RU2581093C2 - Method for producing fluorescing polymer film - Google Patents

Abstract

FIELD: agriculture.

SUBSTANCE: invention is intended for agriculture, food industry, solar industry and electronics industry and can be used in manufacture of film-covering materials, packaging, fluorescent screens and displays. Fluorescent polymeric film produced by co-extrusion. First extruder hopper is purged for at least 20 minutes with nitrogen or an inert gas at a flow rate of at least 5 l/min, followed by metering and loading into extruder hopper thermoplastic polymer with quantum dots, introduced in its volume, and thermoplastic resin of same grade used to make additional film layer. Melting temperature in extruder is set no higher than 180°C. Quantum dots used are colloidal semiconductor materials selected from a group consisting of CdSe, CdS, CdTe, InP, InAs, CuInS₂, CuInSe₂, ZnS, CdZnS, CdZnSe. To improve flowability of polymer 0.1÷2.0 wt% rheological modifier can be used. To improve transparency of film, a nucleator can be used in an amount of not more than 2.0 wt%. To reduce intensity of oxidation processes, additive-based phenolic compounds and organic phosphites can be used. To lower melting temperature 0.1÷2.0 wt% additive can be used.

EFFECT: higher efficiency of luminescence, improved mechanical properties of film.

9 cl, 2 dwg, 12 ex

Description

The invention relates to the production of multilayer film polymeric materials based on thermoplastic polymers, namely to fluorescent polymer films that selectively absorb radiation. This type of film materials are used in agriculture as light-correcting film covering materials, special packaging materials, materials for the transformation of natural solar radiation in solar energy, for the production of fluorescent screens and displays.

The introduction of fluorescent components into the volume of a thermoplastic material is usually associated with a deterioration in the mechanical and optical properties of the film. Compensation for the deterioration of the properties of fluorescent films is most often achieved by the introduction of various additives.

A known method of manufacturing a film material (US patent No. 6153665) using a phosphor based on yttrium oxysulfide activated by europium, and polyaminosuccinate as a light stabilizer. The resulting light-correcting material effectively converts the wavelengths of sunlight into the long-wavelength region. According to the authors, a synergistic effect, consisting in the combined action of a phosphor and a stabilizing additive, plays a special role here. A slight increase in the shelf life and mechanical properties of the material is noted.

A known method of extrusion manufacturing of a polyethylene film (as USSR USSR No. 1780309). To obtain fluorescent films based on high-pressure polyethylene (LDPE), it is proposed to use complex compounds of europium nitrate with 1,10-phenanthroline, or 2,2′-dipyridyl, or 4,4′-dimethyl-2,2′- as light-converting additives dipyridyl mixed with paraffin. The use of paraffin increases the dispersion and uniformity of the distribution of the particles of the light transducer in the film, increases the stability of light-transforming properties under conditions of moisture and heat. Films obtained on the basis of this composition provide good light conversion, however, they exhibit low photostability and a short shelf life.

A common disadvantage for this type of material is the inefficient use of the near infrared range; low photostability, significantly limiting the useful life of the material.

Preliminary studies show the high efficiency of using quantum dots as fluorescent components based on cadmium, lead, indium sulfides, selenides and chalcogenides; selenides of these metals containing a phase or shell, or one or more layers of zinc and cadmium sulfide or other semiconductor materials, characterized by a band gap different from the main material and effectively luminescent in the spectral region of 580-700 nm.

The introduction of quantum dots into a thermoplastic polymer also involves the use of various additives designed both to compensate for changes in the mechanical and optical properties of the film and to impart new properties associated with the presence of these phosphors. In addition, an important role in achieving a positive result is played by the nature and properties of the thermoplastic used, related to their compatibility with quantum dots, processing temperatures, melt indices, glass transition and melting temperatures, possibly with oxygen permeability, peroxidation ability, dispersion and crystallinity.

The objective of the invention is to create a method of manufacturing a fluorescent film, providing increased light conversion efficiency, increasing the service life of the produced film, its durability.

The technical result consists in increasing the efficiency of luminescence, as well as improving the mechanical properties of the film.

The problem is solved in that in the method of manufacturing a fluorescent polymer film, which consists in dosing and loading a thermoplastic polymer and a material containing a fluorescent component into the extruder hopper and manufacturing a film, according to the invention, a related thermoplastic polymer with quantum dots is used as the material containing the fluorescent component, introduced into its volume, and before the manufacture of the film, the extruder hopper is purged with a non-oxidizing gas medium.

