TRANSPARENT POLYMER FILM WITH DISCOLOURATION COMPENSATION

Abstract

A single-layer or multilayer film formed from one or more polymeric materials has CIE colour values a* and b* such that −7≤a*≤0, −15≤b*≤0 and an optical transmission T such that 60%≤T≤95%. The inventive, transparent films provide discoloration compensation that alleviates yellowing caused by UV light.

Claims

1. Single-layer or multilayer transparent film comprising one or more polymeric materials, wherein the film has CIE colour values a* and b* of −7≤a*≤0, −15≤b*≤0 and an optical transmission T of 60%≤T≤95%.

2. The film according to claim 1, wherein −7≤a*≤−5, −6≤a*≤−4, −5≤a*≤−3, −4≤a*≤−2, −3≤a*≤−1 or −2≤a*≤0.

3. The film according to claim 1, wherein −15≤b*≤−11, −13≤b*≤−9, −11≤b*≤−7, −9≤b*≤−5, −7≤b*≤−3, −5≤b*≤−1 or −3≤b*≤−0.

4. The film according to claim 1, wherein the film has an optical transmission T of 65%≤T≤95%, 70%≤T≤95%, 75%≤T≤95%, 80%≤T≤95%, 85%≤T≤95% or 90%≤T≤95%.

5. The film according to claim 1, wherein said film contains one or more main dyes which absorb light having wavelengths in a range from 520 to 600 nm.

6. The film according to claim 1, wherein said film contains one or more supplementary dyes which absorb light having wavelengths in range from 520 to 600 nm, where the main and supplementary dyes are present in a ratio of the integrated absorption of the one or more main dyes in the wavelength range from 520 to 600 nm to integrated absorption of the one or more supplementary dyes in the wavelength range from 520 to 600 nm is in the range from 4:1 to 1:1.

7. The film according to claim 1, wherein the film comprises one or more layers which, independently of one another, consist of a polymeric material having a proportion of from 60 to 99% by weight of vinyl chloride polymer (VCP), based on the total weight of the layer.

8. The film according to claim 1, wherein the film comprises one or more layers which, independently of one another, consist of a polymeric material having a proportion of from 60 to 99% by weight of polyvinylidene chloride (PVdC), based on the total weight of the layer.

9. A blister film comprising the film according to claim 1.

10. A process for producing the single-layer or multilayer transparent film according to claim 1 comprised of one or more polymeric materials formed in one or more film plants, said process comprising the steps: (a) providing one or more polymeric materials; (b) providing one or more dyes; (c) mixing of the one or more dyes with one or more of the polymeric materials in predetermined proportions; (d) plasticizing the one or more polymeric materials in one or more gelling apparatuses; and (e) shaping one or more polymeric materials into the film by extruding, coextruding, calendering, coating, extrusion coating and/or laminating; wherein the one or more dyes are added in such proportions that the film has CIE colour values a* and b* of −7≤a*≤0, −15≤b*≤0 and an optical transmission T of 60%≤T≤95%.

Description

[0158] The invention will be illustrated below with the aid of drawings and examples. The drawings show

[0159] FIG. 1 a schematic sectional view of a film having four layers and two bonding layers;

[0160] FIG. 2 transmission spectra of a film before and after UV irradiation in an irradiation chamber;

[0161] FIG. 3 absorbance of a film caused by UV irradiation, presented as absorption coefficient or optical density;

[0162] FIG. 4 absorption coefficients of an ideal dye according to the invention and also two commercial dyes;

[0163] FIG. 5 a schematic depiction of the instrumental and visual colour measurement or perception;

[0164] FIG. 6 the curve of a function F.sub.a(λ) for the empirical calculation of the colour change Δa*;

[0165] FIG. 7 the curve of a function F.sub.b(λ) for the empirical calculation of the colour change Δb*;

[0166] FIG. 8-10 absorption coefficients of the dyes #1 to #9;

[0167] FIG. 11-13 optical densities of illustrative films.

