Flat multiplayered laser-optical recording material.

The invention relates to a new, sheet-like, multilayer, laser-optical recording material with improved application properties<ul id="ul0001" list-style="none"><li>a) one or more layers of an optically clear and isotropic, homogeneous, orientation-refractive mixture of poly (2,6-dimethylphenylene ether) (PPE) with a styrene polymer as a carrier and</li><li>b) at least one amorphous, thermally changeable recording layer.</li></ul>

Recording materials of this type are known for example from US-A-4 373 065 or EP-A-225 801.

In the context of this invention, the term "areal" includes all spatial forms whose thickness is considerably smaller than their length and width. Accordingly, the recording materials can be in the form of tapes, disks or disks, the disks being generally also referred to as data disks or disks.

The term "amorphous" indicates that the material of the recording layers (b) has no crystalline regions which are larger than the thermally changed regions, but that it is optically isotropic in this order of magnitude.

Digital data are written into the recording layers (b) of recording materials of the type in question with the aid of pulse-modulated writing laser beams in the form of thermally changed areas. The writing laser beams are focused on the recording layers (b) and / or hit them perpendicularly. Continuous wave lasers can also be used to write analog data. In the case of recorded digital data, the thermally changed areas of the recording layers (b) have a round or elliptical base area. In the case of analog data, the thermally changed areas are of any base area.

For reading the data, use is generally made of continuously emitted reading laser beams (continuous wave laser beams) whose energy is insufficient to cause further changes in the recording layers (b). The reading laser beams are also focused on the recording layers (b) and / or hit them vertically. During the reading process, the light reflected from the recording layers (b) is generally detected with the aid of suitable optical arrangements, supplied to conventional and known detectors and converted into signals by suitable electronic devices.

These writing and reading methods and the corresponding recording materials suitable for this purpose are therefore generally designated with the term "laser-optical", with the writing and reading methods generally being subsumed under the term "data recording".

The thermally modified areas of the recording layers (b) can have the shape of holes which penetrate the recording layer entirely. In this case, one speaks generally of ablative laser-optical data recording. When reading out the data with a reading laser beam, the different reflectivity of the holes and the unchanged areas of the recording layer (b) are used. In order to achieve a high sensitivity and a high signal-to-noise ratio, a reflector layer can be used, which is exposed by the hole formation and reflects the reading laser beam particularly strongly.

The thermally changed areas can also have the shape of craters (pits), which may have a clean crater rim (wall). In this case, one speaks of deformative laser-optical data recording. The data on the diffraction of the light from the reading laser beam are read out on the craters.

The thermal change can, however, also result in areas in which no ablation or deformation, but a phase transformation of the material of the recording layer into another material modification has taken place. In such a case, one speaks of laser-optical data recording by phase conversion. In general, the phase change lowers the reflectivity in the areas described and / or increases the light transmission. However, the opposite effect may also occur under certain circumstances, ie the reflectivity is increased and / or the light transmission is reduced. In general, the areas thermally changed in this way are referred to as spots.

The recording layers (b) can, however, also be underlaid with layers which expand when irradiated or develop gases, as a result of which the recording layers (b) are locally stretched. In this way, relief structures are formed in the surface of the recording layers (b), which contain the written data.

However, the gases can also be released in the recording layers (b) even with the formation of small light-scattering bubbles. This is commonly called vesicular data logging.

In addition, a chemical reaction of one component or a chemical reaction between several components of the recording layers (b) may have taken place in the thermally changed regions, as a result of which the optical properties of the recording layers (b) in these regions have been changed.

A local change in the reflection of recording layers (b) during irradiation can, however, also be achieved by enlarging or melting together small particles. These small particles, for example gold granules, can be embedded in a matrix. But it can also be metal-coated plastic beads. Recording layers (b) which consist of these beads have an extremely low basic reflectivity and are generally referred to as "moth eye layers".

Last but not least, the thermally changed areas in recording layers (b), which consist of amorphous, ferrimagnetic layers magnetized perpendicular to their surface, can have the form of spots which have a direction of magnetization opposite to the original direction. These "spots" arise when the ferrimagnetic material of these layers is heated by a laser beam under the influence of an applied magnetic auxiliary field: the heating increases the coercive field strength H_c of the ferrimagnetic material. It falls below the coercive force H_c at a critical temperature depending on the material used, the field strength of the applied magnetic auxiliary field, the area in question is magnetized.

To read these areas, linearly polarized light from a continuously emitting continuous wave laser is used, the light output of which is not sufficient to heat the material above the critical temperature. This laser beam is reflected either by the recording layer (b) itself or by a reflection layer arranged behind it, with an interaction between the magnetic moments in the recording layer (b) and the magnetic vector of the laser light wave. This interaction makes the plane of polarization<img file="EP0303209A2_D0001.tif" /> of the laser light, which is reflected by a "spot" or by a reflection layer behind it, is rotated by a small angle with respect to the original plane. This rotation of the plane of polarization happens<img file="EP0303209A2_D0002.tif" /> when the light is reflected on the recording layer (b) itself, this is referred to as the Kerr effect and the angle of rotation accordingly as the Kerr angle of rotation; if, on the other hand, the plane is rotated when the light passes through the recording layer twice, one speaks of the Faraday effect and the Faraday rotation angle.

This rotation of the plane of polarization <img file="EP0303209A2_D0003.tif" /> The laser light reflected from the recording material can be measured with the aid of suitable optical and electronic devices and converted into signals.

Recording layers (b) of this type are therefore generally designated with the term "magneto-optical".

In the case of multilayer, laser-optical data disks and also in the case of the known audio and video compact disks, the usual and known disk drives are generally used for writing and / or reading digital data. Such a disk drive essentially contains a turntable and a laser-optical read and write head, as well as mechanical servo devices for correcting the tracking, autofocusing devices, optical elements for analyzing tracking and autofocus errors, detector devices with upstream optical components for detecting the light reflected from the data disks the reading laser beam and suitable electronic components. A laser-optical read and write head usually contains laser diodes, which emit infrared light and consist of semiconductor materials such as GaAlAs. In addition, such a read and write head generally also has other suitable optical components, such as dielectric beam splitters, polarization beam splitters or polarization-independent beam splitters, and a λ / 4 or λ / 2 plate.

