HK1070087B - Transparent molding composition for optical applications - Google Patents

Description

Transparent molding compositions suitable for optical applications

Technical Field

The invention relates to a molding composition based on transparent polyamide, which is suitable for optical applications. The material has a very faint intrinsic color while having UV blocking properties at about 400 nm. The object of the present invention is also moldings made from such molding compositions.

Background

Transparent polyamides are used, in addition to other plastics, such as Polycarbonate (PC) and polymethyl methacrylate (PMMA), as materials for producing spectacle frames, lenses, magnifying glasses, sunglasses, and for producing sighting devices, protective masks, optic disks and protective disks. Amorphous polyamides which are transparent per se are also suitable for this purpose; transparent, but microcrystalline polyamide materials are more suitable, since they have better chemical and stress crack resistance and higher scratch and abrasion resistance than those of completely amorphous transparent polyamides and PC or PMMA due to their crystalline fraction.

In optical applications, i.e. when transparent polyamides are used, for example, for the lenses of sunglasses, the aim is to prevent UV light from passing through the lenses, thereby avoiding damage to the glasses by light of this wavelength. The general idea, which is likewise applicable to transparent polyamide molding compositions, is to attempt to solve this task by introducing so-called UV absorbers or UV stabilizers.

DE19642885A1 and EP0837087A1 thus describe the addition of UV stabilizers to transparent polyamide molding compositions. It is clear, however, that in this case it is of crucial importance to strive for protection of the polymer.

WO02090421A1 describes a transparent thermoplastic polyamide molding composition which can be protected against UV light below 400nm by means of added UV absorbers or UV stabilizers.

DE3717928A1 also describes transparent polyamide molding compositions which may contain, in addition to other contents, brighteners. It is not derivable from this document whether UV blocking in the 370 to 430nm range can be achieved using a brightener.

By UV-blocking is herein understood that at certain specific wavelengths there is a transmission of less than 1% and that the slope of the transmission curve is positive at this point. After crossing this point, the transmission curve rises steeply.

The UV/VIS absorption spectrum of compounds used as UV absorbers or UV stabilizers shows a limited rise in the edge region. This means that no absorption decay occurs which jumps down from a very high value to zero. If the corresponding transmission curve is taken into account, it can be concluded that it has an S-shaped profile, with a limited rise in the curve in the transition region between zero and the maximum value of the predetermined layer thickness, which is determined by the particular substance. If, after the use of commercially available UV absorbers or UV stabilizers, it is possible to achieve light blocking at wavelengths below 400nm in transparent polyamide molding compositions, the molding compositions exhibit a pronounced yellow coloration owing to the absorption which inevitably occurs with the compounds used at wavelengths above 400 nm. This is disadvantageous for use. When used in sunglass lenses, production of weakly tinted lenses is limited. Weakly tinted lenses have many advantages in some applications and can increase the design freedom in designing sunglasses. When the weak coloration is carried out, the appearance of a noticeable yellow tinge in the molding composition is readily discernible, which can have an interfering effect. If a pigment suitable for masking such a color is additionally added, the original purpose of the weak coloring method is violated. In addition, some pigments at somewhat higher concentrations also cause a loss of transparency.

If, in order to avoid these disadvantages, a UV absorber is selected which, when present in the molding composition in the same concentration, has a significant transmission at lower wavelengths of light, for example 380nm, a molding composition with a weaker yellow shade is obtained, but at the same time sufficient UV protection is not ensured.

It is furthermore noted that the shape of the transmission curve of the molding composition can be influenced by the concentration of the absorber contained. Thus, a low addition of the same absorber generally results in a shift in the blocking capacity to a smaller wavelength range, while also generally improving the color. However, a full range of protection is not obtained.

In addition, yellowness can also result from thermal oxidative damage to the polymer.