[0168] FIG. 1 shows a schematic sectional view of a film 1 according to the invention having four layers 2, 3, 4, 5 and two bonding layers 6, 7 which are arranged between the layers 2 and 3 and between the layers 4 and 5. The bonding layers 6, 7 serve to adhesively bond the layers 2 and 3 or 4 and 5. The film 1 is transparent and has an optical transmission of from 60 to 95%. One or more of the layers 2, 3, 4, 5 and bonding layers 6, 7 contain one or more dyes. The one or more dyes and the respective amount or mass thereof is selected in such a way that the film 1 has CIE colour values a* and b* such that −7≤a*≤0, −15≤b*≤0. The CIE colour values a* and b* are determined in accordance with DIN EN ISO 11664-1:2011-07, DIN EN ISO 11664-2:2011-07 and DIN EN ISO 11664-3:2013-08 using standard light CIE D65, 10° field of view and tristimulus curves x, y, z of the CIE standard valence system of 1931.

[0169] The thickness of the bonding layers 6, 7 is a factor of from 6 to 1000 smaller than the thickness of the layers 2, 3, 4, 5. Accordingly, the contribution of the bonding layers to the total weight of the film 1 and their barriers towards oxygen and water vapour is negligible. Apart from establishing an adhesive bond between adjacent layers, the bonding layers 6, 7 can also function as carriers for one or more dyes.

[0170] FIG. 2 shows the spectral transmission of a film according to the invention in the original state (t=0 min) and after UV irradiation for 120 minutes (t=120 min) in an irradiation chamber. In a wavelength range from about 400 to 600 nm, the irradiated film has a significantly reduced transmission or increased absorption compared to the unirradiated film. FIG. 3 shows the absorption coefficient determined from the transmission curves depicted in FIG. 2 as a function of the wavelength. In a wavelength range from about 430 to 440 nm, which overlaps with the range of violet light (400 to 450 nm), the absorption coefficient displays a maximum. The colour complementary to this wavelength range is yellow-green (cf. https://de.wikipedia.org/wiki/Kompiementärfarbe). In the range of visible light from 380 to 780 nm, i.e. without taking into account wavelengths of <380 nm, the greatest absorption (by area) is at 495.5 nm between blue and cyan. The complementary colour corresponding thereto is orange. This result is in agreement with the observation of an initially yellowish discolouration of the film which changes to brownish with increasing UV dose.

[0171] Based on the above-described colour measurements on UV-weathered films and mathematical analyses, the inventors have postulated an “ideal” dye which compensates a “representative yellowing” of a film. In the context of the present invention, the term “representative” relates to a UV dose to which a film is subjected under normal use conditions. The representative UV dose corresponds to 360 KJ.Math.m.sup.−2 at a black standard temperature (BST) of 65° C. in accordance with DIN EN ISO 4892-2: 2013-06 B2. The irradiation of the films with the representative UV dose was carried out in a Suntest XLS+ instrument from Atlas Material Testing Technology GmbH.

[0172] The form or curve of the absorption coefficient of the “ideal” dye is shown in the graph of FIG. 4 as a function of the wavelength and corresponds to a Gaussian curve having a centre at 577 nm and full width at half maximum (FWHM) of 20 nm. At an appropriately selected content or optical density of the ideal dye, a film having CIE colour values a* and b* such that −7≤a*≤0, −15≤b*≤0 is obtained.

[0173] Furthermore, the absorption coefficient of the dye epolight 5819 from Epolin and of Cu-phthalocyanine are shown in FIG. 4. Surprisingly, the same CIE colour values a* and b* as in the case of the “ideal” dye are obtained by means of combination of the dyes epolight 5819 and Cu-phthalocyanine having a relatively low optical density under identical conditions, i.e. in films having the same nature and thickness. It should be rioted here that the scaling of the optical densities of epolight 5819 and Cu-phthalocyanine is increased by a factor of 2 relative to the “ideal” dye in the graph of FIG. 4.