In general, the known laser-optical recording materials contain a dimensionally stable support which, in the case of laser-optical data disks or in the known audio and video compact discs, usually has a 1.2 mm thick, 83 to 350 mm diameter, optically clear disk made of a plastic or a plastic mixture is. Here come as plastics for example Polycarbonate, polymethyl methacrylate, polymethylpentene, cellulose acetobutyrate or mixtures of poly (vinylidene fluoride) and polymethyl methacrylate. Carriers of this type, however, have serious disadvantages, such as an orientation coefficient that is too high (orientation birefringence), a processing temperature that is too high, a heat resistance that is too low, a modulus of elasticity that is too low, a hardness that is too low or water absorption that is too high. Depending on the plastic or plastic mixture used, these disadvantages are more or less common; none of the known materials has an optimal property profile.

If, however, the dimensionally stable support corresponds to a layer (a) of the laser-optical recording material known from US Pat. No. 4,373,065, many of the disadvantages mentioned generally no longer occur. Such a layer (a), which consists of poly (2,6-dimethylphenylene ether) (PPE) and polystyrene, is optically clear and isotropic, homogeneous, free of orientation birefringence, heat-resistant and mechanically stable. In addition, their water absorption is low. This property profile of layer (a) is retained when it is used as a carrier.

Nevertheless, these carriers have disadvantages which prevent their use in practice. The processing temperature of the known polystyrene-PPE mixtures is undesirably high due to their low flowability. If one tries to remedy this by lowering the PPE content and / or by lowering the molecular weight of the polystyrene, this is again a disadvantage, such as an increased orientation birefringence, a reduced modulus of elasticity or a low solvent resistance. Laser-optical recording materials which contain such carriers often have a widely varying signal-to-noise ratio with the same type of recording layer (b). In addition, the retrieval of the written data is frequently disturbed in an unpredictable manner, ie the so-called "tracking" behavior of such recording materials is unsatisfactory and is insufficient for the practice for which quick access to the data is essential. Even with the carrier materials known from EP-A-225 801 made of PPE-polystyrene mixtures, which are said to contain a comparatively low molecular weight PPE in order to lower the processing temperature, these disadvantages are not completely eliminated and the existing problems are not yet fully solved.

The object of the present invention is to find a new, sheet-like, laser-optical recording material which no longer has the disadvantages of the prior art.

Accordingly, a new, sheet-like, multilayer, laser-optical recording material was developed<ul id="ul0002" list-style="none"><li>a) one or more layers of an optically clear and isotropic, homogeneous, orientation-refractive mixture of poly (2,6-dimethylphenylene ether) (PPE) with a styrene polymer as a carrier and</li><li>b) at least one amorphous, thermally changeable recording layer</li></ul> found, which is characterized in that the layer (a) forming the dimensionally stable support a₁) has one or two structured surfaces, the structures being in the micrometer and / or submicron range, and from such a PPE, at least one styrene polymer and optionally a mixture containing additives, in which the PPE content is in the range from 25 to 45% by weight, based on the mixture, lies and in the a₂) the proportion of the mixture which is not PPE, based on this proportion (a₂), a₂₁) 0.1 to 8% by weight of cyanoethylene groups and / or a₂₂) 1 to 60% by weight of 1-methyl-1-phenylethylene groups and / or a₂₃) 1 to 60 wt.% Of 4'-methylphenyl-ethylene groups and / or a₂₄) 0.01 to 10 wt.% Of groups of the general formula I.<chemistry id="chem0001" num="0001"><img file="EP0303209A2_D0004.tif" /></chemistry> wherein R¹ represents a hydrogen atom or a methyl radical and R² represents a C₁ to C₁₀ alkyl, C₅ to C₈ cycloalkyl or a C₆ to C₁₀ aryl radical, contains, with the proviso that a₂₅) irrespective of whether one or more of the groups (a₂₁) to (a₂₄) and, in addition, possibly also additives are contained in (a₂), the proportion (a₂) in any case has a phenylethylene group content of not less than 40% by weight having.

An essential component of the recording material according to the invention is the layer (a) forming the dimensionally stable support, which is also referred to below simply as "support (a) to be used according to the invention" or simply "support (a)".

The carrier (a) to be used according to the invention has one or two structured surface (s) (a 1). These surfaces (a 1) face the one or more recording layers (b). Carriers (a) which have only one structured surface (a 1) are preferred.

The structures in the surface (a₁) are in the micrometer and / or submicron range. They serve the exact guidance of the reading laser beam and ensure a quick and precise response of the tracking servo and autofocusing devices in the laser optical read and write heads of the disk drives, ie they enable or improve the "tracking". In addition, these structures themselves can contain or represent data, as is the case, for example, with the known audio or video compact disks, or they can be used to encode the written data. The structures usually consist of raised parts and / or recesses. These are in the form of continuous concentric or spiral ruts or isolated hills and / or holes. In addition, the structure can have a more or less smooth wave shape. The ruts are preferred. In their transverse direction they have a rectangular sawtooth, a V-shaped or a trapezoidal contour. Their depressions are generally referred to as "grooves" and their raised parts as "land". Track grooves with 50 to 200 nm deep and 0.4 to 0.8 µm wide "grooves", between which there is a 1 to 3 µm wide "land", are particularly advantageous.

The mixture which builds up the carrier (a) according to the invention contains, based on the mixture, 25 to 45% by weight, preferably 32 to 42% by weight and in particular 34 to 40% by weight, poly (2,6-dimethylphenylene ether) (PPE). The intrinsic viscosity of the PPE is generally in the range from 0.5 to 0.8 dl / g, preferably in the range from 0.5 to 0.7 dl / g (measured at 25 ° C. in chloroform). Methods for the production of PPE are known for example from EP-A-0 161 454.

In addition, this mixture contains a proportion (a₂), which is not PPE. This proportion (a₂) makes up 55 to 75% by weight, preferably 58 to 68% by weight and in particular 60 to 66% by weight, of the mixture.

