Disclosed are a capacitor for semiconductor devices capable of increasing storage capacitance and preventing leakage current, and method of manufacturing the same. The capacitor for semiconductor memory devices according to the present invention includes: a lower electrode; a dielectric layer formed on the lower electrode; and an upper electrode formed on the upper portion of the dielectric layer, wherein the dielectric layer is a crystalline TaxOyNz layer, and the total of x, y, and z in the crystalline TaxOyNz layer is 1, and y is 0.3 to 0.5, and z is 0.1 to 0.3.

The present invention relates to a capacitor for semiconductor memory device and a method of manufacturing the same, and more particularly to a capacitor for semiconductor memory device capable of increasing storage capacitance and preventing leakage current and method of manufacturing the same.
Along with the recent progress in the semiconductor manufacturing technology, the demand for memory device has increased dramatically. Consequently, a memory device having higher capacitance per small dimension is required. Capacitance of the capacitor is increased by using an insulator having high dielectric constant or enlarging the surface area of a lower electrode. Those conventional capacitors have been made with tantalum-oxide (Ta2O5) layer having a dielectric constant higher than that of nitride-oxide (NO) layer, thereby forming the lower electrode having 3-Dimensional structure.
FIG. 1 is a cross-sectional view of a capacitor in a conventional semiconductor memory device. Referring to FIG. 1, a field oxide layer 11 is also formed at a predetermined portion of the substrate 10. A gate electrode 13 including a gate insulating layer 12 at a lower portion thereof is formed by a known technique at a predetermined portion of a semiconductor substrate 10. A junction region 14 is formed on the semiconductor substrate 10 at each end of the gate electrode 13, thereby forming a MOS transistor. A first interlevel insulating layer 16 and a second interlevel insulating layer 18 are formed on the semiconductor substrate 10. A storage-node contact hole h is formed in the first and the second interlevel insulating layers 16, 18 so that the junction region 14 is exposed. A cylinder type lower electrode 20 is formed by a known technology with in the storage-node contact hole h to contact the exposed junction region 14. A HSG (hemi-spherical grain) layer 21 is formed on a surface of the lower electrode 20 in order to increase the surface area of the lower substrate 20. A Ta2O5 layer 23 is formed on the surface of the HSG layer 21. At this time, the Ta2O5 layer 23 is formed as follows. First, a surface of the HSG layer 21 is cleaned before the Ta2O5 layer 23 is formed, and then the RTN (rapid thermal nitridation) process is performed ex situ thereby forming a silicon-nitride layer 22 on the HSG layer 21. Next, a first Ta2O5 layer is formed at temperature of approximately 400-450xc2x0 C. with thickness of 53-57 xc3x85. Afterward, an annealing process is performed at low temperature, and then there is formed a second Ta2O5 layer with the same thickness and by the same process as in the first Ta2O5 layer. Annealing processes at low temperature and at high temperature are continued in series thereby forming a single Ta2O5 layer 23. An upper electrode 24 is deposited on upper portions of the Ta2O5 layer 23 and the second interlevel insulating layer 18, thereby completing the formation of a capacitor.
However, the conventional capacitor according to the above method using the Ta2O5 layer as a dielectric layer has the following problems.
First, a difference in the composition rate of Ta and O results since Ta2O5 generally has unstable stoichiometry. As a result, substitutional Ta atoms, i.e. vacancy atoms, are generated in the Ta2O5 layer. Since those vacancy atoms are oxygen vacancy, leakage current result. The amount of vacancy atoms in the dielectric layer can be controlled depending on the contents and the bond strength of components in the Ta2O5 layer; however, it is difficult to eliminate them completely.
In order to stabilize the unstable stoichiometry of Ta2O5, the Ta2O5 layer is oxidized so as to remove the substitutional Ta atoms in the Ta2O5 layer. However, when the layer is oxidized, an oxide layer having low dielectric constant is formed at an interface between the Ta2O5 layer and the lower electrode or the Ta2O5 layer and the upper electrode since Ta2O5 easily oxidizes with the lower and the upper electrode made of polysilicon or TiN., thereby degrading the homogeneity of the interface.
Further, due to the reaction between an organic substance such as Ta(OC2H5)5 used as a precursor and O2 (or N2O) gas as a reaction gas, impurities result, such as carbon atoms C, carbon compounds(CH4, C2H4) and H2O in the Ta2O5 layer. These impurities increase leakage current in the capacitor and degrade the dielectric characteristics of the Ta2O5 layer. Accordingly, a capacitor having a large capacitance is difficult to obtain.
Moreover, the use of the Ta2O5 layer as a dielectric layer generates extra ex-situ steps, one before formation of Ta2O5 layer and one after the cleaning step. Also, two thermal processes, at low and high temperatures, preferably is performed after the Ta2O5 layer has been formed. Therefore, forming a dielectric layer with Ta2O5 using the conventional method is cumbersome.
Accordingly, it is one object of the present invention to provide a capacitor for semiconductor device capable of obtaining a great capacitance by providing a dielectric layer having low leakage current and high dielectric constant.
Furthermore, the other object of the present invention is to provide a method of manufacturing capacitor for semiconductor device capable of simplifying its manufacturing process.
According to one aspect of the present invention, a capacitor for semiconductor memory device includes: a lower electrode; a dielectric layer formed on the lower electrode; and an upper electrode formed on the upper portion of the dielectric layer, wherein the dielectric layer is a crystalline TaxOyNz layer, and the total of x, y, and z in the crystalline TaxOyNz layer is 1, and y is 0.3 to 0.5, and z is 0.1 to 0.3.
In another aspect of the present invention, a method of manufacturing a capacitor on a semiconductor substrate includes the steps of: forming a lower electrode on the semiconductor substrate; depositing an amorphous TaxOyN2 layer as a dielectric layer on the lower electrode; crystallizing the amorphous TaxOyNz layer; and forming an upper electrode on the crystalline TaxOyNz layer, wherein the total of x, y and z in the TaxOyNz layer is 1, and y is 0.3 to 0.5, and z is 0.1 to 0.3.
Still other aspect of the present invention, a method of manufacturing a capacitor on a semiconductor substrate includes the steps of: forming a lower electrode on the semiconductor substrate; surface-treating to prevent a natural oxide layer generation on the surface of the lower electrode; depositing an amorphous TaxOyNz layer as a dielectric layer on the lower electrode; crystallizing the amorphous TaxOyNz layer; and forming an upper electrode on the crystalline TaxOyNz layer, wherein the total of x, y and z in the TaxOyNz layer is 1, y is 0.3 to 0.5, and z is 0.1 to 0.3, and the amorphous TaxOyNz layer is obtained by supplying Ta chemical vapor obtained from a precursor, O2 gas and NH3 gas with pressure of 0.1 to 100 Torr at temperature of 300 to 600xc2x0 C. in an LPCVD chamber and by a surface chemical reaction thereof.
Herein, O2 gas is supplied by 50 to 150 sccm and NH3 is supplied by 30 to 70 sccm.

Capacitor for semiconductor memory device and method of manufacturing the same

Hyundai Electronics Industries Co., Ltd.


A method of optical detection of characteristic quantities of an illuminated specimen comprising detecting a signal that is backscattered, reflected and/or fluoresced and/or transmitted from the specimen by a spatially resolving detector wherein radiation coming from the specimen is imaged on the detector, shifting the position of the radiation which is measured in a spatially resolved manner relative to the detector and determining intermediate values by an algorithm from the signals measured in different shifts for purposes of increasing the spatial resolution of the detector. An arrangement for performing the method is also disclosed.