[0174] FIG. 5 schematically shows the measurement of the CIE colour values a* and b* of a film 12 according to the invention by means of a spectrophotometric colorimeter 15. For this purpose, the film 12 is arranged or laid on a certified white scattering standard 14. The white scattering standard 14 consists of BaSO.sub.4 or Spectralon® (sintered polytetrafluoroethylene) and corresponds to a virtually ideal Lambert reflector. The light used for the colour measurement is produced by a light source 10 conforming to CIE D65 or by a light source 10 having a known spectral intensity distribution 11. If the spectral intensity distribution 11 of the light source is not known, it is determined by means of a spectrophotometer (or spectrophotometric colorimeter). In the software-aided evaluation, the spectra recorded using the colorimeter are converted into spectra conforming to CIE 65 by multiplication by a wavelength-dependent factor K(λ) which corresponds to the intensity ratio of a CIE 65 standard light source and the light source actually used, i.e.

[00007]$K\left(\lambda \right)=\frac{I\left(\mathrm{ClE}65;\lambda \right)}{I\left(\mathrm{light}\mathrm{source};\lambda \right)}.$

[0175] The light emitted by the light source 10 impinges on the film 12, passes through the latter for a first time, is diffusely reflected by the white scattering standard 14, passes through the film 12 a second time and is detected in the colorimeter 15. The calorimeter 15 comprises a spectrophotometer having a wavelength-dispersive optical element, in particular a grating, and a photodiode array. The diffusely reflected light from the film 12 is collected in combination with the white scattering standard 14 from a solid angle range having a conical opening angle of 10° and bundled onto the entry slit of the spectrophotometer.

[0176] The light emitted by the light source 10 is more or less strongly absorbed or attenuated as a function of the wavelength during the double passage through the film 12. The attenuation of the light in the film 12 is described mathematically by a wavelength-dependent transmission 13. For light quanta (photons), the film 12 represents a transmission filter having a wavelength-dependent transmission probability.

[0177] The spectrum recorded in the colorimeter 15 for the light reflected from the film 12 and the white scattering standard 14 is finally multiplied or convolved with tristimulus curves x, y, z of the CIE standard valence system of 1931 (reference 16 in FIG. 5) in order to calculate CE colour values X, Y, Z and a*, b*. The tristimulus curves x, y, z take into account the spectral sensitivities or actuation probabilities of the photoreceptors in the retina of the human eye (https://de.wikipedia.org/wiki/CIE-Normvalenzsystem).

[0178] FIG. 8 to 10 show the optical densities E(λ) or absorption coefficients α(λ) of the dyes #1 to #9 in standardized units as a function of the wavelength in the visible range from 380 to 780 nm. Numerical values corresponding thereto are shown in Table 2.