Particularly advantageous mixtures which are particularly suitable for building up the carrier (a) consist of 34 to 40% by weight of PPE and 60 to 66% by weight of the proportion (a₂).

According to the invention, the portion (a₂) contains polymers which contain copolymerized styrene as an essential constituent, or else the portion (a₂) consists essentially of polystyrene. "Essential" here means a polymerized styrene content in the polymers of the proportion (a₂) of over 40% by weight, which is equivalent to a content of phenylethylene groups of over 40% by weight. This content should not fall below 40% by weight, because otherwise there may be a certain separation of the proportion (a₂) and the PPE over time, which ultimately leads to clouding of the carrier (a) and makes it unusable.

According to the invention contains the portion (a₂) of the mixture of PPE and (a₂) groups (a₂₁), (a₂₂), (a₂₃) and / or (a₂₄), which are used individually or in combination. Regardless of whether one or more of these groups (a₂₁) to (a₂₄) are used, the content of (a₂) in (a₂₅) phenylethylene groups does not fall below 40% by weight; at most it is 40% by weight.

Accordingly, the proportion (a₂) in the mixture which builds the carrier (a) to be used according to the invention can consist of the following combinations of groups or contain these combinations of groups: Phenylethylene + (a₂₁), Phenylethylene + (a₂₁) + (a₂₂), Phenylethylene + (a₂₁) + (a₂₃), Phenylethylene + (a₂₁) + (a₂₄), Phenylethylene + (a₂₁) + (a₂₂) + (a₂₃), Phenylethylene + (a₂₁) + (a₂₂) + (a₂₄), Phenylethylene + (a₂₁) + (a₂₃) + (a₂₄), Phenylethylene + (a₂₁) + (a₂₂) + (a₂₃) + (a₂₄), Phenylethylene + (a₂₂), Phenylethylene + (a₂₂) + (a₂₃), Phenylethylene + (a₂₂) + (a₂₄), Phenylethylene + (a₂₂) + (a₂₃) + (a₂₄), Phenylethylene + (a₂₃), Phenylethylene + (a₂₃) + (a₂₄) and Phenylethylene + (a₂₄).

The combinations of the phenylethylene groups (a₂₅) and the groups (a₂₁), (a₂₂), (a₂₃) or (a₂₄) and the combinations of the phenylethylene groups (a₂₅) and the groups (a₂₂) and (a₂₃) are particularly advantageous.

Of these, the combination of the phenylethylene groups (a₂₅) and the groups (a₂₂) and (a₂₃) is particularly preferred.

The group (a₂₁) is the cyanoethylene group which is derived from the acrylonitrile monomer. If this group alone is contained in (a₂), its amount should not fall below 0.1, preferably 1 and in particular 5% by weight of (a₂). If other groups (a₂₂), (a₂₃) and / or (a₂₄) are used in addition to this group, their amount is 0.1 to 8% by weight. Regardless of whether (a₂₁) is used alone or together with other groups (a₂₂), (a₂₃) and / or (a₂₄), the content of (a₂) in this group should not exceed 8% by weight, because otherwise there is a risk that that then the mixture of (a₂) and PPE segregates.

The group (a₂₂) is the 1-methyl-1-phenyl-ethylene group, which is derived from the monomer α-methylstyrene. If this group is contained in (a₂) alone, its amount should not fall below 1% by weight, preferably 2% by weight and in particular 4% by weight of (a₂) and not exceed 60% by weight of (a₂). It has been shown that an (a₂₂) amount in (a₂) of 1 to 30, preferably 1 to 10 and in particular 3 to 6% by weight is particularly advantageous. If this group is used together with other groups (a₂₁), (a₂₃) and / or (a₂₄), their content in (a₂) is reduced by the amount of the other groups (a₂₁), (a₂₃) and (a₂₁) contained in (a₂) / or (a₂₄), provided that the total amount of groups (a₂₁) to (a₂₄) reaches 60% by weight of (a₂). It is advantageous if the weight ratio of (a₂₂) to the groups (a₂₁) and / or (a₂₄) is greater than 1, provided that these are also used.

The group (a₂₃) is the 4'-methylphenyl-ethylene group, which is derived from the monomer p-methylstyrene. If this group is contained in (a₂) alone, its amount should not fall below 1% by weight, preferably 2% by weight and in particular 4% by weight of (a₂) and not exceed 60% by weight of (a₂). It has been shown that an (a₂₃) amount in (a₂) of 1 to 30% by weight, preferably 1 to 10% by weight and in particular 3 to 6% by weight, is of particular advantage here. If this group is used together with other groups (a₂₁), (a₂₂) and / or (a₂₄), its content in (a₂) is also reduced by the amount of the other groups (a₂₁), (a₂₂) contained in (a₂) and / or (a₂₄), provided that the total amount of groups (a₂₃), (a₂₁), (a₂₂) and / or (a₂₄) reaches 60% by weight of (a₂). It is of particular advantage, however, to use the group (a₂₃) and the group (a₂₂) together. Here, the weight ratio of (a₂₃) to (a₂₂) can vary widely, with the proviso that the (a₂₂) or (a₂₃) amount in the proportion (a₂) is not reduced below 1% by weight.

The group (a₂₄) is a group of the general formula (I) which is derived from acrylic or methacrylic acid esters. Examples of very suitable groups (a₂₄) are the 1-carboxymethyl, ethyl, propyl, i-propyl, n-butyl, tert-butyl, amyl, hexyl, heptyl -, -octyl-, -2'-ethylhexyl-, -nonyl-, -decyl-, -cyclopentyl-, -cyclohexyl-, -2'-methylcyclohexyl-, -2 ', 4'-dimethylcyclohexyl-, -phenyl-, -4'-methyl-phenyl or 1-carboxynaphthyl-ethylene groups or the corresponding 1-methylethylene groups. These highly suitable groups are derived from methyl, ethyl, propyl, i-propyl, n-butyl, sec-butyl, tert-butyl, amyl, hexyl, heptyl, octyl, 2'-ethylhexyl, nonyl, decyl, cyclopentyl, cyclohexyl, 2'-methylcyclohexyl, 2 ', 4'-dimethylcyclohexyl, phenyl, 4'-methylphenyl or the naphthyl ester of acrylic acid or methacrylic acid. The groups (a₂₄) which are derived from the methacrylic acid esters are particularly preferred, of which in turn the 1-carboxy-2'-ethylhexyl, the 1-carboxyphenyl and the 1-carboxy-4'-methylphenyl-1- methylethylene groups are very particularly preferred. These can be used individually or in combination.