Preferably, the hopper is purged for at least 20 minutes with a non-oxidizing gas flow of at least 5 l / min. In this case, an inert gas or nitrogen is used as a non-oxidizing gas medium.

It is advisable to load into the hopper a thermoplastic polymer and a material containing a fluorescent component in a ratio of from 100: 1 to 10: 1 parts by weight.

It is also advisable to set the melting temperature of the polymer not higher than 180 ° C, and to reduce the processing temperature of the polymer to use an additive that reduces the melting temperature in an amount of 0.1-2.0 wt.%. Moreover, to increase the fluidity of the polymer, it is preferable to use a re-modifier in an amount of 0.1-2.0 wt.%, And to increase the transparency of the film, use a nucleator in an amount of not more than 2.0 wt.%. Moreover, to reduce the intensity of oxidative processes, it is desirable to use an additive based on phenol-containing compounds and organic phosphites.

In a preferred embodiment, the film is produced by coextrusion to form a fluorescent layer and at least one additional layer, and semiconductor colloidal materials selected from the groups CdSe, CdS, CdTe, InP, InAs, CuInS ₂ , CuInSe ₂ are used as quantum dots , ZnS, CdS, CdZnS, CdZnSe. In this case, as a thermoplastic polymer for the manufacture of an additional layer, it is desirable to use a polymer having higher mechanical properties with respect to the polymer with quantum dots.

In another preferred embodiment, the film is produced with the formation of two additional layers and a fluorescent layer placed between them, and to increase the compatibility of semiconductor materials in the fluorescent layer, N, N′-alkyl derivatives of 4-aminopyridine, trioctylphosphine, stearic and oleic acids, thioglycolic acid are used, Quaternary ammonium bases, aliphatic amines and aliphatic thioalcohols.

The invention is explained in detail below with reference to the drawings, in which Fig. 1 shows the integrated intensity of the average daily illumination in a greenhouse; figure 2 shows the data of the mechanical and fluorescent properties of various samples of the film.

A method of manufacturing a fluorescent polymer film consists in dispensing and loading a thermoplastic polymer and a material containing a fluorescent component into an extruder hopper. As a material containing a fluorescent component, a related thermoplastic polymer with quantum dots introduced into its volume is used. To increase the efficiency of luminescence before the manufacture of the film, the hopper is purged with a non-oxidizing gas medium.

An inert gas or nitrogen is used as a non-oxidizing gas medium. The hopper is purged for at least 20 minutes with a gas flow rate of at least 5 l / min. The optimum purge time range is from 30 to 60 minutes. The purge procedure significantly reduces the probability of destruction of quantum dots and increases the efficiency of luminescence.

Figure 1 shows the integrated intensity of the average daily illumination at the latitude of Moscow in the greenhouse for months: 1 - March, 2 - April, 3 - May, 4 - June, 5 - July, 6 - August, 7 - September. Numeral 1 denotes a curve showing data for a non-fluorescent polyethylene film (control experiment); number 2 - data for a fluorescent film produced without blowing the feed hopper with inert gas; number 2 - data for a film produced with a hopper flushing with an inert gas. Illumination measurements were carried out using a TDK-VD spectrocolorimeter. To obtain the film, LDPE grades 15803-020 and 10803-020 were used. The data presented show that flushing the hopper with an inert gas increases the integrated light intensity by 20-40 units.

The film is produced by extrusion, while the thermoplastic polymer and the material containing the fluorescent component are loaded into the hopper of the extruder in a ratio of 100: 1 to 10: 1 parts by weight. The melting temperature of the polymer is set no higher than 180 ° C. In this case, the wall temperature of the extruder in the feed zone is set to not more than 80-100 ° C, and the wall temperature in the melting zone is set to not more than 150-180 ° C. A higher temperature in the melting zone is undesirable since can lead to the degradation of quantum dots due to their oxidation. The wall temperature in the metering zone is 220-235 ° C.

As fluorescent colloidal materials (see Nanocrystal quantum dots./Second Edition. Edited by Victor Klimov. USA, 2004), quantum dots based on cadmium, lead, and indium sulfides, selenides, and chalcogenides are used to create fluorescent layers; selenides of these metals containing a phase or shell, or one or more layers of zinc and cadmium sulfide or other semiconductor materials, characterized by a band gap different from the main material and effectively luminescent in the spectral region of 580-700 nm. The concentration of the luminescent material in the fluorescent layers is 0.01-1.0 wt.%.