a) Field of the Invention
The invention is directed to a method and an arrangement in fluorescence microscopy, particularly laser scanning microscopy, fluorescence correlation spectroscopy, and nearfield scanning microscopy, for examination of predominantly biological specimens, preparations and associated components. This includes methods for screening active ingredients based on fluorescence detection (high throughput screening). The transition from the detection of a few broad-spectrum dye bands to the simultaneous acquisition of whole spectra opens up new possibilities for the identification, separation and allocation of mostly analytic or functional specimen characteristics to spatial partial structures or dynamic processes. Therefore, simultaneous examination of specimens with multiple fluorophores with overlapping fluorescence spectra are even possible in three-dimensional or spatial structures of thick specimens. The spectral and spatial resolution of the detection unit is increased by means of the arrangement.
b) Description of the Related Art
A typical area of application of light microscopy for examining biological preparations is fluorescence microscopy (Pawley, "Handbook of Biological Confocal Microscopy"; Plenum Press 1995). In this case, determined dyes are used for specific labeling of cell parts.
The irradiated photons having a determined energy excite the dye molecules, through the absorption of a photon, from the ground state to an excited state. This excitation is usually referred to as one-photon or single-photon absorption (FIG. 1a). The dye molecules excited in this way can return to the ground state in various ways. In fluorescence microscopy, the most important is the transition with emission of a fluorescence photon. Because of the Stokes shift, there is generally a red shift in the wavelength of the emitted photon in comparison to the excitation radiation; that is, it has a greater wavelength. Stokes shift makes it possible to separate the fluorescence radiation from the excitation radiation.
The fluorescent light is split off from the excitation radiation by suitable dichroic beam splitters in combination with blocking filters and is observed separately. This makes it possible to show individual cell parts that are dyed with different dyes. In principle, however, several parts of a preparation can also be dyed simultaneously with different dyes which bind in a specific manner (multiple fluorescence). Special dichroic beam splitters are used again to distinguish the fluorescence signals emitted by the individual dyes.
In addition to excitation of dye molecules with a high-energy photon (single-photon absorption), excitation with a plurality of low-energy photons is also possible (FIG. 1b). The sum of energies of the single photons corresponds approximately to a multiple of the high-energy photon. This type of excitation of dyes is known as multiphoton absorption (Corle, Kino, "Confocal Scanning, Optical Microscopy and Related Imaging Systems"; Academic Press 1996). However, the dye emission is not influenced by this type of excitation, i.e., the emission spectrum undergoes a negative Stokes shift in multiphoton absorption; that is, it has a smaller wavelength compared to the excitation radiation. The separation of the excitation radiation from the emission radiation is carried out in the same way as in single-photon excitation.
The prior art will be explained more fully in the following by way of example with reference to a confocal laser scanning microscope (LSM) (FIG. 2).
An LSM is essentially composed of four modules: light source, scan module, detection unit and microscope. These modules are described more fully in the following. In addition, reference is had to DE19702753A1.
Lasers with different wavelengths are used in an LSM for specific excitation of different dyes in a preparation. The choice of excitation wavelengths is governed by the absorption characteristics of the dyes to be examined. The excitation radiation is generated in the light source module. Various lasers (argon, argon/krypton, Ti:Sa lasers) are used for this purpose. Further, the selection of wavelengths and the adjustment of the intensity of the required excitation wavelength is carried out in the light source module, e.g., using an acousto-optic crystal. The laser radiation subsequently reaches the scan module via a fiber or a suitable mirror arrangement.
The laser (Laser A-D) radiation generated in the light source is focused in the preparation in a diffraction-limited manner by means of the objective (2) via the scanner, scanning optics and tube lens. The focus scans the specimen in a point raster in x-y direction. The pixel dwell times when scanning over the specimen are mostly in the range of less than one microsecond to several seconds.
In confocal detection (descanned detection) of fluorescent light, the light emitted from the focal plane (specimen) and from the planes located above and below the latter reaches a dichroic beam splitter (MDB) via the scanner. This dichroic beam splitter separates the fluorescent light from the excitation light. The fluorescent light is subsequently focused on a diaphragm (confocal diaphragm/pinhole) located precisely in a plane conjugate to the focal plane. In this way, fluorescent light components outside of the focus are suppressed. The optical resolution of the microscope can be adjusted by varying the size of the diaphragm. Another dichroic blocking filter (EF(1-5) which again suppresses the excitation radiation is located behind the diaphragm. After passing the blocking filter, the fluorescent light is measured by means of a point detector (PMT1-5).
When using multiphoton absorption, the excitation of the dye fluorescence is carried out in a small volume at which the excitation intensity is particularly high. This area is only negligibly larger than the detected area when using a confocal arrangement. Accordingly, a confocal diaphragm can be dispensed with and detection can be carried out directly following the objective (non-descanned detection).
In another arrangement for detecting a dye fluorescence excited by multiphoton absorption, descanned detection is carried out again, but this time the pupil of the objective is imaged in the detection unit (nonconfocal descanned detection).
From a three-dimensionally illuminated image, only the plane (optical section or slice) located in the focal plane of the objective is reproduced by the two detection arrangements in connection with corresponding single-photon absorption or multiphoton absorption. By recording or plotting a plurality of optical slices in the x-y plane at different depths z of the specimen, a three-dimensional image of the specimen can be generated subsequently in computer-assisted manner.
Accordingly, the LSM is suitable for examination of thick preparations. The excitation wavelengths are determined by the utilized dye with its specific absorption characteristics. Dichroic filters adapted to the emission characteristics of the dye ensure that only the fluorescent light emitted by the respective dye will be measured by the point detector.
Currently, in biomedical applications, a number of different cell regions are labeled simultaneously by different dyes (multifluorescence). In the prior art, the individual dyes can be detected separately based on different absorption characteristics or emission characteristics (spectra) (FIG. 3a). For example, emission signals are plotted over wavelength for different dyes (1-4). For separate detection, an additional splitting of the fluorescent light of a plurality of dyes is carried out with the secondary beam splitters (DBS) and a separate detection of the individual dye emissions is carried out in separate point detectors (PMT x). With the arrangement described above, it is impossible for the user to flexibly adapt detection and excitation to corresponding new dye characteristics. Instead, new dichroic beam splitters and blocking filters must be created for every (new) dye. In an arrangement according to WO9507447, the fluorescent light is split spectrally by means of a prism. The method differs from the above-described arrangement with dichroic filters only in that the characteristic of the utilized filter is adjustable. However, it is still preferable to record the emission band of a dye by point detector.
Fast local measurement of the emission spectrum is possible only conditionally with the two arrangements, since the adjustment of the emission range relies on mechanical movements of the dichroic filter and diaphragms and the maximum spectral resolution is therefore limited to some 5 nm. A high spectral resolution is needed, for example, when the emission spectra overlap as is shown in FIG. 3b. FIG. 3b shows behavior of this kind in the two naturally occurring dyes CFP and GFP. These dyes are particularly suited to examination of living preparations because they have no toxic effect on the specimens to be examined.
When the position of the emission spectrum of the utilized dyes is unknown or when a shift occurs in the emission spectrum depending on environment (FIG. 3c), high-resolution detection of the dye fluorescence is necessary. The wavelength shift can amount to several times 10 nm. Spectrometers are also currently used in combination with an LSM to measure the emission spectrum in the specimen. In so doing, a conventional, usually high-resolution spectrometer is used instead of a point detector (Patent: Dixon, et al. U.S. Pat. No. 5,192,980). However, these spectrometers can record an emission spectrum only point by point or as an average over a region. Thus, this is a type of spectroscopy. In addition, the usually weak fluorescence signal of the specimen is distributed to a large quantity of individual channels in the spectrometer (usually 512 or 1024 individual channels) or a narrow fluorescence band is detected corresponding to the spectral resolution. Therefore, the signal per individual channel is extremely small and in some cases is not detectable.
Line scanners, as they are called, are also used according to the prior art in place of point scanners (Corle, Kino, "Confocal Scanning Optical Microscopy and Related Imaging Systems"; Academic Press 1996). The basic construction essentially corresponds to that of an LSM according to FIG. 2. However, instead of a point focus, a line is imaged in the focus and the specimen to be examined is scanned in only one direction. A slit diaphragm is used as confocal diaphragm instead of a pinhole diaphragm in a construction of this kind. Non-descanned detection can also be carried out with this arrangement using multiphoton absorption. The confocal diaphragm can again be omitted in this case. Usually, a CCD line with 1024 or more image points is used for detection. The image acquisition rate is increased considerably by scanning a line instead of a point. This scanning method can accordingly be used for observation of fast-running processes in real time.
It is disadvantageous in the methods according to the prior art that the line detector must usually be read out sequentially, so that increased readout noise can result at fast readout rates.

Method for increasing the spectral and spatial resolution of detectors


A system includes an oxidant compressor and a gas turbine engine. The gas turbine engine includes a combustor section having a turbine combustor, a turbine driven by combustion products from the turbine combustor, and an exhaust gas compressor driven by the turbine. The exhaust gas compressor is configured to compress and route an exhaust flow to the turbine combustor and the oxidant compressor is configured to compress and route an oxidant flow to the turbine combustor. The gas turbine engine also includes an inlet oxidant heating system configured to route at least one of a first portion of the combustion products, or a second portion of the exhaust flow, or any combination thereof, to an inlet of the oxidant compressor.

The subject matter disclosed herein relates to gas turbine engines, and more specifically, to systems and methods for an oxidant heating system for gas turbine engines.
Gas turbine engines are used in a wide variety of applications, such as power generation, aircraft, and various machinery. Gas turbine engines generally combust a fuel with an oxidant (e.g., air) in a combustor section to generate hot combustion products, which then drive one or more turbine stages of a turbine section. In turn, the turbine section drives one or more compressor stages of a compressor section. Again, the fuel and oxidant mix in the combustor section, and then combust to produce the hot combustion products. Under certain conditions, such as low temperatures, the compressor section may be susceptible to undesirable issues, such as icing and/or surging. Therefore, it may be desirable to increase an inlet temperature of the compressor section to reduce issues associated with low temperatures. Furthermore, gas turbine engines typically consume a vast amount of air as the oxidant, and output a considerable amount of exhaust gas into the atmosphere. In other words, the exhaust gas is typically wasted as a byproduct of the gas turbine operation.