If groups (a₂₄) alone are contained in (a₂), their amount should not fall below 0.01% by weight, preferably 1% by weight and in particular 4% by weight, of (a₂) and 10% by weight of (a₂) do not exceed. It is particularly advantageous if the groups (a₂₄) are not used alone but together with the other groups (a₂₁), (a₂₂) and / or (a₂₃). Here, the weight ratio of (a₂₄) to these other groups is in the range of 0.01 to 1, and in particular 0.2 to 1. When this group (a₂₄) is used together with the other groups (a₂₁), (a₂₂) and / or (a₂₃), their share in (a₂) should not exceed the maximum limit of 10% by weight for (a₂) applicable to their individual use exceed and not fall below the relevant lower limit of 0.01% by weight of (a₂).

According to the invention, the groups (a₂₁), (a₂₂), (a₂₃) and / or (a₂₄) in the proportion (a₂) of the carrier (a) constructing mixture of PPE and (a₂) are present as statistically distributed monomer units in the main polymer chains of styrene copolymers . These are statistical copolymers of styrene and the corresponding monomers, as are known per se and can be prepared by radical copolymerization. These statistical copolymers generally have a number average molecular weight <o ostyle="single">M</o>_n from 2 · 10³ to 3 · 10⁵. The copolymers must have the above-mentioned compositions to be used according to the invention. Examples of particularly advantageous statistical copolymers are copolymers prepared by radical copolymerization of - 93 parts by weight of styrene and 7 parts by weight of acrylonitrile; - 95 parts by weight of styrene, 3 parts by weight of acrylonitrile, 1 part by weight of 2-ethylhexyl methacrylic acid and 1 part by weight of phenyl methacrylic acid; - 70 parts by weight of styrene and 30 parts by weight of α-methylstyrene; - 70 parts by weight of styrene and 30 parts by weight of p-methylstyrene; - 60 parts by weight of styrene, 15 parts by weight of α-methylstyrene and 25 parts by weight of p-methylstyrene; or 50 parts by weight of styrene, 45 parts by weight of α-methylstyrene, 3 parts by weight of acrylonitrile and 2 parts by weight of 4′-methylphenyl methacrylic acid, of which the styrene-α-methylstyrene, styrene-p-methylstyrene and the stryol-α-methylstyrene-p-methylstyrene copolymers are very particularly preferred.

According to the invention, the groups (a₂₁), (a₂₂), (a₂₃) and / or (a₂₄) in the proportion (a₂) of the carrier (a) constructing mixture of PPE and (a₂) but also in the form of uniform oligomeric or polymeric blocks from (a₂₁), (a₂₂), (a₂₃) and / or (a₂₄) are present. These blocks can be present as a constituent of styrene copolymers in the polymer main chains of the styrene polymers and / or can be linked as pendant residues to the polymer main chains of the styrene polymers. In this case, it is a question of graft or block copolymers of styrene with acrylonitrile, α-methylstyrene, p-methylstyrene and / or the aforementioned (meth) acrylates. Such graft and block copolymers are known per se and can be prepared by the customary procedures for this. The exact way in which the blocks used are linked to one another can in itself be varied as long as the block and graft copolymers as a whole have the above-mentioned compositions to be used according to the invention. If these compositions are outside the critical limits, the block or graft copolymers in question are unsuitable for the structure of the support (a) to be used according to the invention, regardless of any special type of block linkage that may be present.

It is, however, particularly advantageous according to the invention if in the portion (a₂) of the carrier (a) building mixture of PPE and (a₂) the groups (a₂₁), (a₂₂), (a₂₃) and / or (a₂₄) the monomer units of form oligomeric or polymeric homopolymers, copolymers or block or graft copolymers which are prepared separately and then mixed with polystyrene in such an amount, that the composition of the resulting portion (a₂) is within the critical limits given above. In this case, the carrier (a) building up mixture of PPE, polystyrene, at least one homo- or copolymer from the groups (a₂₁), (a₂₂), (a₂₃) and / or (a₂₄) and optionally other additives. The polystyrene generally has a weight average molecular weight<o ostyle="single">M</o>_w of over 8 · 10⁴, especially in the range of 1 · 10⁵ to 2 · 10⁵. It is of particular advantage to use the groups (a₂₂) and (a₂₃) together. These groups preferably form the monomer units of oligomeric α-methylstyrene-p-methylstyrene copolymers which can be prepared in a manner known per se by radical copolymerization in bulk or in solution and then added to the polystyrene in the amount required according to the invention. The copolymers of this type which are very particularly preferred according to the invention have a number average molecular weight <o ostyle="single">M</o>_n from 5 · 10³ to 1.5 · 10⁴. They generally have a weight average molecular weight<o ostyle="single">M</o>_w from 5 · 10³ to 3 · 10⁴., preferably from 6 · 10³ to 2.5 · 10⁴, and in particular from 7 · 10³ to 2 · 10⁴. In general, based on their respective amount, these copolymers consist of 1 to 99% by weight, in particular 2 to 98% by weight, of 1-methyl-1-phenylethylene groups (a₂₂) and 99 to 1% by weight, in particular 98 to 2% by weight of 4'-methylphenylethylene groups (a₂₃). These copolymers are added to the polystyrene in an amount of, based on (a₂), 1 to 30% by weight, preferably 4 to 23% by weight and in particular 4 to 5% by weight, with additional amounts of these copolymers also being added to the polystyrene in the range from about 7.5 to about 16% by weight, based on (a₂), have proven to be extremely cheap and advantageous. It should be ensured that the lower limit of 1% by weight, based on (a₂), which is relevant for the individual use of groups (a₂₂) and (a₂₃), is not undercut, which can easily be avoided by correspondingly selects composite copolymers. However, it has been shown that these lower limits, which are relevant for the individual use of groups (a₂₂) and (a₂₃), in the case of the above-described particularly preferred embodiment of the invention, according to which the proportion (a₂) of the carrier (a) builds up Mixture of a mixture of polystyrene and the low molecular weight α-methylstyrene-p-methylstyrene copolymers described above, which may contain additives, is not so critical, so that in this case there are also deviations, ie one of these lower limits for (a₂₂) or (a₂₃) can also be fallen below without having to accept serious disadvantages.