It is possible to lower the polymer processing temperature using an additive, for example AMF 705 (Made in Germany), which reduces the melting temperature in an amount of 0.1-2.0 wt.%. To increase the fluidity of the polymer, it is desirable to use a re-modifier, for example SMD 7.5, in an amount of 0.1 ÷ 2.0 wt.%. To increase the transparency of the film, it is desirable to use a nucleator, for example NU 510, in an amount of not more than 2.0 wt.%, And to reduce the intensity of oxidative processes, an additive based on phenol-containing compounds and organic phosphites, for example AO 25.

A multilayer fluorescent material may contain two or more polymer layers of different thicknesses. For the manufacture of multilayer fluorescent materials, coextrusion methods can be used on standard equipment equipped with one or more extruders operating under various conditions and with various technological parameters. The thickness of the manufactured layers is 10 ÷ 100 microns.

Extrusion heads for manufacturing a multilayer tubular film are different from those for manufacturing a single layer tubular film. The main difference is that the central mandrel is surrounded coaxially by several annular elements, between which there are annular slots. These ring elements are connected to one or more extruders for feeding the polymer melt (German patents No. 19924540, No. 2306834). In some cases, the annular gaps can be conical and can be located one above the other (European patent No. 1055504). In heads of any type, the melt is divided by means of primary distributors into several streams, which are then sent to spiral distributors, which ensure the union of all streams. The head is equipped with the necessary number of feeders supplying polymer from extruders, each operating in its own mode.

The film is produced by coextrusion with the formation of a fluorescent layer and at least one additional layer. Moreover, as a thermoplastic polymer for the manufacture of an additional layer using a polymer with higher mechanical properties with respect to the polymer with quantum dots. As quantum dots, as already mentioned, semiconductor colloidal materials selected from the group of CdSe, CdS, CdTe, InP, InAs, CuInS ₂ , CuInSe ₂ , ZnS, CdS, CdZnS, CdZnSe are used.

The best result can be obtained if the film is produced with the formation of two additional layers and a fluorescent layer placed between them. At the same time, to increase the compatibility of semiconductor materials in the fluorescent layer, N, N′-alkyl derivatives of 4-aminopyridine, trioctylphosphine, stearic and oleic acids, thioglycolic acid, quaternary ammonium bases, aliphatic amines and aliphatic thioalcohols are used.

As thermoplastic polymers for luminescent and non-luminescent (additional) film layers, it is proposed to use: low and high pressure polyethylene (PE) (HDPE and HDPE), a mixture of HDPE and HDPE, polypropylene (PP) and its mixture with PE, polybutadiene (PB) and its copolymers and its mixtures with PE and PP, polystyrene (PS) and its copolymers, polybutylene and its copolymers, copolymers of PB and ethylene, poly-4-methylpentene-1 and its copolymers, copolymers of ethylene with vinyl acetate, copolymers of ethylene with vinyl alcohol, copolymers of ethylene with acrylic and metacre silic acid, polyvinylpyrrolidone, polyvinylpyridine. An organosilicon polymer of polydimethylsiloxane, polydiphenylsiloxane and mixtures thereof with melting points of 75 ÷ 110 ° C can be used.

For the preparation of fluorescent layers, polymers and copolymers with low mechanical properties, but characterized by a high degree of compatibility with quantum dots and the necessary additives and modifiers, were used.

The introduction of fluorescent components into the volume of a thermoplastic material is usually associated with a deterioration in the mechanical and optical properties of the film. So, a LDPE film with a thickness of 100 μm, made of a polymer of grades 15803-020 and 10803-020, not containing the fluorescent additives mentioned above, is characterized by the following physical and mechanical properties: tensile strength 150 kg / m ² , elongation at break 350%. A fluorescent film obtained from polyethylene of the same grades with the introduction of 0.1% quantum dots, with the addition of appropriate light stabilizers, antioxidants and rheomodifiers, has the following characteristics: tensile strength 130 kg / m ² , elongation at break 280%, i.e. values smaller than stipulated by GOST 10354-82.

At the same time, a composite three-layer fluorescent film consisting of two layers of HDPE grades 273-83, 276-73, 277-73 with a thickness of 30 μm and the above-described fluorescent layer based on LDPE also with a thickness of 30 μm has the following mechanical characteristics: strength 200 kg / m ² and elongation of 450%. That is, while maintaining the luminescent properties, the mechanical properties of such a film are significantly better than the initial LDPE of these grades.

Similarly, polymers that are not used at all to produce film materials can be used to create the luminescent layer.