System and method for an oxidant heating system


A method and structure for a complementary metal oxide semiconductor active pixel sensor device having a photodetector, a sensing node electrically connected to the photodetector, an output connected to the photodetector, and a voltage-independent capacitance device connected between the sensing node and the output. The voltage-independent capacitance device provides a capacitance independently of a voltage on the sensing node. The voltage-independent capacitance device can be a voltage-independent capacitor, an electrode-electrode capacitor, or a common source amplifier and should have a capacitance larger than the capacitance of the sensing node. The voltage-independent capacitance device lowers an overall voltage-dependent capacitance of the APS.

The present invention generally relates to complementary metal oxide semiconductor (CMOS) active pixel sensors (APS) and more particularly to an improved pixel sensor that has increased linearity as a result of additional voltage-independent capacitance.
CMOS APS are solid state imagers where each pixel contains a photo-sensing means, reset means, charge conversion means, select means, and all or part of an amplifier. APS devices have the advantages of single supply operation, lower power consumption, x-y addressability, image windowing, and the ability to effectively integrate signal processing electronics on-chip, when compared to CCD sensors.
In order to build high resolution, small pixel APS devices for digital cameras it is necessary to use sub-xcexcm CMOS processes in order to minimize the area of the pixel allocated the active components in each pixel. In order to achieve good signal to noise performance it is important to hold as many photoelectrons as possible within the pixel. In typical APS pixel architectures the integrated photoelectrons are converted to a voltage in each pixel. This charge to voltage conversion region is typically a diode, either the photodiode or an isolated floating diffusion. It is the parasitic capacitance of the charge to voltage conversion region that determines the maximum number of electrons that can be contained within the region. Sub-xcexcm CMOS processes are typically operated at low supply voltages, 3.3V and below, hence the reset level and the voltage swing that can be accommodated in the charge to voltage conversion region is limited by the supply voltage. Since the supply voltage is low, the signal swing on the charge to voltage conversion region is a large compared to the reset level. Since the capacitance of the diode that forms the charge to voltage conversion region is a function of the voltage across the diode, and the signal swing is large compared to the total voltage across the diode at reset, the capacitance of the diode changes substantially from the reset level, (or dark signal), to the saturation level, (or bright signal). In typical APS pixel architectures the capacitance at reset is smaller than the capacitance at saturation. This produces a non-linear transfer function. It is very important to have a linear transfer function for color image sensors. Non-linearity in the sensor response can degrade the color fidelity of the image. Response linearity has been optimized for CCD image sensors. APS are much less linear that CCD""s.
In addition to poor linearity, APS sensors can also suffer from low charge capacity as a result of the reduced supply voltages in sub-xcexcm CMOS processes. For the same pixel size, CMOS APS sensors have lower charge capacity compared to CCD image sensors due to the larger supply and clock voltages used on CCD image sensors.
One approach to providing an image sensor with the linearity of a CCD and the advantages of an APS device is to reduce the effect of the voltage dependent capacitance of the charge to voltage conversion region of an APS device. This invention does so by providing a voltage independent capacitor in parallel with the diode capacitance of the charge to voltage conversion region. This can also be used to improve the charge capacity of an APS device.
It is, therefore, an object of the present invention to provide a structure and method for a complementary metal oxide semiconductor active pixel sensor device having a photodetector, a charge to voltage conversion node, an amplifier input connected to the charge to voltage conversion node, and a voltage-independent capacitance connected in parallel with the charge to voltage conversion node. The voltage-independent capacitance provides a capacitance that is not a function of charge placed on the charge to voltage conversion node. The voltage-independent capacitance can be an electrode-electrode capacitor, or the input capacitance of an amplifier.
The invention also comprises a method of manufacturing a complementary metal oxide semiconductor active pixel sensor device which includes a photodetector, a charge to voltage conversion node, an amplifier input connected to the charge to voltage conversion node, and a voltage-independent capacitance connected in parallel with the charge to voltage conversion node. The voltage-independent capacitance provides a capacitance that is not a function of charge placed on the charge to voltage conversion node. The voltage-independent capacitance can be an electrode-electrode capacitor, or the input capacitance of an amplifier.

Linearity and dynamic range for complementary metal oxide semiconductor active pixel image sensors


A semiconductor component and a method of manufacturing the semiconductor component that reduces parasitic elements. A semiconductor chip is coupled to a semiconductor chip receiving area of a support structure. The semiconductor chip has at least two power semiconductor devices. A drain contact of a first power semiconductor device is coupled to a source contact of a second power semiconductor device and the drain and source contacts of the first and second power semiconductor devices are joined to the semiconductor chip receiving area. Another semiconductor chip may be bonded to a second semiconductor chip receiving area of the support structure. An energy storage element may be coupled between the source contact of the first power semiconductor device and the drain contact of the second semiconductor device. A protective structure may be formed over the semiconductor chips and the energy storage element.

Semiconductor components may be used in applications such as voltage regulators. In a voltage regulator, two separate packaged field effect transistors are coupled together to form a switching network having a switching node that is typically coupled to an output terminal through an inductor. It is desirable for the switching network to have a small form factor for both portable and non-portable applications. The form factor may be decreased by decreasing the size of the field effect transistors and increasing the switching frequency of the switching network. This allows reducing the size of the passive components such as, for example, the inductor coupled to the output terminal. In addition to reducing the sizes of the passive components, it is desirable to reduce the sizes of the elements that contribute to the formation of interconnect parasitic passive elements such as resistances, inductances, and capacitances. Forming the switching network from discrete transistors increases the parasitic inductance distribution which increases the switching energy dissipation of the voltage regulator.
Accordingly, it would be advantageous to have a semiconductor component and a method for manufacturing the semiconductor component that allows for a smaller form factor and a reduction in the parasitic elements. It would be of further advantage for the semiconductor component to be cost efficient to manufacture.

Method for manufacturing a semiconductor component and structure therefor

Semiconductor Components Industries, LLC


The invention relates to a co-extruded, biaxially oriented polyester film consisting of a base layer and at least one outer layer. The film contains at least one flame-retardant agent, at least one UV-stabilizer and has a matt outer layer which contains a mixture and/or a blend of two components (I) and (II), whereby component (I) is substantially a polyethylene terephthalate homopolymer, or a polyethylene terephthalate copolymer, or a mixture of polyethylene terephthalate homopolymers or polyethylene terephthalate copolymers, and component (II) is a polymer containing at least one sulphonate group.