TABLE-US-00002 TABLE 2 λ [nm] #1 #2 #3 #4 #5 #6 #7 #8 #9 380 0.00 0.00 0.00 0.00 0.00 0.11 0.08 0.15 0.51 385 0.00 0.00 0.00 0.00 0.00 0.10 0.07 0.12 0.45 390 0.00 0.00 0.00 0.00 0.00 0.10 0.06 0.11 0.39 395 0.00 0.00 0.00 0.00 0.00 0.09 0.05 0.09 0.34 400 0.00 0.00 0.00 0.00 0.00 0.08 0.05 0.08 0.29 405 0.03 0.02 0.05 0.02 0.00 0.07 0.04 0.07 0.26 410 0.02 0.02 0.05 0.02 0.00 0.06 0.03 0.06 0.23 415 0.02 0.02 0.04 0.02 0.00 0.05 0.03 0.05 0.21 420 0.01 0.02 0.04 0.02 0.00 0.05 0.02 0.04 0.19 425 0.01 0.02 0.04 0.02 0.00 0.04 0.02 0.03 0.18 430 0.01 0.03 0.04 0.02 0.00 0.04 0.01 0.02 0.16 435 0.01 0.04 0.04 0.02 0.00 0.04 0.01 0.02 0.14 440 0.00 0.06 0.04 0.02 0.00 0.04 0.01 0.01 0.13 445 0.00 0.07 0.04 0.02 0.00 0.04 0.01 0.01 0.11 450 0.00 0.09 0.04 0.02 0.00 0.04 0.00 0.01 0.10 455 0.01 0.11 0.04 0.03 0.01 0.05 0.00 0.01 0.09 460 0.01 0.14 0.03 0.03 0.03 0.05 0.00 0.01 0.09 465 0.01 0.17 0.04 0.04 0.04 0.05 0.00 0.01 0.08 470 0.01 0.21 0.03 0.05 0.06 0.05 0.00 0.00 0.08 475 0.01 0.24 0.03 0.07 0.10 0.05 0.00 0.00 0.08 480 0.01 0.28 0.04 0.08 0.15 0.06 0.00 0.00 0.08 485 0.01 0.32 0.04 0.11 0.23 0.06 0.01 0.01 0.08 490 0.01 0.38 0.05 0.14 0.28 0.07 0.01 0.01 0.09 495 0.02 0.45 0.05 0.18 0.31 0.08 0.01 0.01 0.09 500 0.02 0.52 0.06 0.24 0.34 0.09 0.01 0.01 0.10 505 0.03 0.57 0.07 0.30 0.40 0.10 0.02 0.01 0.11 510 0.03 0.61 0.09 0.34 0.52 0.11 0.03 0.02 0.12 515 0.04 0.64 0.10 0.37 0.69 0.13 0.03 0.02 0.14 520 0.05 0.69 0.13 0.41 0.88 0.15 0.04 0.03 0.17 525 0.07 0.76 0.20 0.49 0.98 0.18 0.05 0.03 0.20 530 0.12 0.85 0.22 0.61 0.98 0.22 0.06 0.04 0.24 535 0.16 0.94 0.20 0.78 0.79 0.25 0.09 0.04 0.29 540 0.14 0.99 0.19 0.92 0.56 0.27 0.13 0.06 0.35 545 0.13 0.99 0.20 0.99 0.33 0.27 0.16 0.09 0.42 550 0.14 0.93 0.24 0.98 0.16 0.29 0.15 0.13 0.51 555 0.15 0.86 0.30 0.85 0.07 0.33 0.14 0.15 0.60 560 0.17 0.81 0.35 0.60 0.02 0.40 0.15 0.14 0.70 565 0.21 0.80 0.46 0.37 0.00 0.48 0.17 0.13 0.78 570 0.31 0.84 0.74 0.22 0.00 0.57 0.19 0.14 0.85 575 0.54 0.89 0.98 0.11 0.00 0.71 0.22 0.15 0.91 580 0.90 0.92 0.92 0.05 0.00 0.91 0.33 0.16 0.97 585 0.99 0.88 0.58 0.02 0.00 1.00 0.57 0.19 0.99 590 0.72 0.75 0.26 0.01 0.00 0.90 0.92 0.28 1.00 595 0.37 0.57 0.11 0.00 0.00 0.61 0.98 0.49 0.99 600 0.16 0.38 0.05 0.00 0.00 0.34 0.71 0.84 0.98 605 0.06 0.24 0.03 0.00 0.00 0.19 0.40 1.00 0.97 610 0.04 0.13 0.02 0.00 0.00 0.09 0.19 0.75 0.96 615 0.02 0.07 0.01 0.00 0.00 0.05 0.10 0.41 0.94 620 0.02 0.04 0.01 0.00 0.00 0.03 0.05 0.18 0.92 625 0.01 0.02 0.01 0.00 0.00 0.01 0.03 0.09 0.90 630 0.01 0.01 0.01 0.00 0.00 0.01 0.02 0.05 0.86 635 0.01 0.00 0.01 0.00 0.00 0.00 0.02 0.03 0.83 640 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.02 0.79 645 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.02 0.75 650 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.72 655 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.69 660 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.67 665 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.66 670 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.66 675 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.67 680 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.68 685 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.70 690 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.71 695 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.72 700 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.71 705 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.71 710 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.69 715 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.67 720 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.65 725 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.62 730 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.60 735 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.56 740 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.53 745 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.49 750 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.45 755 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.41 760 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.37 765 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.34 770 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.31 775 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.28 780 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.26