The yellow colour value was evaluated by introducing the so-called b-value from the CIELAB colorimetric system (DIN 6174). In the positive range of b, a decrease in b means a decrease in yellow. If the value of b is negative, blue is exhibited.

Disclosure of Invention

It is therefore an object of the present invention to provide a molding composition which combines better the UV light-blocking properties with the smallest possible b-value for measuring the yellow color value of the molding composition and which therefore exceeds the hitherto known molding compositions in this respect by meeting both criteria at the same time.

Surprisingly, this object is achieved by a molding composition which is composed of at least 60% by weight of a transparent polyamide and which contains an effective amount of one or more brighteners which are present in an amount such that:

a) b value as a measure of the yellow color value is at most 7, preferably at most 6, more preferably at most 5, particularly preferably at most 4, most preferably at most 3, and

b) the transmission of 370 to 430nm, at least in the lower region, preferably at 400nm, is less than 1%, measured at a layer thickness of preferably 4mm, more preferably 2mm, particularly preferably 1 mm.

Transparent polyamides are already known (plastics handbook 3/4, hrsg. g.w.becker and g.braun, page 803, Carl Hanser press, munich, vienna, 1998). Suitable transparent polyamides within the scope of the present invention are also described, for example, in the following documents: U.S. Pat. No. 3, 2742496,CH-B-480381, CH-B-679861, DE-A-2225938, DE-A-2642244, DE-A-2743515, DE-A-2936759, DE-A-2732928, DE-A-3717928, DE-A-4310970, EP-A-0053876, EP-A-0271308, EP-A-0313436, EP-A-0725100, EP-A-5100721 and WO 02/090421.

The transparent polyamides used according to the invention can also be present in the form of copolyamides, which are prepared, for example, from the following monomers:

branched or unbranched aliphatic diamines having 6 to 14C atoms, such as 1, 6-hexamethylenediamine, 2-methyl-1, 5-diaminopentane, 2, 2, 4-or 2, 4, 4-trimethylhexamethylenediamine, 1, 9-nonanediamine, 1, 10-decanediamine or 1, 12-dodecamethylenediamine;

cycloaliphatic diamines having 6 to 22C atoms, such as 4, 4 '-diaminodicyclohexylmethane, 3, 3' -dimethyl-4, 4 '-diaminodicyclohexylmethane, 4, 4' -diaminodicyclohexylpropane, 1, 4-diaminocyclohexane, 1, 4-bis (aminomethyl) cyclohexane, 2, 6-bis (aminomethyl) norbornane or 3-aminomethyl-3, 5, 5-trimethylcyclohexylamine;

araliphatic diamines having 8 to 22C atoms, such as m-or p-xylylenediamine or bis (4-aminophenyl) propane;

branched or unbranched aliphatic dicarboxylic acids having 6 to 22C atoms, such as adipic acid, 2, 2, 4-or 2, 4, 4-trimethyladipic acid, azelaic acid, sebacic acid or 1, 12-dodecanedioic acid;

cycloaliphatic dicarboxylic acids having 6 to 22C atoms, such as cyclohexyl-1, 4-dicarboxylic acid, 4, 4 '-dicarboxydicyclohexylmethane, 3, 3' -dimethyl-4, 4 '-dicarboxydicyclohexylmethane, 4, 4' -dicarboxydicyclohexylpropane and 1, 4-bis (carboxymethyl) cyclohexane;

araliphatic dicarboxylic acids having 8 to 22C atoms, such as 4, 4' -diphenylmethanedicarboxylic acid;

aromatic dicarboxylic acids having 8 to 22C atoms, such as isophthalic acid, tributylisophthalic acid, terephthalic acid, 1, 4-, 1, 5-, 2, 6-or 2, 7-naphthalenedicarboxylic acid, diphenic acid or diphenyl ether-4, 4' -dicarboxylic acid;

lactams or corresponding omega-aminocarboxylic acids having 6 to 12C atoms, such as epsilon-caprolactam, epsilon-aminocaproic acid, octalactam, omega-aminocaprylic acid, omega-aminoundecanoic acid, dodecanelactam or omega-aminododecanoic acid.