The invention relates to a biaxially oriented polyester film with a base layer composed of at least 70% by weight of a thermoplastic polyester and comprising at least one UV stabilizer and one flame retardant, and with at least one matt outer layer which comprises a mixture or, respectively, a blend made from two components I and II. The invention further relates to the use of the film and to a process for its production.
Component I of the mixture or blend is a polyethylene terephthalate homopolymer or polyethylene terephthalate copolymer, or a mixture of polyethylene terephthalate homo- or copolymers.
Component II of the mixture or blend is a polyethylene terephthalate copolymer which is composed of the condensation product of the following monomers or, respectively, of their derivatives capable of forming polyesters: isophthalic acid, aliphatic dicarboxylic acid, sulfomonomer which contains a metal sulfonate group on the aromatic moiety of an aromatic dicarboxylic acid, and aliphatic or cycloaliphatic glycol.
The outer layer of the invention has a characteristic matt surface or appearance and is very suitable for use in constructing exhibition stands, in greenhouses, or for industrial applications, in particular where a requirement is UV resistance or impermeability to UV light and flame retardancy to DIN 4102 Part 2, construction materials class B2 and B1.
There is high industrial demand for transparent, high-gloss plastic films, e.g. biaxially oriented propylene films or biaxially oriented polyester films. There is also an increasing demand for transparent films of this type which are flame retardant to DIN 4102 and which have at least one surface layer which is not high-gloss but has a characteristic matt appearance and therefore, for example, provides the application with an appearance which is particularly attractive and therefore effective for promotional purposes, and provides protection from UV radiation while also providing flame retardancy.
U.S. Pat. No. 4,399,179 describes a coextruded biaxially oriented polyester film which is composed of a transparent base layer and of at least one matt layer which essentially consists of a certain polyethylene terephthalate copolymer and also comprises inert particles with a diameter of from 0.3 to 20 xcexcm at a concentration of from 3 to 40%. The specific copolymer is a processing aid which reduces the viscosity of the melt comprising the inert particles, thus permitting satisfactory extrusion of that layer. The mattness of the film is achieved by adding the inert particles to the appropriate layer.
EP 0 144 978 describes a self-supporting oriented film made from thermoplastic and, on at least one of its two surfaces, bearing a continuous polyester coating which is applied as aqueous dispersion to the film prior to the final stretching step. The polyester coating is composed of a condensation product of various monomers which are capable of forming polyesters, such as isophthalic acid, aliphatic dicarboxylic acid, sulfomonomers, and aliphatic or cycloaliphatic glycols.
EP-A-0 620 245 describes films with improved heat resistance. These films comprise antioxidants which are suitable for scavenging free radicals formed in the film and degrading any peroxide formed. However, that specification gives no proposal as to how the UV resistance of films of that type might be improved.
DE-A 2346 787 describes a flame-retardant, phospholane-modified polymer. Besides the polymer, the use of the polymer to give films and fibers is also claimed. When films were produced from this phospholane-modified polymer the following shortcomings were apparent:
The polymer is very susceptible to hydrolysis and has to be very effectively predried. When the polymer is dried with prior art dryers it cakes, and production of a film is therefore possible only under very difficult conditions.
The films produced, under extreme and uneconomic conditions, also embrittle at high temperatures. The associated decline in mechanical properties is so severe as to make the film unusable. This embrittlement occurs after as little as 48 hours of exposure to heat.
The instances described give no indication as to how at least one surface of the film can be provided with low gloss while retaining high film transparency, or how the film is to absorb UV light, or how the film is to be provided with high UV resistance and also flame retardancy.
It was therefore an object of the present invention to provide a coextruded biaxially oriented and transparent polyester film which has at least one matt outer layer and whose production is simple and cost-effective, and which has the good physical properties of known films, causes no disposal problems, and in particular absorbs UV light and has high UV resistance, and also is flame-retardant to DIN 4102, and does not embrittle on exposure to heat.
This object is achieved by means of a coextruded and biaxially oriented polyester film of the generic type mentioned at the outset, the characterizing features of which are that the film comprises at least one UV stabilizer and at least one flame retardant, the flame retardant and, where appropriate, the UV stabilizer being fed by way of masterbatch technology, and has a matt outer layer which comprises a mixture or, respectively, a blend made from two components I and II.
Component I of the mixture or blend is a polyethylene terephthalate homopolymer or polyethylene terephthalate copolymer, or a mixture made from polyethylene terephthalate homo- or copolymers.
Component II of the copolymer or of the mixture or blend is a polymer containing at least one sulfonate group, in particular a condensation product of the following monomers or of their derivatives capable of forming polyesters:
A) from 65 to 95 mol % of isophthalic acid;
B) from 0 to 30 mol % of at least one aliphatic dicarboxylic acid with the formula
HOOC(CH2)nCOOH
where
n is from 1 to 11;
C) from 5 to 15 mol % of at least one sulfomonomer containing an alkali metal sulfonate group on the aromatic moiety of a dicarboxylic acid;
D) a copolymerizable aliphatic or cycloaliphatic glycol having from 2 to 11 carbon atoms, in the stoichiometric amount necessary to form 100 mol % of condensate;
where each of the percentages given is based on the total amount of the monomers forming component II.
High UV resistance means that sunlight or other UV radiation causes no, or only extremely little, damage to the films, and that the films are therefore suitable for outdoor applications and/or critical indoor applications. In particular, the films should not yellow after a number of years of outdoor use, nor display any embrittlement or cracking of the surface, nor should their mechanical properties deteriorate. High UV resistance therefore means that the film absorbs UV light and does not transmit light until the visible region has been reached.
The good mechanical properties include high modulus of elasticity (EMD greater than 3200 N/mm2; ETD greater than 3500 N/mm2) and also good values for tensile strength at break (in MD greater than 100 N/mm2; in TD greater than 130 N/mm2).
Good orientability includes the capability of the film to give excellent orientation both longitudinally and transversely during its production, without break-offs.
Cost-effective production includes the capability of the raw materials or raw material components needed for producing the flame-retardant film to be dried using conventional industrial dryers. It is important that the raw materials do not cake or undergo thermal degradation. These prior art industrial dryers include vacuum dryers, fluidized-bed dryers, and fixed-bed dryers (tower dryers). These dryers operate at temperatures from 100 to 170xc2x0 C., at which polymers provided with flame retardancy by conventional methods cake and eventually have to be removed by force, making film production impossible. In the case of the vacuum dryer, which has the gentlest drying action, the raw material usually passes through a range of temperatures from about 30 to 130xc2x0 C. at a subatmospheric pressure of 50 mbar. This has to be followed by what is known as post-drying in a hopper at temperatures from 100 to 130xc2x0 C. with a residence time of from 3 to 6 hours. Even here, the known polymers cake to an extreme extent.
No embrittlement on short exposure to heat means that after 100 hours of controlled heating at 100xc2x0 C. in a circulating-air drying cabinet the film has not embrittled and does not have poor mechanical properties.
For the purposes of the present invention, mixtures are mechanical mixtures prepared from the individual components. For this, the individual constituents are generally combined in the form of small-dimensioned compressed moldings, e.g. lenticular or bead-shaped pellets, and mixed with one another mechanically, using a suitable agitator. Another way of producing the mixture is to feed components I and II in pellet form separately to the extruder for the outer layer of the invention, and to carry out the mixing in the extruder and/or in the downstream systems for transporting the melt.
For the purposes of the present invention, a blend is an alloy-like composite of the individual components I and II which can no longer be separated into the initial constituents. A blend has properties like those of a homogeneous material and can therefore be characterized by appropriate parameters.
According to the invention, the film has at least two layers. The layers which it then encompasses are a layer B (=base layer) and the outer layer A of the invention. In one preferred embodiment of the invention, the film has a three-layer structure, and has the outer layer A on one side of the layer B (=base layer) and has another layer C on the other side of the layer B. In this case, the two layers A and C form the outer layers A and C. According to the invention, the UV stabilizer and the flame retardant may be present in the outer layer(s) and/or in the base layer.
