Process for the production of photostructured layers with improved mechanical properties.

0001The present invention relates to a process for the production of photostructured layers and three-dimensional objects, in which one or more layers of a light-sensitive mixture of a plastisol dispersion which is both photopolymerizable and thermally curable are exposed imagewise and the unexposed areas are removed and then the photopolymerized areas are thermally post-cured .

0002Processes are frequently used today for producing structured layers in which light-sensitive layers are exposed imagewise and then the exposed or unexposed areas are removed, for example by washing out. So-called negative working mixtures are used in the production of printing plates, etching or galvanoresists and solder mask, which polymerize or crosslink under the influence of light (eg DE-C 22 15 090) and if necessary. can be cured thermally (e.g. EP-B 00 73 444 and EP-B 00 63 304).

0003This type of photo structuring is also increasingly used in the production of three-dimensional objects. Various methods are known which form three-dimensional models by gradually building up many individual photocured layers (US 4,575,330; EP-A 02 50 121; US ​​4,752,498 and J. Imaging Technol., 15 (4), 186-190 (1989) and the like literature cited therein). These processes use techniques that work with different exposure masks for each individual layer, as well as techniques that write the desired structure directly into the polymerizable layers with a laser. However, the previous publications have not dealt with special light-sensitive mixtures for three-dimensional objects, but only with process engineering, using the light-sensitive materials known for other products. These usually consist of a polymeric binder, a liquid, photopolymerizable monomer and a photoinitiator, additives such as fillers, inhibitors against thermal polymerization, dyes, etc. can also be included. However, materials made with these mixtures often have insufficient mechanical strength. The processing of such polymerizable mixtures is also difficult since their viscosity is very high. Plasticizers are usually added to lower the viscosity. However, these have the disadvantage that they sweat out easily from the finished materials.

0004A special type of polymer / plasticizer mixtures are plastisols or organosols. These are 40-80% by weight dispersions of polymers in liquid, non-volatile plasticizers, which are able to dissolve the polymers when the dispersion is heated above a certain temperature (gelling or plastisol temperature). When this phase cools down to room temperature, solid, transparent materials are created. Volatile solvents can also be added to these dispersions. If their content is below 10% by weight, one speaks of plastisols, with a higher solvent content of organosols.

0005Plastisols to which monomers and photoinitiators or thermal initiators are added and which can thus be post-cured after the thermal polymer / plasticizer fusion are known. Such reactive plastisols are described, for example, in US Pat. Nos. 2,618,621; DE-A 30 06 349; US 4,523,983 or US 4,623,558. Mixtures of a plastisol, a polyfunctional monomer and / or an epoxy resin, a photoinitiator and a thermal initiator, which can be used as sealing compounds and adhesives, are described in J. Radiat. Curing, 10 (4), 8-11 (1983) and DE-A 33 14 896. These plastisol mixtures are solidified by being fixed by a brief full exposure (as is also described in US Pat. No. 4,634,562 for mixtures without a thermal initiator) and then completely hardened by thermal treatment. Thermal polymerization is used here to harden the adhesive where photopolymerization is not possible. In the process for the production of printing plates according to US Pat. No. 4,176,028, plastisols are used which are only photocurable and whose thermal fusion is used to form a photopolymerizable layer. This is then laminated onto the carrier material and then imagewise exposed and washed out by the usual method. Of course, no plastisols may be used here which contain thermal initiators and thus form very hard layers when the photopolymerizable layers are formed, since otherwise the removal of the unexposed areas is impaired.

0006Another method of making printing plates using the combination of plastisol and photopolymerizable mixture is described in US 3,615,448 and WJ Nebe in Symposium Photopolymer Systems Washington 1978, Adv. Printing of Summaries, pp. 75-56. Here, a layer consisting of a plastisol, a light-sensitive compound such as a monomer, a crosslinkable polymer or a polymerizable plasticizer and a photoinitiator is exposed imagewise and then heated. The unexposed areas merge and form solid, non-sticky areas when cooling. The exposed parts can then be washed out or toned. Plastisol fusion and photocuring occur in this area in different areas, with the image being differentiated between the thermally fusible and non-fusible areas by the photopolymerization of the monomers, polymers or plasticizers.

0007The object of the present invention is to provide a method with which, starting from a light-sensitive mixture, structured layers or three-dimensional objects can be produced which have high mechanical resistance. They should have high tensile strength, high shore hardness, low ductility, high rigidity and low shrinkage as a result of the hardening process. In addition, there should be no plasticizer migration and the light-sensitive mixtures should be easy to handle and easy to process. At the same time, an exact reproduction of the images or models to be displayed should be guaranteed. This object is achieved by a method for producing photostructured layers comprising<ul id="ul0001" list-style="none"><li>a) forming a layer comprising a photosensitive mixture<ul id="ul0002" list-style="none"><li>1. a thermally fusible polymer / plasticizer dispersion,</li><li>2nd at least one addition-polymerizable, ethylenically unsaturated compound,</li><li>3rd a photoinitiator or a photoinitiator system and</li><li>4th a thermally reactive connection,</li></ul></li><li>b) imagewise exposure of the light-sensitive layer produced according to a),</li><li>c) removing the unexposed areas and</li><li>d) thermal aftertreatment.</li></ul>

0008Three-dimensional objects are produced by a method according to claim 2.