Examples of transparent polyamides which can be used according to the invention are:

polyamides prepared from terephthalic acid and isomer mixtures of 2, 2, 4-and 2, 4, 4-trimethylhexamethylenediamine,

polyamides prepared from isophthalic acid and 1, 6-hexamethylenediamine,

copolyamides made from a terephthalic acid/isophthalic acid mixture and 1, 6-hexamethylenediamine,

copolyamides made from isophthalic acid, 3, 3 '-dimethyl-4, 4' -diaminodicyclohexylmethane and laurolactam or caprolactam,

(co) polyamides prepared from 1, 12-dodecanedioic acid or 1, 10-decanedioic acid, 3, 3 '-dimethyl-4, 4' -diaminodicyclohexylmethane and optionally also dodecanelactam or caprolactam,

copolyamides made from isophthalic acid, 4, 4' -diaminodicyclohexylmethane and laurolactam or caprolactone,

polyamides prepared from 1, 12-dodecanedioic acid and 4, 4' -diaminodicyclohexylmethane,

copolyamides made from a terephthalic/isophthalic acid mixture, 3, 3 '-dimethyl-4, 4' -diaminodicyclohexylmethane and laurolactam.

The transparent polyamide within the scope of the invention can also be a mixture of a plurality of different polyamides. One or more of the admixed components herein may also be in crystalline form. The only point is that such a mixture is transparent.

Brighteners work by a different mechanism than UV absorbers and UV stabilizers, because they re-release energy absorbed as radiation in the UV region, primarily as long-wave radiation in the visible range, rather than converting this energy into thermal energy. The process of releasing light by the brightener is done predominantly in the blue region of the visible spectrum, thereby counteracting yellow shades and producing a white effect, often with a blue hue. Due to this property, this class of compounds has long been preferred for use in fiber applications in the textile industry, but may also find application in other areas. Transparent systems are also included here. In this case, the brightener is mixed with UV absorbers and UV stabilizers, white pigments such as TiO₂Bluing agents, etc., in which case the brightener will improve the color of the system but will not block UV light. Such a method of application is described in EP1125968A 1. Brighteners can also be used in the transparent molding compositions and, in addition, in the polycarbonate molding compositions.

It is for example stated in WO01/92395A1 that brighteners can be used in addition to UV absorbers to improve the color properties. Such a corresponding use of brighteners is also found in EP0680996a 1. However, the use of brighteners which are purposefully employed in molding compositions to block the transmission of UV light while still achieving greatly improved yellow color values has not been disclosed to date.

Brighteners are commercially available under the product names, for example, Uvitex (Ciba Corp.) or Hostalux (Clariant Corp.), for example Hostalux KS, Hostalux KS1, Hostalux KSB (new variety) or Hostalux KS 1B. These brighteners, although based on a series of different chemical basic structures, all exhibit the above-mentioned fluorescence phenomena. Examples of the basic structure are stilbene (Uvitex OB-ONE from Ciba) or thiophene (Uvitex OB from Ciba), which are each substituted with a benzoxazole unit, and also dibenzothiazyl or biphenyl (Uvitex FP from Ciba), coumarin and the like. For further details, reference may be made to Ullmann encyclopedia of chemical industry, fifth edition, volume A18, VCH Press Weinheim, 1991, pages 153 to 176.

The amount of brightener used can be determined by simple experimentation. In the case of polyamides, the manufacturer recommends, for example, a maximum addition of 250ppm to the polymer, if a brightener of the brand Hostalux KS (Clariant) is used. At this addition level, UV blocking at 400nm was not yet visible. However, if the addition amount is increased by a factor of 10 to 100, a corresponding barrier phenomenon is observed in the transparent polyamide. These result in a very steep distribution of the transmission curve of the relevant molding composition in the transition region. If other brighteners are used, they can be adjusted to the desired optimum effect at other concentrations of the brightener in the molding composition, depending on their specific material properties. It is expected that the desired effect will occur in the range of 0.00001 to 10 wt%. It is clear that it is also possible here to use mixtures of different brighteners.