The base layer B of the film is preferably composed of at least 70% by weight of a thermoplastic polyester. Polyesters suitable for this purpose are those made from ethylene glycol and terephthalic acid (=polyethylene terephthalate, PET), from ethylene glycol and naphthalene-2,6-dicarboxylic acid (=polyethylene 2,6-naphthalate, PEN), from 1,4-bishydroxymethylcyclohexane and terephthalic acid (=poly-1,4-cyclohexanedimethylene terephthalate, PCDT), or else made from ethylene glycol, naphthalene-2,6-dicarboxylic acid and biphenyl-4,4xe2x80x2-dicarboxylic acid (=polyethylene 2,6-naphthalate dibenzoate, PENBB). Particular preference is given to polyesters at least 90 mol %, preferably at least 95 mol %, of which is composed of ethylene glycol units and terephthalic acid units, or of ethylene glycol units and naphthalene-2,6-dicarboxylic acid units. The remaining monomer units derive from those other aliphatic, cycloaliphatic or aromatic diols and dicarboxylic acids. Other examples of suitable aliphatic diols are diethylene glycol, triethylene glycol, aliphatic glycols of the formula HOxe2x80x94(CH2)nxe2x80x94OH, where n is an integer from 3 to 6 (in particular 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol) and branched aliphatic glycols having up to 6 carbon atoms. Among the cycloaliphatic diols, mention should be made of cyclohexanediols (in particular 1,4-cyclohexanediol). Examples of other suitable aromatic diols have the formula HOxe2x80x94C6H4xe2x80x94Xxe2x80x94C6H4xe2x80x94OH, where X is xe2x80x94CH2xe2x80x94, xe2x80x94C(CH3)2xe2x80x94, xe2x80x94C(CF3)2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94SO2xe2x80x94. Bisphenols of the formula HOxe2x80x94C6H4xe2x80x94C6H4xe2x80x94OH are also very suitable.
Other aromatic dicarboxylic acids are preferably benzenedicarboxylic acids, naphthalene dicarboxylic acids (such as naphthalene-1,4- or -1,6-dicarboxylic acid), biphenyl-x,xxe2x80x2-dicarboxylic acids (in particular biphenyl-4,4xe2x80x2-dicarboxylic acid), diphenylacetylene-x,xxe2x80x2-dicarboxylic acids (in particular diphenylacetylene-4,4xe2x80x2-dicarboxylic acid) or stilbene-x,xxe2x80x2-dicarboxylic acids. Among the cycloaliphatic dicarboxylic acids mention should be made of cyclohexanedicarboxylic acids (in particular cyclohexane-1,4-dicarboxylic acid). Among the aliphatic dicarboxylic acids, the C3-C19 g alkanediacids are particularly suitable, and the alkane moiety here may be straight-chain or branched.
One way of preparing the polyesters is the transesterification process. Here, the starting materials are dicarboxylic esters and diols, which are reacted using the customary transesterification catalysts, such as the salts of zinc, of calcium, of lithium, of magnesium or of manganese. The intermediates are then polycondensed in the presence of well-known polycondensation catalysts, such as antimony trioxide or titanium salts. Another equally good preparation method is the direct esterification process in the presence of polycondensation catalysts. This starts directly from the dicarboxylic acids and the diols.
At least one outer layer of the multilayer film of the invention comprises a mixture or, respectively, a blend made from two components I and II and described in more detail below, and, where appropriate, comprises additives.
Component I of the outer layer mixture or of the blend essentially consists of a thermoplastic polyester, in particular the polyester described in more detail for the base layer. A method which has proven successful here for achieving a high degree of mattness is to use a polyester of comparatively low viscosity for component I of the outer layer of the invention. To describe the viscosities of the melts use is made of a modified solution viscosity (SV or xe2x80x9cstandard viscosityxe2x80x9d). The SVs of commercially available polyethylene terephthalates suitable for producing biaxially oriented films are in the range from 500 to 1200. A method which has proven successful for obtaining a high degree of film mattness for the purposes of the present invention is to use polymers whose SV is in the range from 500 to 800, preferably in the range from 500 to 750, particularly preferably in the range from 500 to 700, for component I of the outer layer of the invention.
As stated above, component II of the outer layer mixture is obtained by condensation of the following monomers or of their derivatives capable of forming polymers:
A) isophthalic acid,
B) if appropriate, an aliphatic dicarboxylic acid of the formula
HOOC(CH2)nCOOH
where
n is in the range from 1 to 11,
C) a sulfomonomer containing an alkali metal sulfonate group on the aromatic moiety of an aromatic dicarboxylic acid, and
D) an aliphatic or cycloaliphatic glycol having from 2 to 11 carbon atoms, in the amount needed to form 100 mol % of condensate.
The total molar equivalents of acid present should be substantially the same as the total equivalents of glycol present.
Examples of dicarboxylic acids suitable as component B) of the copolyesters are malonic, adipic, azelaic, glutaric, sebacic, suberic, succinic and brassylic acid, and also mixtures of these acids or their derivatives capable of forming polyesters. Of the abovementioned acids, sebacic acid is preferred.
Examples of sulfomonomers which contain a metal sulfonate group on the aromatic moiety of an aromatic dicarboxylic acid (component C) are monomers of the following formula:
where
M is a monovalent cation of an alkali metal,
Z is a trivalent aromatic radical, and
X and Y are carboxy groups or polyester-forming equivalents.
Monomers of this type are described in U.S. Pat. Nos. 3,563,942 and 3,779,993. Examples of monomers of this type are the sodium salts of sulfoterephthalic acid, of 5-sulfoisophthalic acid, of sulfophthalic acid, of 5-(p-sulfophenoxy)isophthalic acid, or of 5-sulfopropoxyisophthalic acid, and similar monomers, and also derivatives of these, such as the dimethyl esters, capable of forming polyesters. M is preferably Na+, Li+, or K+.
The term xe2x80x9cderivatives capable of forming polyestersxe2x80x9d here means reaction participants with groups capable of condensation reactions, in particular transesterification reactions, to form polyester bonds. Groups of this type include carboxy groups. They also include the lower alkyl esters of these, e.g. dimethyl terephthalate, diethyl terephthalate, and numerous other esters, halides, and salts. The acid monomers are preferably used in the form of dimethyl esters, since this permits better control of the condensation reaction.
Examples of glycols suitable as component D) are ethylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 1,10-decanediol, cyclohexanedimethanol, and similar substances. It is preferable to use ethylene glycol.
The copolyesters may be prepared by known polymerization techniques. The procedure is generally to combine the acid components with glycol and to heat these in the presence of an esterification catalyst, with subsequent addition of a polycondensation catalyst.
The quantitative ratios of components A, B, C, and D used to prepare the mixtures of the invention have been found to be decisive for obtaining the matt outer layer. For example, at least about 65 mol % of isophthalic acid (component A) has to be present as acid component. Component A is preferably from about 70 to 95 mol % of pure isophthalic acid.
As far as component B is concerned, any acid with the formula mentioned gives satisfactory results, and preference is given to adipic acid, azelaic acid, sebacic acid, malonic acid, succinic acid, glutaric acid, and mixtures of these acids. The desired amount within the range given is preferably from 1 to 20 mol %, based on the acid components of the mixture II, if component B is present in the composition.
The amount of the glycol component present is stoichiometric.
The copolyesters suitable for the purposes of the invention also have an acid value below 10, preferably from 0 to 3, an average molecular weight below about 50,000, and an SV in the range from about 30 to 700, preferably from about 350 to 650.
The ratio (ratio by weight) of the two components I and II of the outer layer mixture or blend may vary within wide limits and depends on the intended use of the multilayer film. The ratio of components I and II is preferably in the range from I:II=10:90 to I:II=95:5, preferably from I:II=20:80 to I:II=95:5, and in particular from I:II=30:70 to I:II=95:5.
According to the invention, the film comprises a UV stabilizer and a flame retardant. The UV stabilizer is advantageously fed by way of what is known as masterbatch technology directly during film production, the concentration of the UV stabilizer here preferably being from 0.01 to 5% by weight, based on the weight of the layer of the crystallizable thermoplastic.
According to the invention, the flame retardant is likewise fed by way of what is known as masterbatch technology directly during film production, the concentration here being from 0.5 to 30% by weight, preferably from 1 to 20% by weight, based on the weight of the layer of the crystallizable thermoplastic.
Light, in particular the ultraviolet content of solar radiation, i.e. the wavelength region from 280 to 400 nm, causes degradation in thermoplastics, the results of which are not only a change in appearance due to color change or yellowing but also an adverse effect on mechanical and physical properties.
The suppression of this photooxidative degradation is of considerable industrial and economic importance, since without it many thermoplastics have drastically reduced scope of application.
The absorption of UV light by polyethylene terephthalates, for example, starts below 360 nm, increasing markedly below 320 nm, and is very pronounced below 300 nm. Maximum absorption occurs at between 280 and 300 nm.
In the presence of oxygen it is mainly chain cleavage which is observed, but without any crosslinking. The predominant photooxidation products in quantity terms are carbon monoxide, carbon dioxide and carboxylic acids. Besides direct photolysis of the ester groups, attention has to be paid to oxidation reactions which proceed via peroxide radicals, again to form carbon dioxide.
In photooxidation of polyethylene terephthalates there can also be cleavage of hydrogen at the position a to the ester groups, giving hydroperoxides and decomposition products of these, and this may be accompanied by chain cleavage (H. Day, D. M. Wiles, J. Appl. Polym. Sci. 16 [1972] p. 203).
UV stabilizers, i.e. light stabilizers which are UV absorbers, are chemical compounds which can intervene in the physical and chemical processes of light-induced degradation. Carbon black and other pigments can give some protection from light, but these substances are unsuitable for transparent films, since they cause discoloration or color change. For transparent, matt films the only suitable compounds are organic or organometallic compounds which give rise to no, or only extremely slight, color or color change in the thermoplastic to be stabilized, i.e. are soluble in the thermoplastic.
UV stabilizers which are suitable light stabilizers are those which absorb at least 70%, preferably 80%, particularly preferably 90%, of the UV light in the wavelength region from 180 to 380 nm, preferably from 280 to 350 nm. These are particularly suitable if they are thermally stable, i.e. do not decompose, nor cause any evolution of gas, in the temperature range from 260 to 300xc2x0 C. Examples of UV stabilizers which are suitable light stabilizers are 2-hydroxybenzophenones, 2-hydroxybenzotriazoles, organonickel compounds, salicylic esters, cinnamic ester derivatives, resorcinol monobenzoates, oxanilides, hydroxybenzoic esters, sterically hindered amines and triazines, preference being given to the 2-hydroxybenzotriazoles and the triazines.