There are a number of polymer media in which quantum dots exhibit enhanced photostability, high quantum fluorescence yield, and a stable spectral distribution of luminescence. For example, the quantum yield of fluorescence in a matrix of polystyrene, polyvinylpyridine, polypropylene, a copolymer of vinyl acetate, acrylic, methacrylic acid and some others is significantly higher than in matrices of polyvinyl chloride, polyvinylidene chloride, fluorine-containing copolymers that effectively quench fluorescence.

As the outer (additional) layers of the multilayer film, it is preferable to use polyolefins from a number of LDPE, HDPE, PP and its copolymers, polyisobutylene. These layers provide effective protection of the inner layers from moisture. Such protection is necessary due to the fact that water molecules are effective quenchers of fluorescence of quantum dots.

As the fluorescent layers, film-forming thermoplastic polymers are used in the following ratio of components, wt.%:

- fluorescent component - 0.05 ÷ 1.0;

- surfactant additives to improve compatibility - up to 1.0;

- additives to improve processability (extrusion) - up to 2.0;

- additives to improve transparency - up to 2.0;

- possibly antioxidants - up to 2.0;

- possibly photostabilizers - up to 1.0;

- possible diffusers SiO ₂ , TiO ₂ , ZnO.

- the necessary polymer or mixture of polymers - the rest.

In the case of using polymers poorly compatible with polyolefin layers, it is possible to use gluing (cementing) layers that act as adhesives that do not contain a solvent based on polyamides and EVON.

The manufacture of a multilayer film is carried out by coextrusion followed by blowing or calendering.

The following are examples of the implementation of the invention.

Example 1. To obtain a light-correcting covering film, HDPE grades 15803-020 and 10803-020 were used with a density of 0.918-0.019 g / cm ² , elongation at break of 580%, tensile strength of 120 kg / m ² . A superconcentrate obtained in accordance with the developed technology using CANdots quantum dots (CAS N1306-23-7, quantum dots with a CdSe core and ZnSe / ZnS shell, dispersion in hexane, maximum luminescence peak was used to fabricate a single-layer fluorescent film by blowing the sleeve. at 620 nm, manufacturer Strem Chemicals Inc).

To obtain a superconcentrate in a dissolver for mixing were loaded:

10 kg of a suitable solvent selected from p-, o- or m-xylene, cresol, turpentine, hexanone, hexane, octane, decane, toluene, methyl cellosolve, pyridine, acetone, ethanol, methanol, butanol, allyl acetate;

- 2.0 kg of LDPE (GOST 16337-77, manufactured by Kazanorgsintez JSC);

- 20.0 g of paraffin hydrocarbons;

- 2.0 g of light stabilizer;

- 2.0 g of plasticizer;

- 20.0 g of colloidal phosphor based on CANdots quantum dots (CAS N1306-23-7, quantum dots with a CdSe core and ZnSe / ZnS shell, dispersion in hexane, maximum luminescence peak at 620 nm, manufacturer Strem Chemicals Inc) .

Mixing is carried out for 2 hours at a temperature of 60-80 ° C. Upon achievement of complete dissolution, a precipitant from the above series is added to the mixture and the temperature drops to 35-45 ° C. As precipitation occurs, the precipitate is discharged onto the tape dryer, where the bulk of the solvent is blown off with warm air. The blow-off solvent is captured and returned back to the dissolver. From the conveyor belt dryer polymer flakes are unloaded into the hopper of the grinder.

The resulting material is a superconcentrate (a material containing a fluorescent component), which is used for the production of film material. The input rate of the superconcentrate was 1:15.

As a result, after the extruder hopper was flushed with inert gas for 30 minutes at a flow rate of 7 l / min and the melt was blown (extrusion), a fluorescent film with a thickness of 90 μm was obtained, with a tensile strength of 110 kg / m ² and an elongation at break of 220%.

The absolute quantum yield of luminescence of the obtained material, measured by a known method, was 47% (see Galanin MD and others. Measurement of the quantum yield of photoluminescence of dye solutions by the method of an integrating sphere. Optics and spectroscopy. 1982. V.53. S.684- 685).

Example 2. A single-layer fluorescent film was made according to example 1, characterized in that in addition to these components the following additives were used: AMF 705 - to reduce the processing temperature (extrusion), 1.0% wt., AO 25 - antioxidant, 0.5% wt., Akkat PE / F101170 - UV stabilizer - 1.0% wt. The superconcentrate of Example 1 was used to blow the sleeve. The obtained fluorescent film had the following properties: thickness 90 μm, tensile strength 60 kg / m ² , elongation 200%. The quantum yield of luminescence is 41%.