The b-value is determined in accordance with DIN53236 on 4mm thick cast (spritzgegossene) disks and in the incident light against a standard white background.

The transmission was measured according to astm d1003 on a casting pan.

In addition to the brighteners, it is also possible to include conventional UV absorbers or UV stabilizers in the molding compositions, but these embodiments are not preferred. Of course, the concentration of the UV absorber can be varied so that the desired UV protection effect does not occur due to its presence alone. These UV absorbers may have a range of chemical basic structures, typically for example benzotriazoles, triazines, benzophenones, anilides oxalates, cyanoacrylates, benzoxazinones and others.

The improvement, i.e.the reduction in the b value of the molding compositions used to measure the yellow color number of the polymers, while retaining the UV protection effect, can be achieved by using brighteners in combination with suitable stabilizers or stabilizer mixtures, such as antioxidants which can act as processing stabilizers. It is worth mentioning that: antioxidants containing phosphorus, sterically hindered phenolic compounds and compounds containing lower sulfur. It is particularly advantageous to add HALS stabilizers which likewise act as UV stabilizers, but which are another mechanism of action here. The mechanism is to chemically trap the free radicals formed on the polymer by the action of UV light, while the HALS stabilizer is consumed in the reaction. Such compounds are commercially available under the trade names Uvinol 4049H, Uvinol 4050H (BASF corporation), Cyasorb 3853, Cyasorb 3346(Cytec corporation), Tinuvin 770 or Tinuvin 622(Ciba corporation). The stabilization of the molding compositions by means of one or more antioxidants and/or HALS compounds not only improves the stability of the molding compositions during processing, but in particular also increases the duration of the action capability of the molding compositions within the scope of the present invention. Details of this matter can be found in Ullmann encyclopedia of chemical industry, fifth edition, volume A20, VCH Press Weinheim, 1992, pages 459 to 475.

In addition, the molding compositions may also contain the following additives:

other polymers, for example polymeric flow aids, as disclosed in EP1120443A2, polymeric flame retardants or impact modifiers, and also graft core-shell polymers of equal refractive index;

fillers or reinforcing materials, such as glass fibers or glass beads of equal refractive index and inorganic materials of nanometric order;

pigments, other dyes, plasticizers, antistatic agents, mold release agents, flow agents, flame retardants, etc.

The amount of all additives additionally added to the mixture of polyamide and brightener is preferably at most 30% by weight, more preferably at most 20% by weight and most preferably at most 10% by weight, based on the molding composition.

The molding compositions can be prepared, for example, by mixing the brightener and the additive into a twin-screw extruder or other process equipment which is capable of mixing solid substances into the polymer melt, or by adding the additive formulation to the equipment used to produce the polymer melt. Here, the brighteners and additives may be added as such or in the form of a masterbatch.

In addition, the respective components can also be added to the polycondensation reactor at the time of, before or after the polycondensation reaction or to a melting vessel or mixing vessel connected in front of the polycondensation reactor. It is likewise possible to mix the additives with the monomers, water or solvent and then to bring them to the polycondensation process. It is also possible to add the additives to the melt from the polycondensation process and simultaneously to the melt flowing out of the reaction apparatus, for example by means of a discharge extruder connected in series.

Another possible way of adding brighteners and stabilizers is to add them in the form of a solid phase, as described in DE 4301808A.

By designing polyamide molding compositions using the process according to the invention, it is possible for the first time to achieve a blocking of light waves having a wavelength of above 400nm, while the color b remains below 7. An additional safety margin against harmful wavelengths is thereby also created. The blocking position can be adjusted by changing the kind and amount of the added brightener according to the purpose of use. Generally, the barrier is in the use range of 370 to about 430 nm.