The film of the invention comprises at least one flame retardant, fed by way of what is known as masterbatch technology directly during film production, the concentration of the flame retardant being in the range from 0.5 to 30.0% by weight, preferably from 1.0 to 20.0% by weight, based on the weight of the layer of the crystallizable thermoplastic. The ratio by weight of flame retardant to thermoplastic usually maintained when producing the masterbatch is in the range from 60:40 to 10:90.
Typical flame retardants include bromine compounds, chloroparaffins and other chlorine compounds, antimony trioxide, and alumina trihydrates, but the halogen compounds are disadvantageous due to the halogen-containing by-products produced. Another extreme disadvantage is the low lightfastness of any film provided with these, and also the evolution of hydrogen halides in the event of a fire.
Examples of suitable flame retardants used according to the invention are organophosphorus compounds, such as carboxyphosphinic acids, anhydrides of these, and dimethyl methylphosphonate. It is important for the invention that the organophosphorus compound is soluble in the thermoplastic, since otherwise compliance with the required optical properties is lacking.
Since the flame retardants generally have some degree of susceptibility to hydrolysis, the additional use of a hydrolysis stabilizer can be advisable.
The hydrolysis stabilizers generally used are phenolic stabilizers, alkali metal/alkaline earth metal stearates, and/or alkali metal/alkaline earth metal carbonates, in amounts of from 0.01 to 1.0% by weight. The amount used of phenolic stabilizers is preferably from 0.05 to 0.6% by weight, in particular from 0.15 to 0.3% by weight, and their molar mass is preferably more than 500 g/mol. Pentaerythrityl tetrakis-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate or 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene is particularly advantageous.
In one particularly preferred embodiment, the film of the invention comprises from 1 to 20% by weight of a flame retardant, such as dimethyl methylphosphonate and from 0.01 to 5.0% by weight of 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol of the formula
or from 0.01 to 5.0% by weight of 2,2-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1,1,2,2-tetramethylpropyl)-phenol) of the formula
In one preferred embodiment, use may also be made of a mixture of these two UV stabilizers, or of a mixture of at least one of these two UV stabilizers with other UV stabilizers, the total concentration of light stabilizer preferably being from 0.01 to 5.0% by weight, based on the weight of crystallizable polyethylene terephthalate.
Besides the flame retardant fed by way of masterbatch technology and the UV stabilizer, the base layer and/or the outer layer(s) may also comprise conventional additives, such as stabilizers and antiblocking agents. They are advantageously added to the polymer or polymer mixture before melting begins. Examples of stabilizers used are phosphorus compounds, such as phosphoric acid or phosphoric esters. Typical antiblocking agents (also termed pigments in this context) are inorganic and/or organic particles, such as calcium carbonate, amorphous silica, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, lithium fluoride, the calcium, barium, zinc, or manganese salts of the dicarboxylic acids used, carbon black, titanium dioxide, kaolin, or crosslinked polymer particles, such as polystyrene particles or acrylate particles.
Additives selected may also be mixtures of two or more different antiblocking agents, or mixtures of antiblocking agents of the same composition, but with different particle sizes. The usual concentration of the particles may be added to each of the layers, e.g. in the form of a glycolic dispersion during polycondensation or by way of masterbatches during extrusion. Pigment concentrations which have proven particularly suitable are from 0.0001 to 10% by weight. Addition of these particles to the outer layer gives another advantageous opportunity of varying the degree of mattness of the film. Increase in pigment concentration is generally associated with an increase in the degree of mattness of the film. An example of a detailed description of antiblocking agents is found in EP A 0 602 964.
The present invention also provides a process for producing this film. It encompasses
a) producing a film from base and outer layer(s) by coextrusion,
b) biaxial orientation of the film, and
c) heat-setting of the oriented film.
It is important for the invention that the masterbatch which comprises the flame retardant and, where appropriate, the hydrolysis stabilizer is precrystallized or predried. This predrying includes gradual heating of the masterbatch at subatmospheric pressure (from 20 to 80 mbar, preferably from 30 to 60 mbar, in particular from 40 to 50 mbar), with stirring, and, where appropriate, post-drying at constant increased temperature, again at subatmospheric pressure. The masterbatch is preferably charged at ambient temperature from a feed vessel in the required blend together with the polymers of the base and/or outer layers and, where appropriate, with other raw material components batchwise into a vacuum dryer which during the course of the drying or residence time passes through a temperature profile of from 10 to 160xc2x0 C., preferably from 20 to 150xc2x0 C., in particular from 30 to 130xc2x0 C. During a residence time of about 6 hours, preferably 5 hours, in particular 4 hours, the raw material mixture is stirred at from 10 to 70 rpm, preferably from 15 to 65 rpm, in particular from 20 to 60 rpm. The resultant precrystallized or predried raw material mixture is post-dried in a downstream vessel, likewise evacuated, at from 90 to 180xc2x0 C., preferably from 100 to 170xc2x0 C., in particular from 110 to 160xc2x0 C., for from 2 to 8 hours, preferably from 3 to 7 hours, in particular from 4 to 6 hours.
To produce the outer layer of the invention, it is advantageous to feed pellets of mixture component I and pellets of mixture component II in the desired mixing ratio directly to the extruder, where appropriate together with the flame retardant masterbatch which has been predried. It has proven advantageous for extrusion of the matt outer layer of the invention to use a twin-screw extruder, e.g. as described in EP 0 826 478. The materials can be melted and extruded at about 300xc2x0 C. with a residence time of about 5 min. Under these conditions, transesterification reactions can proceed in the extruder, and these can form other copolymers from the homopolymers and the copolymers.
The polymers for the base layer are advantageously fed by way of another extruder, together with the flame retardant masterbatch, which has been predried. Any foreign bodies or contamination present may be filtered out from the polymer melt prior to extrusion. The melts are then extruded through a coextrusion die to give flat melt films and laminated to one another. The multilayer film is then drawn off and solidified with the aid of a chill roll and, where appropriate, other rolls.
The biaxial orientation is generally carried out sequentially or simultaneously.
In sequential stretching, it is preferable to orient first longitudinally (i.e. in machine direction) and then transversely (i.e. perpendicularly to machine direction). This leads to orientation of the molecular chains. The longitudinal orientation can be carried out with the aid of two rolls running at different speeds corresponding to the desired stretching ratio. For transverse orientation use is generally in the range made of an appropriate tenter frame. In simultaneous stretching the film is simultaneously stretched longitudinally and transversely in a tenter frame.
The temperature at which the orientation is carried out may vary within a relatively wide range and depends on the desired properties of the film. The longitudinal stretching is generally carried out at from 80 to 130xc2x0 C. and the transverse stretching at from 90 to 150 C. The longitudinal orientation ratio is generally in the range from 2.5:1 to 6:1, preferably from 3:1 to 5.5:1. The transverse stretching ratio is generally in the range from 3.0:1 to 5.0:1, preferably from 3.5:1 to 4.5:1. If desired, the transverse stretching may be followed by another longitudinal orientation, and even by another transverse orientation.
In the heat-setting which follows, the film is held at a temperature of from 150 to 250xc2x0 C. for from 0.1 to 10 s. The film is then wound up in the usual way.
One or both surfaces of the film may therefore have a coating. The thickness of this coating on the finished film is from 5 to 100 nm, preferably from 20 to 70 nm, in particular from 30 to 50 nm. It is preferably applied in-line, i.e. during the film-production process, advantageously prior to transverse orientation. Application by reverse gravure roll coatings is particularly preferred, and this process permits extremely uniform application of the coating at the layer thickness mentioned. The coatings are appliedxe2x80x94preferably by aqueous methodsxe2x80x94as solutions, suspensions, or dispersions, and provide the film surface with additional functionality, for example making the film sealable, printable, metallizable, sterilizable, antistatic, or improving its aroma barrier for example, or permitting its adhesion to materials which would not otherwise adhere to the film surface (e.g. photographic emulsions). Examples of substances or compositions which provide additional functionality are:
Acrylates, as described by way of example in WO 94/13476, ethylene-vinyl alcohols, PVDC, waterglass (Na2SiO4), hydrophilic polyesters (PET/IPA polyesters containing the sodium salt of 5-sulfoisophthalic acid, for example as described in EP-A-0 144 878 or U.S. Pat. No. 4,252,885 or EP-A-0 296 620), vinyl acetates, for example as described in WO 94/13481, polyvinyl acetates, polyurethanes, the alkali metal or alkaline earth metal salts of C10-C18 fatty acids, and butadiene copolymers with acrylonitrile or methyl methacrylate, methacrylic acid, acrylic acid, or esters thereof.
The compositions or substances mentioned are applied in the form of dilute, preferably aqueous, solution, emulsion, or dispersion to one or both surfaces of the film. The solvent is then evaporated. If the coatings are applied in-line prior to transverse stretching, the heat treatment during transverse stretching and subsequent heat-setting is usually sufficient to evaporate the solvent and dry the coating. The dried coatings then have the abovementioned desired layer thicknesses.