Furthermore, the proportion (a₂) of the carrier (a) constructing mixture of PPE and (a₂) may have additives compatible therewith, "compatible" being understood to mean the fact that these additives are distributed in the mixture without clouding and therein also in Do not become cloudy over time under the influence of laser light. These additives should therefore generally be molecularly dispersed in the mixture. In addition, they should absorb light of the wavelength λ in the range from 720 to 1000 nm only weakly or not at all. In general, these additives can be antioxidants, lubricants, plasticizers and dyes. Examples of suitable additives are tert-butyl cresol, white oil and zinc stearate. The additives can be added in an amount of up to 10% by weight, based on (a₂), care being taken that the polystyrene content or the content of phenylethylene groups (a₂₅) in (a₂) is not less than 40% .% sinks.

A very particularly preferred carrier (a) of the sheet-like, multilayer, laser-optical recording material according to the invention has concentric or spiral track grooves or other structures suitable for guiding the laser beams in one of its surfaces (a 1) and consists of a mixture of, based on the mixture, 34 to 40 wt.% PPE and 60 to 66% by weight of the share (a₂), the proportion (a₂) of this mixture, based on (a₂), out 68.7 to 96.889% by weight polystyrene of a weight average molecular weight <o ostyle="single">M</o>_w over 8 · 10⁴, 3 to 25% by weight of a statistical copolymer, based on its amount, 2 to 98% by weight of polymerized α-methylstyrene and 98 to 2% by weight of polymerized p-methylstyrene with a weight average molecular weight <o ostyle="single">M</o>_w from 7 · 10³ to 2 · 10⁴, 0.1 to 6% by weight of a plasticizer, for example white oil, 0.01 to 0.1% by weight of an antioxidant, for example tert-butyl cresol, and 0.001 to 0.2% by weight of a dye which absorbs light of the wavelength λ&gt; 720 nm only weakly or not at all, consists.

The further essential component of the sheet-like, multilayer, laser-optical recording material according to the invention is its amorphous, thermally changeable recording layer (b). These are the usual and known recording layers, as are usually used for laser-optical data recording according to the principles described at the beginning. In general, the recording layer (b) is 10 to 500 nm thick.

In addition, the recording materials according to the invention may contain further layers which may also be important for the function of the recording materials, such as customary and known reflection layers, anti-reflection layers or adhesive layers or layers which decompose on heating and form gases. In addition, the recording layers (b) can have optically clear protective layers on them, which prevent dirt particles or scratches from lying in the laser focus or that the layers (b) corrode. In general, customary and known polymers or silicon oxides are used for this. For this purpose, the recording material according to the invention can also be connected to an optically clear cover hood in a customary and known manner, such as by ultrasonic welding.

Two recording materials according to the invention can also be connected in pairs so that their recording layers face each other in parallel and there is a certain distance between them. This distance can be set in the usual and known manner with the aid of spacers, such as webs or small columns. However, a single recording material according to the invention can also have two recording layers on the opposite sides of a support (a).

The recording material according to the invention can be produced by customary methods known per se from the prior art. In general, these are based on the shaping processing of the mixture which forms the carrier (a) with the aid of injection molding technology. Usually and expediently, the structured surface (a 1) of the carrier (a) is formed in the desired shape during the injection molding of the carrier (a). After the injection molding of the carrier (a) (process step I), the respective recording layer (b), if appropriate after the application of intermediate layers, reflective layers, etc., on the or the structured surfaces (a 1) of the respective carrier (a) by vapor deposition, sputtering or applied by solution coating (process step II). After this, further layers can be applied to the respective recording layer (b), which are useful for the function of the recording material. The recording material can then be provided with a cover.

The carrier (a) building mixture of PPE and the portion to be used according to the invention (a₂) can be prepared per se with the help of any conventional and known mixing techniques. In the context of the present invention, however, it has proven to be particularly advantageous to produce the mixture by coextruding its constituents on a twin-screw degassing extruder. Here, the portion (a₂) of the mixture is melted on the extruder and the PPE is metered in continuously as a highly concentrated, preferably 10 to 80% solution in toluene or ethylbenzene into the melt. The components are homogeneously mixed with one another in the extruder at temperatures of 200 to 400 ° C., the solvent being distilled off continuously. However, the PPE can also be fed to the extruder in solid form, for example in the form of granules. The resulting mixture is discharged from the extruder under clean room conditions, granulated and fed to the injection molding machine. However, the mixture can also be fed directly into the injection molding machine.

The recording materials according to the invention can be written to using a writing laser beam with analog or digital data, it being known to use an analog modulated continuous wave laser for writing analog data and a pulse modulated laser to write digital data.

In general, suitable lasers have a beam power of 1 to 20 mW at the write wavelength λ. The focus diameter of the writing laser beam is generally 300 to 2000 nm. In general, the pulse duration when irradiated with a pulse-modulated laser is 10 to 1000 ns. It is advantageously used for registered mail. a laser beam of light of wavelength λ, which is well absorbed by the relevant recording layer (b). Wavelengths λ of 400 to 1000 nm are advantageous.

During the writing process, the laser beam is guided over the recording material in relative motion and strikes it vertically or at an angle. When striking vertically, it must be focused on recording layer (b) when striking obliquely. At the point of impact, the recording layer (b) is heated locally and thermally changed areas arise, for example in the form of holes, craters, spots, relief structures or magnetized areas. When writing data with pulse-modulated laser beams, these areas essentially have a round or oval base with a diameter of 100 to 2000 nm, when writing with an analog modulated continuous wave laser, they can have any shaped base.

The recording materials according to the invention are outstandingly suitable for all known types of laser-optical data recording. They are particularly suitable for magneto-optical data recording.