0009With the present method, it is possible to utilize the advantages of reactive plastisols for image-like photostructuring. None of the known methods for processing reactive plastisols suggests the method according to the invention. It is surprising that neither image-wise exposure and the removal of the unexposed areas, nor thermal fusion or thermal curing, have any adverse effects. Above all, it was not to be expected that, despite previous photopolymerization, thermal fusion would still be possible, although it is known from the prior art that it is precisely through imagewise exposure of plastisols which contain monomers and photoinitiators that there is between thermally fusible and non-fusible regions can be differentiated.

0010Essential to the invention is the use of a light-sensitive mixture which is both photopolymerizable and thermally fusible and curable. A polymer / plasticizer dispersion is used as the binder system of the light-sensitive mixture according to the invention, which melts when heated to a phase which hardens to a solid, transparent mass on cooling. At the same time, the high proportion of plasticizer due to the use of a plastisol results in a low viscosity and therefore good processability of the light-sensitive mixture. The combination of a monomer or a monomer mixture with a photoinitiator and a thermally reactive compound results in the possibility of imagewise photopolymerization and the subsequent thermal post-curing. Surprisingly, the stability and handling of the light-sensitive mixture was not significantly impaired by the addition of a thermally reactive compound, although inhibitors against thermal polymerization have to be added to conventional light-sensitive mixtures. It was also surprising that the strength of the structured materials was highest with short exposure times

0011An essential point of the method according to the invention is that the thermal treatment is carried out only after the unexposed areas have been removed.

0012The thermal treatment therefore only extends to the exposed areas, the mechanical properties of which can be significantly improved as a result. The stabilization of the materials structured by imagewise photopolymerization is effected in part by the plastisol fusion of the binder system, but further reinforcement takes place only through additional thermal curing. Structured materials that have undergone this double reinforcement through thermal treatment have sufficient mechanical strength and resistance to heavy loads and also have a long service life. A structured material that has only been hardened by the plastisol fusion exhibits lower tensile strength, higher elongation and plasticizer migration.

0013For the thermal curing essential to the invention, the light-sensitive mixture preferably contains a thermal initiator and an addition-polymerizable, ethylenically unsaturated compound. This can be the monomer used for the photopolymerization or a monomer mixture which was not completely implemented in the photopolymerization step. This can be achieved by short exposure times, limitation of photoinitiation by choosing a high optical density, preferably D ≧ 1.3, or admixing less reactive monomers. Monomer mixtures which contain monomers of different reactivity are preferably used. The more reactive monomer is photopolymerized during imagewise exposure to structure the material, and the monomer with the lower reactivity is thermally polymerized during post-treatment to reinforce the material. In addition, the monomers must be compatible with the polymers. Above all, the less reactive monomer must be compatible with the polymer, especially at elevated temperatures. On the other hand, the monomers must not swell the polymer at room temperature. Suitable monomers with different reactivity are, for example, acrylates and methacrylates. The following monomers are suitable, for example: ethyl acrylate and methacrylate, 1,4-butanediol diacrylate and methacrylate, isodecyl acrylate and methacrylate, dicyclopentenyl diacrylate and methacrylate, 2-ethylhexyl acrylate and methacrylate, lauryl acrylate and methacrylate. Trimethylolpropane triacrylate and methacrylate or 1,6-hexanediol acrylate and methacrylate or ethoxylated trimethylolpropane triacrylate and N-vinyl pyrrolidone. The thermal polymerization must not take place below the plastisol temperature, but at, but preferably above, this temperature. This means that the thermal polymerization should only take place after the plastisol fusion within the phase formed thereby. This is achieved by using a thermal initiator that decomposes at, or preferably above, the plastisol temperature. Suitable thermal initiators are, for example, t-butyl hydroperoxide, t-butyl perbenzoate, cumene hydroperoxide.

0014A further embodiment of the invention comprises thermal curing by means of compounds which can be thermally crosslinked with themselves and / or with one or more other components of the mixture. For example, compounds with epoxy, hydroxy, alkyl ether, acyl and hydroxyalkyl groups are suitable for this. Compounds with at least two epoxy groups and melamine derivatives are particularly suitable. Hexamethoxy-melamine, 3,4-epoxycyclohexylcarboxylic acid-3,4-epoxycyclohexylmethyl ester and 2,2-bis (glycidoxyphenyl) propane are preferably used.