The films may also be coatedxe2x80x94preferably in an off-line processxe2x80x94with metals, such as aluminum, or with ceramic materials, such as SiOx or AlxOy. This in particular improves their gas-barrier properties.
The polyester film of the invention preferably also comprises a second outer layer C. The structure, thickness, and composition of the second outer layer may be selected irrespective of the other outer layer present, and the second outer layer may likewise comprise the abovementioned polymers, the UV stabilizer, the flame retardant, or polymer mixtures for the base layer or the first outer layer of the invention, but these do not have to be identical with those of the first outer layer. The second outer layer may also comprise other commonly used outer layer polymers, while these may also be provided with UV stabilizer and/or the flame retardant.
If desired, there may also be an intermediate layer between the base layer and the outer layer(s). The intermediate layer may be composed of the polymers described for the base layer. In one particularly preferred embodiment, it is composed of the polyester used for the base layer. It may also comprise the conventional additives described, and the flame retardant and/or the UV stabilizer. The thickness of the intermediate layer is generally above 0.3 xcexcm, preferably in the range from 0.5 to 15 xcexcm, in particular from 1.0 to 10 xcexcm.
The thickness of the outer layer(s) is generally above 0.1 xcexcm, preferably in the range from 0.2 to 5 xcexcm, in particular from 0.2 to 4 xcexcm, and the thicknesses of the outer layers may be identical or different.
The total thickness of the polyester film of the invention may vary within wide limits and depends on the intended application. It is preferably from 4 to 500 xcexcm, in particular from 5 to 450 xcexcm, with preference from 6 to 300 xcexcm, the base layer preferably making up from about 40 to 90% of the total thickness.
It is entirely surprising that the use of the abovementioned UV stabilizers in films led to the desired result. The skilled worker would probably first have attempted to achieve UV resistance by using an antioxidant, but would have discovered that on weathering the film rapidly yellows.
On using conventional UV stabilizers, the skilled worker would have found that
the UV stabilizer has inadequate thermal stability and at temperatures of from 200 to 240xc2x0 C. decomposes and evolves gases
large amounts of UV stabilizer would have had to have been incorporated (from about 10 to 15% by weight) to absorb the UV light and prevent damage to the film.
At these high concentrations, the skilled worker would have found that the film becomes yellow just after it has been produced, with Yellowness Index deviations (YI) around 25. The mechanical properties of the film would also have been found to be adversely affected. Orientation would have produced exceptional problems, such as
break-offs due to unsatisfactory strength, i.e. modulus of elasticity too low;
die deposits, causing profile variations;
roller deposits from the UV stabilizer, causing immpairment of optical properties (poor haze, defective adhesion, non-uniform surface);
deposits in stretching frames or heat-setting frames, dropping onto the film.
It was therefore more than surprising that even low concentrations of the UV stabilizer of the invention achieve excellent UV protection. It was very surprising that, together with this excellent UV protection:
within the accuracy of measurement, the Yellowness Index of the film is unchanged from that of an unstabilized film;
there were no evolution of gases, no die deposits, and no frame condensation, and the film therefore has excellent optical properties and excellent profile and layflat;
the UV-resistant film has excellent stretchability, and can therefore be produced in a reliable and stable manner on high-speed film lines at speeds of up to 420 m/min.
It was also surprising that a flame-retardant film with the required property profile can be produced cost-effectively and without caking in the dryer by using masterbatch technology and suitable predrying and/or precrystallization and, where appropriate, small amounts of a hydrolysis stabilizer, and that the film does not embrittle by exposure to heat and does not break when folded.
It is moreover very surprising that it is also possible to reuse the recycled material (regrind) produced from the films without adversely affecting the Yellowness Index of the film.
The film of the invention can readily be recycled without pollution of the environment, and is therefore suitable for use as short-lived advertising placards, in the construction of exhibition stands, or for other short-lived promotional items, where fire protection and UV absorption are desired.
Another advantage is that the production costs of the film of the invention are only slightly higher than those for a film made from standard polyesters. The other properties of the film of the invention relevant to its processing and use are substantially unchanged or indeed have been improved. In addition, it has been ensured that during production of the film it is possible to reuse the regrind in a proportion of up to 50% by weight, preferably from 10 to 50% by weight, based in each case on the total weight of the film, without any significant resultant adverse effect on the physical properties of the film.
In summary, the film of the invention has flame retardancy to DIN 4102 (construction materials classes B1 and B2), is impermeable to UV light, is highly UV resistant, has low gloss, in particular low gloss on film surface A, and has comparatively low haze. It moreover has good winding and processing performance. It is also worthy of mention that the outer layer of the invention has good writability with respect to ballpoint pen, felt-tip pen, or fountain pen.
The gloss of film surface A is lower than 70. In one preferred embodiment the gloss of this side is less than 60, and in one particularly preferred embodiment less than 50. This surface of the film is therefore particularly effective for promotional purposes.
In addition, the film complies with construction materials classes B1 and B2 to DIN 4102 Part 1 and Part 2 and shows no embrittlement on exposure to heat. The Yellowness Index (YI) of the film of the invention is not higher than that of a standard film. The film begins to transmit light or radiation at  greater than 360 nm, i.e. the film absorbs the harmful UV radiation. A non-UV-resistant film transmits radiation from as low as 280 nm, i.e. the UV light in the wavelength region from 280 to 360 nm is not absorbed but transmitted by the film.
The haze of the film of the invention is smaller than 40%. In one preferred embodiment, the haze of the film is less than 35%, and in one particularly preferred embodiment less than 30%. The comparatively low haze of the film (compared with a matt monofilm, see comparative example) means that the film can, for example, be reverse-printed, or viewing windows can be incorporated through which, for example, the contents can be clearly discerned.
The combination of exceptional properties gives the film of the invention excellent suitability for a wide variety of applications, for example for interior decoration, for construction of exhibition stands or for exhibition requisites, as displays, for placards, for protective glazing of machinery or vehicles, in the lighting sector, in the fitting out of shops or of stores, as a promotional item, or laminating medium, for greenhouses, roofing systems, exterior cladding, protective coverings, applications in the construction sector, and illuminated advertising profiles, blinds, and electrical applications.
Other application sectors are its use for producing labels, as a release film, or as a hot-stamping foil, or in-mold labeling.
The table below (Table 1) gives again the most important film properties of the invention.
The methods used to characterize the polymers and the films were as follows:
Test Methods
DIN=Deutsches Institut fxc3xcr Normung
ISO=International Organization for Standardization
ASTM=American Society for Testing and Materials
SV (DCA), IV (DVE)
Standard viscosity SV (DCA) is measured in dichloroacetic acid by a method 30 based on DIN 53726.
Intrinsic viscosity (IV) is calculated as follows from standard viscosity
IV(DCA)=6.67xc2x710xe2x88x924SV(DCA)+0.118
Coefficient of Friction
Coefficient of friction is determined to DIN 53 375, 14 days after production.
Surface Tension
Surface tension was determined by what is known as the ink method (DIN 53 364).
Haze
Haze of the film was measured to ASTM D1003-52. The Hxc3x6lz haze measurement was made by a method based on ASTM D1003-52, but in order to utilize the ideal measurement range was measured on four mutually superimposed laps of film, and a 1xc2x0 slit diaphragm was used instead of a 4xc2x0 pinhole.
Gloss
Gloss was determined to DIN 67 530. Reflectance was measured, this being an optical value characteristic of a film surface. Based on the standard ASTM D523-78 and ISO 2813, the angle of incidence was set at 20 or 60. A beam of light hits the flat test surface at the set angle of incidence and is reflected and/or scattered by the surface. A proportional electrical variable is displayed representing light rays hitting the photoelectric detector. The value measured is dimensionless and must be stated together with the angle of incidence.
Roughness
The roughness Ra of the film was determined to DIN 4768 with a cutoff of 0.25 mm.
Mechanical Properties
Modulus of elasticity and tensile strength at break, and tensile strain at break, were measured longitudinally and transversely to ISO 527-1-2.
Weathering (Bilateral), UV Resistance
UV resistance was tested as follows to the ISO 4892 test specification:
Numerical values of  less than 0.3 can be disregarded and mean that no significant color change has occurred.
Yellowness Index
Yellowness Index (YI) is the deviation from colorlessness in the xe2x80x9cyellowxe2x80x9d direction and is measured to DIN 6167. Yellowness Indices (YIs) less than 5 are not visually detectable.
Each of the examples and comparative examples below concerns transparent films of varying thickness, produced on the extrusion line described.
All of the films were weathered bilaterally, each for 1000 hours per side, to the test specification ISO 4892 using the Atlas C165 Weather-Ometer, and then tested for mechanical properties, Yellowness Index (YI), surface defects, light transmittance, and gloss.
The examples below provide illustration of the invention.