The data can be written into the recording layer (b) from the side of the layer facing away from the carrier (a) or through the optically clear carrier (a). The latter is particularly advantageous.

The written data is read using a reading laser beam. The beam power of the reading laser at the reading wavelength λ 'is below the threshold power from which writing is possible. In general, the beam power is 0.1 to 2 mW. It is advantageous to use laser light of wavelength λ ', which is strongly reflected by the recording layer. Wavelengths λ 'of 400 to 1000 nm, in particular 630 to 900 nm, are advantageous.

During the reading process too, the reading laser beam is guided over the recording material in relative movement and strikes it perpendicularly or obliquely. When striking vertically, it must be focused on recording layer (b) when striking obliquely.

If the reading laser beam strikes a thermally changed area when the recording layer (b) is scanned, the properties of the light transmitted or reflected by the recording material change, which can be detected with the aid of suitable detectors.

The data in the recording layer (b) can be read from the side of the layer (b) facing away from the carrier (a) or through the carrier (a), the latter being advantageous. It is particularly advantageous here to detect the reflected light.

In addition, it is particularly advantageous to use write and read lasers for this purpose, which emit laser radiation in the infrared wavelength range from 630 to 900 nm. It is also advantageous if the write wavelength λ is identical to the read wavelength λ 'or differs only slightly from it. Light of these wavelengths is supplied by conventional and known semiconductor lasers.

The recording materials according to the invention are thus written through the carrier (a) in a procedure preferred according to the invention with pulse-modulated laser light of wavelength λ from 630 to 900, in particular 740 to 850 nm.

Thereafter, the recording materials described are read out in a preferred manner according to the invention with laser light of wavelength λ 'from 630 to 900, in particular 740 to 850 nm, from the side of the support (a), the light reflected from the recording layer (b) being detected.

If the recording materials according to the invention are in the form of data disks, the customary and known disk drives can be used for writing and reading digital data.

The recording materials according to the invention have numerous particular advantages.

They can be produced in a simple manner, and their property profile can be reproduced particularly easily and reliably.

Because of the particular advantageous properties of the mixture which forms the carrier (a), the carrier (a) can be injection molded under conditions which are particularly gentle on the material. This results in a very excellent impression of the track grooves, which have a consistently good shape profile over the entire surface of the carrier (a). The carriers (a) have no thermal deformation and a significantly reduced internal stress after their production. In addition, the proportion of PPE in the mixture can be reduced below that known from the prior art without the carrier (a) produced therefrom showing birefringence. The reduction of the comparatively difficult to process PPE portion in the mixture leads not only to a cost reduction but also to an even gentler and more precise injection molding process. The corresponding carriers (a) then still have excellent heat resistance and dimensional stability, a high modulus of elasticity and high hardness, and extremely low water absorption. In addition, they absorb light of a wavelength λ of over 600 nm to a very small extent or not at all, so that they are particularly suitable for the generally preferred writing and reading of the data through the carrier (a). In addition, the carriers (a) are also outstandingly suitable for the production of audio or video compact discs. In addition to the aforementioned laser-optical recording materials with an amorphous, thermally changeable recording layer (b), the invention accordingly also relates to audio or video compact discs which have a carrier (a) according to the invention of the type described above. In the compact disks, the data information is not written into a recording layer by means of laser beams in the form of thermally changed areas, but is transferred to the disk in a known manner by the mastering process, that is to say stamped into the carrier (a) of the disk.

The "tracking" behavior of the recording materials according to the invention is excellent, ie the tracking servo and autofocusing devices of the customary and known disk drives function very precisely in the recording materials according to the invention. The tracking servo and autofocusing devices respond even better to the recording materials according to the invention than to recording materials which only contain known carriers.

Overall, the recording materials according to the invention have an increased service life, can be written with comparatively low laser power and have a signal-to-noise ratio of over 45 dB. Because of their particularly high bit density and their extremely low bit error rate, the recording materials are ideal for recording video signals. They are also suitable as archive data disks.

Examples and comparative tests

In the following examples and comparative experiments, the thickness of the individual layers was determined on scanning electron microscope images.

The signal-to-noise ratio was determined in a known manner on recording materials which had been written through the carrier (a) using a pulse-modulated laser (wavelength λ of the emitted light: 830 nm; pulse duration 500 ns; light output: 6 mW). For this purpose, the recording materials were read with the aid of a continuous wave laser (wavelength λ of the emitted light: 780 nm; light output: 0.5 mW) through the support (a). The emitted reading laser beam was always guided over the recording layers at a relative speed of 4 m / s. The light reflected from the recording materials was always detected and analyzed.

In the following examples and comparative tests, supports (a) were used which contained concentric ruts on their surface. The track grooves serve for the exact guidance of the write and read laser beams, which are emitted by the laser-optical read and write head of the disk drive. For this it is necessary that the tracking servo devices in the laser-optical head receive sharp optical signals. These signals are produced by diffraction of the laser light reflected from the recording material to the laser-optical head at the boundary between "groove" and "land", the photodiode arrangements customary and known for this purpose being used for the detection and analysis of these light signals. For the "tracking" behavior, ie the exact guidance, in particular of the reading laser beams, it is essential that there is a high optical contrast between "land" and "groove", because otherwise only weak and broadened signals or no signals at all are obtained. The latter is often the case with the recording materials described. However, this leads to a low signal-to-noise ratio and makes it difficult to find written data again. The width of the signals and the difference in the intensity of the laser light reflected by a “groove” and a “land” are therefore generally used as a measure of the quality of the “tracking”. An additional quality criterion is whether this difference in intensity is constant and high over the entire diameter of the recording material.

Accordingly, the "tracking" behavior of the recording materials was determined in the following by reading the materials with a reading laser beam (λ = 780 nm; light output: 0.5 mW) across the track grooves. The measurement was carried out over the entire diameter of the recording material. The reflected laser light was detected with the aid of conventional optical arrangements, photodiodes were fed in and converted into electrical signals by suitable electronic components, the height of which was recorded as a function of the diameter. It was judged whether the differences between the height of the signals obtained from the lands and that from the grooves obtained were consistently sharp and high over the entire diameter of the recording material, and the following rating of the " tracking "behavior: "very good" sharp signals; high difference between the heights of the "land" and "groove" signals, which is constant over the entire diameter; "good" sharp signals; small difference between the relevant signal levels, which varies more or less across the entire diameter; "unsatisfactory" broad, washed-out signals; little difference between the relevant signal levels; this difference may also vary more or less across the entire diameter; "bad" no longer a difference between the signal levels concerned.