The corresponding molding compositions having the above-mentioned features a) and, if desired, b) can be used for producing the optical elements according to the invention. Optical elements here are those elements through which light can be transmitted, either in bundles or not, and which can then be observed by eye at the output end. Such as those used for spectacles, in particular for sunglasses, cameras, telescopes, magnifying glasses, microscopes, electro-optical measuring and testing devices, optical filters, projector lenses, lamp lenses, lenses for projectors and beamers, windows, sight glasses, protective glass sheets and sights, and sunroofs and glazings in the domestic or automotive sector. Furthermore, it is also possible to produce transparent moldings, fibers or films for various uses such as food packaging, pharmaceutical packaging, cosmetic packaging or agricultural films. The moulded part can be produced according to conventional plastic processing methods, for example by casting or extrusion.

The molding compositions of the invention can also be applied as clearcoats to optical elements of any composition. It is also possible to produce a film which contains a brightener and is, for example, post-injected, to give a lens or transparent molding.

In a further development of the invention, it is also possible to apply the brightener or a mixture of different brighteners as a further combined layer, for example a lacquer, to the optical element made of the transparent polyamide molding composition.

Within the scope of the invention, preferably in the range from 370 to 430nm, the transmission at least in the lower region is at most 10%, particularly preferably at most 6% or at most 5%, 4%, 3%, 2% or 1%, for a given layer thickness.

Examples 1 to 7 and comparative examples 1 to 5

1.Production of the Molding compositions:

using TROGAMID^®CX7323(Degussa Co.) as a starting material for the production of transparent polyamide molding compositions. The moisture content of the granules is less than 0.1% by weight.

The following were used as additives:

A：Hostalux^®KSp A benzoxazole derivative (brightener)

B：Hostalux^®KSBp, a mixture of benzoxazole derivatives (brighteners)

C：Hostalux^®KS1p, a benzoxazole derivative (brightener)

D：Hostalux^®KS1Bp, a benzoxazole derivative (brightener)

E：Irgafos^®168, a phosphite (thermal stabilizer)

F：Cyasorb^®1164A triazine derivative (UV absorber)

G：Cyasorb^®3638A benzoxazinone derivative (UV absorber)

H：Cyasorb^®3346, (poly [ 6-morpholino-s-triazine-2, 4-diyl) [2, 2, 6, 6-tetramethyl-4-piperidyl ] imino)]Hexamethylene [ (2, 2, 6, 6-tetramethyl-4-piperidyl) imino group]]UV absorbers)

J：Tinuvin^®326A benzotriazole derivative (UV absorber)

Additives were added via a powder mixture of additives and ground CX 7323; the processing is carried out in a double-screw extruder Berstorff ZE25-33D, the melting temperature is 280 ℃, and the rotating speed is 250s^-1. With a pressure of 40 bar. The resulting mixture was granulated and dried under vacuum at 100 ℃ until the water content obtained was at most 0.1% by weight. The time required here is generally 12 h.

The components of the resulting molding composition are shown in Table 1.

2. Production of sample pieces:

the resulting granules of the molding composition were produced into sample pieces by casting. The samples were made into rectangular disks 60X 2mm and circular disks 60X 4 mm. Production was done on a casting machine Engel ES 240/65 with a temperature of 280 ℃ and a mold temperature of 80 ℃.

3. Testing of the cast sample piece:

the transmission values were measured according to ASTM1003 on a measuring apparatus Lambda19 from Perkin Elmer. The regular transmittance was determined as described in section 4.3 of ASTM 1003. For this purpose, the two sample pieces were measured by placing the sample pieces 150mm from the inlet of the Ubbelohde sphere photometer.

