial film by electric discharges, characterized in that the process is carried out by a glow discharge with a current strength of 0.25-0.3 A and a voltage of 4-5 kV for 2-4 minutes in a vacuum chamber with a residual pressure 2-4 Pa with a constant flow of air.

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