Matt, UV stable, flame-retardant co-extruded polyester film, a method for the production thereof and the use of the same


A throat section of a venturi for passing a flow of fluid therethrough comprises a plurality of spaced parallel physical barriers. The physical barriers are oriented parallel to the direction of fluid flow through the throat section. The throat section is installed in a throat zone of a venturi scrubber defined by an upstream zone having an unobstructed upstream section, a throat zone having the throat section, and a downstream section. The spaces between adjacent barriers are from about 3/16 inches to about 8 inches so as to create free stream zones between adjacent barriers. Each barrier may have a selected length which decreases with distance from the axis of the throat section. A method for treating a stream of effluent fluid containing entrained particulates by introducing the effluent fluid and target droplets into the throat section so as to promote impaction therebetween is also described.

Venturi devices comprise a duct or pipe providing a fluid flow passageway that decreases progressively in cross-sectional area in an "upstream section" to a minimum at a "throat section," and then increases progressively again in a "downstream section." Fluid forced through the venturi device has its flow velocity increased progressively in the upstream section to reach a maximum at the throat, the velocity decreasing again in the downstream section, usually accompanied by a considerable turbulence of the fluid in the downstream section and in the duct- or pipe-work fed from the device. The passage of fluid through the device is accompanied by a pressure drop therein, the value of which is proportional to the amount of energy or power required to pass the fluid therethrough. It is usually one of the main endeavors of designers of these devices to keep this pressure drop as low as possible, so that the device and the apparatus in which it is incorporated will operate at maximum efficiency and minimum external power requirements.
In a typical gas scrubbing device such as a venturi scrubber, a gas cleaning liquid (e.g., water) is injected into an incoming particle- or particulate-laden gas stream at or very close to the entrance to the venturi throat, where the gas cleaning liquid is immediately atomized by the high-velocity gas stream into a spray or mist droplets. This mist or spray has a high probability of coming into physical contact with solid material mixed in with the gas stream. This high probability results chiefly from the difference in velocity between the slower moving mist droplets, typically called "target droplets," and the faster moving gas-borne particulates. This high contact probability is also enhanced by the above-mentioned turbulence in the gas downstream of the throat. The liquid droplets pick up the particulate matter after which the droplets holding the particulate material are removed from the stream and collected. A centrifugal entrainment collector is typically employed for receiving and removing the particulate-laden droplets.
The overall collection efficiency of a venturi scrubber is highly dependent on the throat velocity or pressure drop, the liquid-gas-ratio, the chemical wettability of the particulate, and the energy expended to create the target droplets.
The overall effectiveness of the venturi scrubber is a direct function of the percentage of particulates removed from the incoming particulate-laden gas stream. Since the particulates are captured mainly by attaching themselves to target droplets, a major concern in the design of a venturi scrubber is to allow for maximum probability of interaction between target droplets and the particulate-laden gas stream while the gas stream flows through the throat of the venturi scrubber.
In a conventional venturi scrubber, a particulate bearing carrier gas is caused to accelerate when it is forced to pass through a restriction in the containing ductwork (venturi throat). The static pressure of the slow moving gas stream is converted to velocity pressure in the restriction as the gas velocity increases.
Conventional venturi theory holds that the velocity pressure of the carrying gas stream shears the liquid which is administered into the gas stream into fine droplets. The shearing action comes from the differential in velocity of the gas stream relative to the liquid. The size of the resulting droplet created is related to various venturi scrubber physical parameters such as relative velocity, liquid surface tension and viscosity, carrier gas density and viscosity, gas/liquid temperatures, liquid to gas ratio, and other factors.
The target droplets in most of the mathematical models are assumed to be flowing as individual droplets in the gas stream. The particulates, depending upon their size, either flow along streamlines in the gas flow or move through the carrier gas as dictated by thermophoretic, or diffusiophoretic forces.
Generally speaking, the smaller the droplet and the greater the density of droplets per unit volume, the smaller the particle that can be collected. Smaller droplets, given their radius of curvature and reduced surface tension, are assumed to be easier to penetrate. The size of the droplets created is primarily related to scrubber pressure drop.
Equations were developed to predict this pressure drop from certain known operating parameters. Particulate removal efficiencies, however, always seem to be overly optimistic when using the common mathematical models. In other words, either the "real-world" venturi scrubbers had inherent inefficiencies built into them, or the models were wrong. An implication of the results could be that the mechanism for droplet creation could be improved. Another implication could be that the droplets, once created, were not being used properly.
The conventional venturi theory contends that the shearing action in the restricted throat zone creates the droplets. The target droplets in the free stream zone of the throat (the area at or near the center of the throat) would most closely follow the model, but those at or near the throat wall (where local velocities are lower) would not. When the throat zone ended and the venturi section enlarged, the gases and the "large" liquid droplets in the free stream zone would slow down rapidly but the smaller particulate given their smaller size, would continue on their course. The particulate would impact into the slower target droplet and thereby be captured. The smaller particles (below about 0.3 microns) would exhibit little inertia (given their low mass) and would instead by captured by diffusion or interception.
When clear venturi scrubber models were built, however, it was evident that the gas velocity through the typical venturi scrubber throat varied considerably with throat width. Near the wall, the liquid formed a thin stream of liquid with very few droplets and therefore low efficiency. As one moved towards the higher velocities in the center of the throat (free stream area), greater numbers of smaller droplets were created. It is in this center region that the particulate capture models would seem to truly apply. If one could create a throat having a uniform free stream area, with concentrated zones of very small droplets, the capture should improve and more closely follow the mathematical model.
Over the decades that venturi scrubbers have been in use, widely varying throat designs have been tried in an attempt to maximize the scrubber performance.
Attempts have been made to improve recovery efficiency in a venturi throat by placing an obstruction in the throat zone. U.S. Pat. No. 4,023,942 describes a double diamond insert that separates the gas flow through the throat zone into a pair of diverging, constant cross-section throats. The double diamond insert is adjustable so as to be positionable in selected vertical locations within the venturi passage. A similar type of insert is disclosed in U.S. Pat. Nos. 4,049,399, 4,337,229, 3,957,464 and 3,969,482. One disadvantage of the diamond shape is that it creates skewed paths, thereby increasing the complexity of the gas flow path. The inclined angle of the velocity zone (the throat zone) has further disadvantages. In practice, the water target droplets try to move straight downward, impacting on the movable throat section, and causing excess pressure drop. Also, the inclined angle promotes angled collisions between target droplets and gas-entrained particles. Since maximum kinetic energy transfer occurs when the particle directly impacts the center of the droplet, the angled throat does not promote desired direct impact collisions of target droplets and particles.
U.S. Pat. No. 3,870,082 discloses the placement of a plurality of flat parallel physical barriers within a venturi-type device. Although the barriers traverse the venturi throat section, all of the barriers deliberately extend into both the upstream section and the downstream section. In fact, by using barriers of progressively different lengths, the leading and trailing edges of the barriers themselves form the required upstream and downstream sections. For example, the upstream section in U.S. Pat. No. 3,870,082 encompasses the area defined by the leading edges of plates 27 and 28 that extend beyond the shortest plates 29, as depicted in FIG. 1. In this manner, plates 27 and 28 both form and obstruct the upstream section. Within the venturi throat section, all of the barriers have identical lengths. U.S. Pat. No. 3,870,082 teaches that the preferred spacing between the parallel physical barriers is between 5 to 15 times the maximum size of particle that is to be removed by the device. In an exemplary embodiment, a spacing of 0.016 inches (approximately 1/64 of an inch) is employed. U.S. Pat. No. 3,870,082 further discloses that with the preferred spacings the gas flow between the plates is in the form of two back-to-back turbulent boundary layers between two immediately-adjacent liquid films, as illustrated in FIG. 5 of this patent. As described in U.S. Pat. No. 3,870,082, this effect leads to a very high probability that the particles will be trapped by the liquid film and removed from the air stream. Thus, it should be evident that the parallel plate design, as depicted in FIG. 5 of this patent, is not designed to create or employ any free stream zones. Particle capture is mainly performed by the effects of the back-to-back turbulent boundary layers.
In U.S. Pat. No. 3,870,082, a scrubbing liquid is sprayed out from nozzles 23 or 24. As depicted in FIG. 5 of this patent, the liquid runs down the surfaces of the physical barriers to provide thin films 32 thereon. The thin films of liquid are contacted by a particle-laden gas stream (e.g., furnace exhaust gases) which passes between adjacent barriers as the two back-to-back turbulent boundary layers mentioned above. The thin films 32 of liquid capture the particles and carry them away as the liquid trickles down along the surfaces of the physical barriers.
The physical barriers disclosed in U.S. Pat. No. 3,870,082 are also employed in U.S. Pat. No. 4,000,993.
U.S. Pat. No. 4,140,501 discloses a wet gas scrubber having a multiple-throat venturi section. The venturi section comprises three modular venturi units arranged side-by-side for the flow of the air stream therethrough in parallel. Each module comprises a plurality of vertically disposed rods arranged in a plane transverse to the direction of flow of the air stream in spaced-apart relationship. The rods may be, for example, one-inch pipes spaced apart to leave one inch venturi throats between adjacent pipes. In U.S. Pat. No. 4,140,501, length of the venturi throat will necessarily be limited by the diameter of the rods. The throat lengths in the disclosed embodiment will be very short (e.g., one inch) thereby providing only a very small area for particle impaction and capture. The extremely short throat distance does not permit the liquid particles to have any meaningful residence time within the throat zone. Thus, there can be no meaningful mixing of the incoming gas stream with the liquid particles so as to encourage impaction and collection of particulate matter entrained in the incoming gas stream. The venturi throat in U.S. Pat. No. 4,140,501 is probably more accurately characterized as a narrow orifice contactor, as opposed to a venturi.
U.S. Pat. No. 4,012,469 discloses a wet gas scrubber having a throat region comprising an upper and lower row or tray of tubular scrubber rods. The rods are spaced in relation to each other in the direction of the gas flow and are in a parallel relation with one another. The upper rods are connected to a fluid distribution system and have openings in the tube walls for providing wash liquid. The wash liquid (e.g., water droplets) exits the tube walls countercurrent to the incoming gas flow. The incoming gas with foreign particles and liquid droplets entrained therein passes through several venturis formed between the rods of the upper row and the rods of the lower row, thereby causing an increase in velocity. During the traversal of the gas through these venturis, the water droplets are broken up into smaller sizes depending on the velocity of the gas and the resulting drag forces and intimate contact between the particulate matter and the water droplets is produced. There thus results an agglomeration action in the venturi. In U.S. Pat. No. 4,012,469, the lower row of rods is vertically adjustable so as to, in effect, form adjustable venturis between the two rows of rods. In other words, the lower row of rods move up and down perpendicular to the gas flow. The lower row of rods, however, never rise up between the upper tubes and assume the same location, on the same plane. In operation, the lower tubes act like baffles.
In spite of extensive research and exhaustive attempts to improve the performance of venturi scrubbers, there is still a need for further improvements which increase particle capture without significantly affecting the pressure drop, and thereby the amount of energy required to pass the fluid therethrough. There is also still a need for venturi throat inserts which are simple to fabricate, which do not significantly alter the incoming path flow of gas as it passes therethrough and which promotes direct impact collisions between target droplets and particles. The present invention fills that need.

Multiple throat, narrow gap venturi scrubber and method of using same