Example 3. A coextrusion method was used to produce a three-layer fluorescent film containing two outer (additional) layers of HDPE with a relative elongation at break of 500%, tensile strength of 100 kg / m ² , and a thickness of 30 μm. For the central (fluorescent) layer, also 30 μm thick, the LDPE according to Example 2 was used with the difference that the ratio of granules of the superconcentrate and polymer was 1: 7.5.

Example 4. A three-layer fluorescent film according to claim 3 was made, characterized in that PP 21030-16N grade polypropylene was used as the outer layers.

Example 5. A three-layer fluorescent film was made, characterized in that LDPE was used as two external non-fluorescent layers, and polystyrene containing quantum dots in an amount of 0.1 wt% was used for the central fluorescent layer.

Example 6. A three-layer fluorescent film was made, characterized in that HDPE was used to produce external non-fluorescent layers, and a copolymer of ethylene and vinyl acetate containing 70% ethylene and 30 vinyl acetate units was used for the central fluorescent layer.

Example 7. A three-layer fluorescent film was produced, characterized in that for the central fluorescent layer a polymer mixture containing 90% polystyrene and 10% polyvinylpyridane was used.

Example 8. A three-layer fluorescent film was made, characterized in that polyvinylpyridane was used for the central fluorescent layer.

Example 9. A three-layer fluorescent film was made, characterized in that for the central fluorescent layer a copolymer of ethylene and methacrylic acid containing 75% ethylene units and 25% methacrylic acid units was used.

Example 10. A three-layer fluorescent film was produced, characterized in that for the central fluorescent layer a copolymer of ethylene and vinylpyrrolidone containing 60% units of ethylene and 40 vinylpyrrolidone was used.

Example 11. A three-layer fluorescent film was made, characterized in that polyvinylpyrrolidone was used for the central fluorescent layer.

Example 12. A five-layer fluorescent film was made consisting of three non-fluorescent layers of LDPE and two fluorescent layers consisting of polyphenylsiloxane with a melting point of 95 ° C. Fluorescent layers (second and fourth layers) are placed between the non-fluorescent layers (first, third and fifth layers). The layer thickness was 20 μm.

The results on the optical and mechanical properties of the proposed materials are summarized in the table (see figure 2). The tensile strength was measured according to ASTM D-882, Method A. The elongation was measured according to FSTM D-882. Method A. It can be seen from the table that multilayer films obtained by combining layers of different polymers can not only compensate for the deterioration of the mechanical properties of polyolefins, but also improve them compared to the original film. The parameters for the materials obtained are within the boundaries prescribed by GOST 10354-82 for films used as covering material. The use of a number of polymers with enhanced compatibility also made it possible to achieve higher values of the quantum yields of photofluorescence.

Claims (9)

1. A method of manufacturing a fluorescent polymer film, characterized in that the film is produced by coextrusion to form a fluorescent layer and at least one additional layer, for which a thermoplastic quantum dot polymer used to make the fluorescent film layer is dosed and loaded into the hopper of the extruder introduced into its volume, and selected from the same class of thermoplastic polymers, thermoplastic polymer, which is used for the manufacture of additional layer of the film, while before the film is made, the extruder hopper is purged with a non-oxidizing gas medium, a thermoplastic polymer is used to produce an additional layer, which provides higher mechanical properties of the film in terms of tensile strength and elongation relative to a thermoplastic polymer with quantum dots, and the melting temperature in the extruder set no higher than 180 ° C. 2. The method according to p. 1, characterized in that they use an additive that reduces the melting temperature of the thermoplastic polymer in an amount of 0.1 ÷ 2.0 wt.%. 3. The method according to p. 1 or 2, characterized in that the hopper is purged for at least 20 minutes at a flow rate of non-oxidizing gas medium of at least 5 l / min. 4. The method according to p. 3, characterized in that inert gas or nitrogen is used as a non-oxidizing gas medium. 5. The method according to p. 3, characterized in that to increase the fluidity of the polymer using rheomodifier in an amount of 0.1 ÷ 2.0 wt.%. 6. The method according to p. 3, characterized in that to increase the transparency of the film using a nucleator in an amount of not more than 2.0 wt.%. 7. The method according to p. 3, characterized in that to reduce the intensity of oxidative processes using an additive based on phenol-containing compounds and organic phosphites. 8. The method according to p. 3, characterized in that the quantum dots use semiconductor colloidal materials selected from the group comprising CdSe, CdS, CdTe, InP, InAs, CuInS ₂ , CuInSe ₂ , ZnS, CdZnS, CdZnSe. 9. The method according to p. 8, characterized in that the manufacture of the film is carried out with the formation of two additional layers and placed between them fluorescent layer.

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