EXAMPLES 1 TO 24

[0179] A total of 25 multilayer films, hereinafter designated as Example 1 to 24 and Comparative Example 25, having a layer structure of the type 250 μm of PVC/30 μm of PE/71 μm of PVdC were produced. For this purpose, base films of PVC material comprising 92% by weight of PVC, from 6 to 8% by weight of customary industrial additives, e.g. thermal stabilizer, lubricant and impact modifier, and from 0 to 2% by weight of two colouring additives were firstly manufactured by means of a laboratory calendar. The thickness of the PVC films was in each case 250 μm. A total of from 0.01 to 2% by weight of two colouring additives, each containing a dye of the type #1 to #20 as per Table 1, were added to the PVC materials of Examples 1 to 24. The proportion by weight of each colouring additive was indicated by the manufacturer or established by the inventors by means of the measured optical density or absorption coefficient of the respective dye. No colouring additive was added to the PVC material of Comparative Example 25. A 30 μm thick PE film was laminated onto each of the PVC films of Examples 1 to 24 and of Comparative Example 25. The PE layer was subsequently coated with an aqueous PVdC dispersion in each of a number of passes and the coating was dried in order to obtain an integral PVdC layer having a total weight per unit area of 120 g/m.sup.2 (corresponding to a thickness of 71 μm).

[0180] For each of the films of Examples 1 to 24 and the Comparative Example 25, a transmission spectrum Ta(λ) where n=1, . . . , 25 was recorded using a spectrophotometer and the colour values a* and b* were determined using a spectrophotometric colorimeter. The total optical density E.sub.m(λ) was determined from the natural logarithm of the ratio T.sub.m(λ)/T.sub.25(λ) of the transmission spectra T.sub.m(λ), m=1, . . . , 24 of Examples 1 to 24 and of Comparative Example 25 according to the relationship

[00008]$E_m\left(\lambda \right)=\ln \left(\frac{T_m\left(\lambda \right)}{T_{25}\left(\lambda \right)}\right).$

[0181] The total optical density E.sub.m(λ) calculated in this way is in agreement with the sum of the optical densities of the two dyes weighted according to the established proportions by weight of the colouring additives.

[0182] The colour values a*, b*, the optical transmission and also further data of Examples 1 to 24 and of Comparative Example 25 are shown in Table 3.