In order to check whether the writing on the recording materials resulted in a change in their "tracking" behavior, both the blank and the writing materials described were measured and graded in the manner explained above. If there were serious differences in the "tracking" quality of a recording material in the unwritten state on the one hand and in the described state on the other hand, this was a serious disadvantage. If this difference in quality, starting from a high level, was small, this demonstrated the particular advantage of the recording material in question.

The melt flow index (MFI) of the mixtures produced, the reflectivity (%) and the writing sensitivity (nJ) of the recording layers (b) and the birefringence of the supports (a) were determined using customary and known measuring methods.

Examples 1 to 2 and Comparative Experiment 1

Production and properties of carrier (a) to be used according to the invention (Examples 1 and 2) and a known carrier (comparative test 1);

Mixtures were produced under exactly comparable conditions in which the poly (2,6-dimethylphenylene ether) fraction (PPE) was not sufficient, according to the teaching of US Pat. No. 4,373,065, to fully compensate for the orientation birefringence of the mixtures. The mixtures had the following composition:

Comparative experiment 1

32.5 kg of radically polymerized polystyrene with a weight average molecular weight <o ostyle="single">M</o>_w from 1.65 · 10⁵ and 17.5 kg poly (2,6-dimethylphenylene ether) (PPE);

example 1

30.0 kg of polystyrene as in comparative experiment 1, 2.5 kg of a copolymer of α-methylstyrene (10% by weight) and p-methylstyrene (90% by weight) with a weight average molecular weight <o ostyle="single">M</o>_w of 9 · 10³ and 17.5 kg PPE as in comparative experiment 1;

Example 2

27.5 kg of polystyrene as in comparative experiment 1, 5.0 kg of a copolymer as in Example 1 and 17.5 kg PPE as in comparative experiment 1.

The proportion (a₂) of the mixtures (comparative experiment 1: polystyrene; examples 1 and 2: polystyrene plus copolymer) was melted on a twin-screw degassing extruder, and the PPE was metered into the respective melt as a 60% solution in toluene.

The mixtures were homogenized on the twin-screw extruder with degassing at 280 ° C. and a residence time of one minute, discharged from the extruder under clean room conditions and processed into granules.

The granules, which had been predried at 110 ° C., were made into disks under clean room conditions on a 90-ton injection molding machine and a special tool for optical storage disks [carrier (a), examples 1 and 2; known carrier, comparative experiment 1] sprayed. Concentric ruts were stamped on one side of the carrier using a nickel die inserted into the tool. The beams were 1.2 mm thick and 130 mm in diameter; the embossed track grooves were 70 nm deep and 0.6 µm wide ("groove") with a distance of 1.6 µm ("land").

The injection molding parameters were set for each of the three mixtures, with the main focus being on planarity of the carriers and minimal birefringence between crossed polarizing filters. The results can be found in Table 1.<tables id="tabl0001" num="0001"><table frame="all"><title>Table 1</title><tgroup cols="5" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="31.50mm" /><colspec colnum="2" colname="col2" colwidth="31.50mm" /><colspec colnum="3" colname="col3" colwidth="31.50mm" /><colspec colnum="4" colname="col4" colwidth="31.50mm" /><colspec colnum="5" colname="col5" colwidth="31.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col5" align="center">Injection molding parameters of the mixtures and property profile of the carriers made from them</entry></row><row rowsep="1"><entry namest="col1" nameend="col2" align="left">Injection molding parameters and property profile of the carrier</entry><entry namest="col3" nameend="col3" align="center">See vers. 1</entry><entry namest="col4" nameend="col4" align="center">example 1</entry><entry namest="col5" nameend="col5" align="center">Example 2</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Melt flow index MFI according to DIN 53 735 of the mixtures at 300 ° C and a contact force of 5 kp</entry><entry namest="col2" nameend="col2" align="left">(g / 10 min)</entry><entry namest="col3" nameend="col3" align="right">66</entry><entry namest="col4" nameend="col4" align="right">81</entry><entry namest="col5" nameend="col5" align="right">97</entry></row><row><entry namest="col1" nameend="col1" align="left">Injection speed of the mixtures</entry><entry namest="col2" nameend="col2" align="left">(mm / sec)</entry><entry namest="col3" nameend="col3" align="right">90</entry><entry namest="col4" nameend="col4" align="right">100</entry><entry namest="col5" nameend="col5" align="right">120</entry></row><row><entry namest="col1" nameend="col1" align="left">optimal injection temperature for the mixtures</entry><entry namest="col2" nameend="col2" align="left">(° C)</entry><entry namest="col3" nameend="col3" align="right">350</entry><entry namest="col4" nameend="col4" align="right">340</entry><entry namest="col5" nameend="col5" align="right">330</entry></row><row><entry namest="col1" nameend="col1" align="left">Color of the straps</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="left">yellow</entry><entry namest="col4" nameend="col4" align="left">yellow</entry><entry namest="col5" nameend="col5" align="left">light yellow</entry></row><row><entry namest="col1" nameend="col1" align="left">Maximum birefringence of the discs in the radius range 25 to 60 mm</entry><entry namest="col2" nameend="col2" align="left">(nm)</entry><entry namest="col3" nameend="col3" align="right">15</entry><entry namest="col4" nameend="col4" align="right">2</entry><entry namest="col5" nameend="col5" align="right">2</entry></row><row><entry namest="col1" nameend="col1" align="left">Track groove impression on the carriers</entry><entry namest="col3" nameend="col3" align="left">Well</entry><entry namest="col4" nameend="col4" align="left">very good</entry><entry namest="col5" nameend="col5" align="left">very good</entry></row><row><entry namest="col1" nameend="col1" align="left">Flatness of the porters</entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" align="left">Well</entry><entry namest="col4" nameend="col4" align="left">very good</entry><entry namest="col5" nameend="col5" align="left">very good</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Maximum continuous use temperature of the carrier</entry><entry namest="col2" nameend="col2" align="left">(° C)</entry><entry namest="col3" nameend="col3" align="right">125</entry><entry namest="col4" nameend="col4" align="right">125</entry><entry namest="col5" nameend="col5" align="right">125</entry></row></tbody></tgroup></table></tables>