The b value was measured in accordance with DIN53236 by means of a Minolta colorimetric CR-310. The geometry of the measurements was as follows: the observation was carried out by the gloss blocking method (Glanzeinschluss) at 0 ℃ or lower (d/o method). The measurement is made in a top view against the white reflector CR-a44(Minolta) with standard light D65; the spectral sensitivity of the test body corresponds to the standard found value of 2 °. The measurement procedure was carried out on circular discs of 60X 4 mm.

The test results are listed in table 2.

The transmission of the sample pieces of examples 1 to 4 and the transmission of the reference test (CX 7323 only) are compared in fig. 1. UV blocking at wavelengths greater than about 400nm can be observed with a dramatic increase in transmission.

It can be seen from FIG. 2 that if UV absorbers are used, either the blocking of UV light is insufficient (VB1-3) or the transmission, where it is comparable to the molding compositions of the invention, begins to decrease in the visible spectrum, leading to the development of a yellow sensation.

In FIG. 3, a molding composition containing a UV absorber (VB5) and a molding composition containing a further small amount of brightener (B7) are compared. It can be seen that this amount of UV absorber used does not meet the UV blocking requirements of the present invention.

Table 1:components of the Molding compositions (in parts by weight)

	CX7323	A	B	C	D	E	F	G	H	I
											R	100
B1	100	0.03
											B2	100		0.03
B3	100			0.03
											B4	100				0.03
B5	100			0.03		0.5
											B6	100				0.03	0.5
B7	100			0.03			0.1		0.1
											VB1	99						1
VB2	99.9						0.1
											VB3	99.9							0.1
VB4	99.8									0.2
											VB5	100						0.1		0.1

Reference test (R ═ R-

Example B

VB-control example

Table 2:measurement results

a) The measurements were made on a 2mm thick sample (all other measurements were made on a 4mm thick sample)

Example 8 and comparative example 6:manufacture of lenses

By casting the pellets of the molding compositions of example 5 and comparative example 4 thus obtained, a lens of 70mm diameter and 2.3mm thickness was obtained. The casting machine used here was Engel ES600 and had a melting temperature of 280 ℃ and a tool temperature of 80 ℃. An 8-fold lens mold was used.

The analytical measurement on the lens is similar to the measurement performed on the sample. The measurement results are shown in table 3, while the transmittance of the lens is compared in fig. 4.

Table 3:measurement results of lens

Claims (8)

1. Use of a molding composition consisting of at least 60% by weight of a transparent polyamide for the manufacture of an optical element, wherein the molding composition contains an effective amount of one or more brighteners in such an amount that:

a) b value as a measure of the yellow color value is at most 7, and

b) the transmission, measured with a layer thickness of 4mm, is less than 1% at 370 to 430nm, at least in the lower region.

2. An optical element made using a molding composition consisting of at least 60% by weight of a transparent polyamide, wherein the molding composition contains an effective amount of one or more brighteners in an amount such that the b-value, which is a measure of the yellow color value, is at most 7.

3. Optical element according to claim 2, characterized in that the transmission for a given thickness of the molding at least in the lower region is at most 10% at 370 to 430 nm.

4. Optical element according to claim 2 or 3 or manufactured according to claim 1, characterized in that the optical element is selected from the group consisting of optical lenses for spectacles, cameras, telescopes, loupes, microscopes or electro-optical measuring and testing devices, optical filters, searchlight lenses, lamp lenses, lenses for projectors and beamers, windows, sight glasses, protective glass slides and sights and sunroofs and glazings in the domestic or automotive field.

5. An optical element according to claim 2 or 3 or manufactured according to claim 1, which is a lens of sunglasses.

6. An optical element, characterized in that it has a multilayer structure and one layer consists of the molding composition according to claim 1.

7. An optical element made of transparent polyamide, characterized in that it is coated with a coating comprising one or more brighteners.

8. Optical element according to claim 7, characterized in that the coating is a layer of lacquer.