TABLE-US-00003 TABLE 3 Optical Example Main Supplementary transmission No. dye Dye a* b* [%] .sup.1)F.sub.H1 .sup.2)F.sub.H2 .sup.3)F.sub.H3 .sup.4)F.sub.Z1 .sup.5)F.sub.Z2 .sup.5)F.sub.Z3 1 #9 #11 −1.2 −11.9 69 2.90 17.29 12.82 7.47 8.20 0.28 2 #9 #11 −1.8 −8.8 72 2.32 13.83 10.26 5.60 6.15 0.21 3 #9 #14 −1.6 −11.3 74 2.32 13.83 10.26 1.70 3.77 0.20 4 #7 #11 −3.0 −13.3 79 0.65 25.55 0.69 1.87 2.05 0.07 5 #7 #14 −1.5 −9.5 81 0.43 17.03 0.46 0.75 1.68 0.09 6 #12 #11 −2.7 −12.7 72 4.55 19.65 15.36 5.60 6.15 0.21 7 #12 #14 −1.2 −11.9 76 3.64 15.72 12.29 1.60 3.56 0.19 8 #11 #10 −1.8 −12.2 72 0.99 12.56 16.99 11.21 12.30 0.42 9 #10 #14 −1.1 −9.6 79 0.63 8.04 10.88 2.36 5.24 0.28 10 #1 #15 −2.0 −11.6 79 0.60 22.73 0.19 0.50 0.80 3.15 11 #19 #2 −1.1 −11.6 78 2.70 12.38 0.06 1.37 5.12 8.46 12 #3 #15 −1.2 −10.2 76 1.99 18.44 0.15 1.25 2.01 7.87 13 #19 #4 −1.1 −14.2 77 1.48 10.79 0.00 2.06 7.68 12.68 14 #5 #19 −1.5 −9.8 78 2.07 6.61 0.00 1.96 7.32 12.08 15 #6 #19 −1.7 −11.9 80 2.10 19.47 0.12 0.59 2.20 3.62 16 #8 #11 −2.3 −10.4 76 0.92 14.38 1.93 7.47 8.20 0.28 17 #8 #14 −1.3 −10.2 79 0.69 10.78 1.45 2.07 4.61 0.24 18 #19 #17 −0.09 −13.0 79 0.93 12.85 0.04 1.37 5.12 8.46 19 #11 #18 −0.09 −10.0 76 1.81 13.74 8.42 6.54 7.17 0.24 20 #18 #14 −1.0 −9.7 79 1.48 11.24 6.89 1.60 3.56 0.19 21 #7 #11 −2.0 −4.4 82 0.58 22.99 0.62 3.36 3.69 0.13 22 #1 #15 −1.8 −5.0 82 0.66 25.26 0.21 0.50 0.80 3.15 23 #5 #19 −2.2 −5.4 81 2.76 8.81 0.00 2.75 10.24 16.91 24 #10 #14 −2.5 −5.6 81 0.95 12.06 16.32 3.01 6.70 0.35 25 — — −0.61 5.83 87 — — — — — —

[00009]$\mathrm{where}$${}^{1)}F_{H1}=\frac{1}{1\mathrm{nm}}\underset{420\mathrm{nm}}{\overset{500\mathrm{nm}}{\int }}{E}_H\left(\lambda \right)d\lambda ;$${}^{2)}F_{H2}=\frac{1}{1\mathrm{nm}}\underset{520\mathrm{nm}}{\overset{600\mathrm{nm}}{\int }}{E}_H\left(\lambda \right)d\lambda ;$${}^{3)}F_{H3}=\frac{1}{1\mathrm{nm}}\underset{620\mathrm{nm}}{\overset{700\mathrm{nm}}{\int }}{E}_H\left(\lambda \right)d\lambda ;$${}^{4)}F_{Z1}=\frac{1}{1\mathrm{nm}}\underset{420\mathrm{nm}}{\overset{500\mathrm{nm}}{\int }}{E}_Z\left(\lambda \right)d\lambda ;$${}^{5)}F_{Z2}=\frac{1}{1\mathrm{nm}}\underset{520\mathrm{nm}}{\overset{600\mathrm{nm}}{\int }}{E}_Z\left(\lambda \right)d\lambda ;$${}^{6)}F_{Z3}=\frac{1}{1\mathrm{nm}}\underset{620\mathrm{nm}}{\overset{700\mathrm{nm}}{\int }}{E}_Z\left(\lambda \right)d\lambda$

and E.sub.H(λ) and E.sub.Z(λ) are the optical densities of the respective main dye and of the supplementary dye. The integrals of the optical densities over the wavelength ranges from 420 to 500 nm, from 520 to 600 nm and from 620 to 700 nm serve as a measure of the strength of absorption of the respective dye for blue, green-yellow and red light.

[0183] FIGS. 11 to 13 show graphs of the optical densities of the dyes used in the films of Examples 1 to 24 in absolute units as a function of the wavelength.