As the comparison shows, the carriers (a) of examples 1 and 2 according to the invention have many improvements over those of comparative test 1: the lowering of the melt viscosity led to a lowering of the injection temperature and to reduced thermal damage to the mixtures. Furthermore, the impression in the tool was significantly improved without the maximum continuous use temperature being reduced. Particularly noteworthy is the drastic reduction in the orientation birefringence to almost no longer measurable values. Accordingly, the supports (a) according to the invention (Examples 1 and 2) are clearly superior to the known supports (comparative test 1).

Examples 3 to 4 and Comparative Experiment 2

Production and properties of recording materials according to the invention (Examples 3 and 4) and a known recording material (Comparative Experiment 2);

At 3000 revolutions per minute, two of the supports (a) from Examples 1 and 2 (for Examples 3 and 4) and two known supports from Comparative Experiment 1 (for Comparative Experiment 2) were propelled with a propanolic solution (4 % By weight) of a mixture of a dye absorbing at λ = 700 to 850 nm and a solution polymer of methyl methacrylate and methacrylic acid. The weight ratio of dye / polymer was 70:30. A trichinocyclopropane dye was used as the dye. After drying, recording materials with recording layers (b) approximately 100 nm thick were obtained, the reflectivity of which was determined to be 19% for light of the wavelength λ = 780 nm (measurement in a known manner through the supports).

In each case two identical recording materials were glued sandwich-like with the dye layers on the inside, a spacer ring of 300 μm thickness being interposed as a spacer.

Digital data was written into the grooves of the recording materials on a disk drive. Then the data was read.

The results obtained are shown in Table 2. <tables id="tabl0002" num="0002"><table frame="all"><title>Table 2</title><tgroup cols="4" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col4" align="center">Laser-optical data recording with recording materials according to the invention and not according to the invention</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">parameter</entry><entry namest="col2" nameend="col2" align="center">Comparative experiment 2^a)</entry><entry namest="col3" nameend="col3" align="center">Example 3^b)</entry><entry namest="col4" nameend="col4" align="center">Example 4^c)</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Writing sensitivity</entry><entry namest="col2" nameend="col2" align="left">1-2 nJ</entry><entry namest="col3" nameend="col3" align="left">1-2 nJ</entry><entry namest="col4" nameend="col4" align="left">1-2 nJ</entry></row><row><entry namest="col1" nameend="col1" align="left">Read signal</entry><entry namest="col2" nameend="col2" align="left">Well</entry><entry namest="col3" nameend="col3" align="left">Well</entry><entry namest="col4" nameend="col4" align="left">Well</entry></row><row><entry namest="col1" nameend="col1" align="left">"Tracking" behavior of the blank recording material</entry><entry namest="col2" nameend="col2" align="left">Well</entry><entry namest="col3" nameend="col3" align="left">very good</entry><entry namest="col4" nameend="col4" align="left">very good</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">"Tracking" behavior of the recording material described</entry><entry namest="col2" nameend="col2" align="left">unsatisfactory</entry><entry namest="col3" nameend="col3" align="left">Well</entry><entry namest="col4" nameend="col4" align="left">Well</entry></row></tbody></tgroup><tgroup cols="4" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><tbody valign="top"><row><entry namest="col1" nameend="col4" align="justify">^a) Carrier from comparative experiment 1</entry></row><row><entry namest="col1" nameend="col4" align="justify">^b) Carrier (a) from Example 1</entry></row><row><entry namest="col1" nameend="col4" align="justify">^c) Carrier (a) from Example 2</entry></row></tbody></tgroup></table></tables>

The results can be summarized as follows:

While the application properties caused by the dye layer, such as writing sensitivity and reading signal, were not influenced by the different carriers, a clear improvement in tracking was observed in the recording materials according to the invention (Examples 3 and 4): The very narrowly described parts of the known recording material could hardly be read, but the tracking of the recording materials according to the invention was easy to observe.

Example 5

Production and properties of a recording material according to the invention having a tellurium recording layer (b);

On a support (a) produced according to Example 1, tellurium was evaporated on one side in a vacuum apparatus in a layer thickness of 50 nm.

Digital data was written into the "grooves" on a disk drive and then read out. The signal / noise ratio was 52 dB.

Example 6

Production and properties of a magneto-optical recording material according to the invention;

A 90 nm thick AlN layer was sputtered onto a plurality of supports (a) produced in accordance with Example 1 in a high vacuum apparatus. A mixture of the composition 2 parts by weight of Nd, 18 parts by weight of Dy, 95 parts by weight of Tb and 30 parts by weight of Co was then applied in vacuo in a layer thickness of 75 nm. To protect the magneto-optical recording layer, a 50 nm thick SiO was applied to it_x-Evaporated layer. Digital data was written into the recording layer on a disk drive and read magneto-optically. The signal / noise ratio was always 50 dB.

Comparative experiment 3

Production and properties of a magneto-optical recording material with a known carrier;

Example 6 was repeated with the difference that instead of the supports (a) to be used according to the invention, supports from comparative experiment 1 were used.

The recording materials thus obtained had a signal / noise ratio of less than 45 dB.

Example 7

Production and properties of an audio compact disc with a carrier (a) to be used according to the invention;

Audio compact discs were produced from the mixture described in Example 1. For this purpose, the granulate was pre-dried and sprayed with the same injection molding machine but a different tool with a compact disk die. The supports (a) obtained had a diameter of 100 mm and were free from birefringence.

The light yellow supports (a) were vacuum-coated with a thin aluminum layer and coated with a protective lacquer. The compact disks were played in a commercially available device; no differences in the playback quality compared to the usual polycarbonate plates could be found.