0015Suitable photo polymerization initiators are the photoinitiators or initiator systems known per se, such as, for example, benzoin, benzoin alkyl ether, α-methylbenzoin or its ether, benzil dimethyl ketal and systems such as, for example, benzophenone / Michler's ketone and thioxanthone / amines. According to the invention, polymer / plasticizer dispersions which fuse when the temperature rises are used as the binder system. Plastisols and organosols with 40 to 80% by weight, preferably 50 to 70% by weight, of a homo- or copolymer of vinyl chloride, vinyl acetate, vinyl propionate, vinyl stearate, vinyl ether, vinyl pyridine, styrene, acrylic acid and methacrylic acid or their esters such as, for example, are suitable Methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, octyl (meth) acrylate, (meth) acrylonitrile, etc. Mixtures of several of the homo- or copolymers or polymers of the core / shell type mentioned can also be used be used. The molecular weight of the polymers should be between 10,000 and 200,000, preferably between 50,000 and 180,000. Polymers with a molecular weight between 70,000 and 150,000 are particularly suitable.

0016Suitable plasticizers, which make up 20 to 60% by weight, preferably 30 to 50% by weight, of the plastisol dispersions are, for example, phosphates, phthalates, sebacic acid or adipic acid esters. Dibutyl phthalate, diisodecyl phthalate, butyl benzyl phthalate, tricresyl phosphate, tributyl phosphate, in particular diethyl hexyl phthalate and triethylene glycol diacetate, are particularly suitable. Thermally polymerizable plasticizers such as triallyl phosphate and diallyl phthalate can also be used.

0017The light-sensitive mixtures according to the invention usually contain 40 to 90% by weight of the binder system, 5 to 30% by weight of monomer, 0.01 to 5% by weight of photoinitiator and 0.1 to 5, preferably 0.5 to 2% by weight of one thermal initiator or 1 to 30, preferably 10 to 20,% by weight of a compound which can be thermally crosslinked with itself and / or with one or more other components of the mixture.

0018Furthermore, conventional additives such as thickeners such as SiO₂, fillers, dyes, stabilizers can be contained in the light-sensitive mixture. Particularly advantageous is the addition of compounds that water, CO₂ when heated to the plastisol temperature_, Release N₂, etc. such as potassium hydrogen carbonate. As a result, the shrinkage that usually occurs during hardening can be reduced. The present method for producing structured layers comprises the formation of a layer of the light-sensitive mixture essential to the invention, possibly on a support, the imagewise exposure of this layer, the removal of the unexposed areas and the thermal aftertreatment. Suitable carrier materials are, for example Glass, metallic supports, metal-coated supports and plastic films such as polyester.

0019The light-sensitive mixture can be applied to the carrier material by the usual coating methods such as, for example, pouring, dipping, spraying, etc. The layer thickness is usually 2 to 750 microns, preferably 25 to 400 microns. The actinic radiation required for imagewise exposure can be UV, visible or IR light, UV light is preferably used. The exposure is carried out, for example, with mercury vapor lamps, xenon lamps or carbon arc lamps. The use of lasers is particularly advantageous. Non-photopolymerized areas can be removed by air flow or by treatment with liquid or vapor solvents. If necessary, it can be washed with a suitable solvent such as trichloroethane. The non-photopolymerized areas can also be removed directly by washing out with one of the customary development solvents. Then the thermal post-curing takes place in an electric furnace or by means of an IR lamp. The temperature should be 80 to 200 ° C, preferably 100 to 180 ° C. The duration of the thermal treatment depends on the light-sensitive mixture used and is between 15 and 60 minutes.

0020The light-sensitive mixtures essential to the invention are preferably used to produce three-dimensional objects. They are particularly suitable for the layer-by-layer construction of these objects, the individual layers of the light-sensitive mixtures being applied one on top of the other and individually exposed image-wise. For this purpose, the use of laser beams for direct writing to the light-sensitive layers, such as is advantageous, is particularly advantageous is described in US 4,575,330 or EP-A 02 50 121. The individual layers of the light-sensitive mixture can be formed by various customary methods in which the light-sensitive mixture is added step by step to produce the respective layer. However, it is also possible to put the entire photosensitive mixture into a container which contains a vertically movable carrier plate. At the beginning of the process, this carrier plate is located on the surface of the light-sensitive mixture and is covered with a layer of this mixture. This layer is exposed imagewise. The carrier plate is then lowered so that a new, light-sensitive layer results. The newly formed photosensitive layer is then exposed imagewise. These process steps are repeated until the three-dimensional object is completely built up. The further treatment is the same as for the single-layer process.

example 1

0021A dispersion A composed of 10 g of polyvinyl chloride (MW 110,000), 5 g of bis (2-ethylhexyl) phthalate, 3 g of trimethylolpropane triacrylate, 3 g of hexanediol diacrylate, 0.5 g of benzil dimethyl ketal and 0.2 g of dibenzoyl peroxide was applied in a layer thickness of 0 , 3 mm applied to a copper plate and exposed with an argon laser controlled by a raster scanner (360 nm, 250 mJ / cm²) according to a circuit pattern. The unexposed portions were removed by rinsing with a mixture of ethanol and trichloroethane (1: 1). The layer structured in this way was then heated to 180 ° C. for 5 minutes. An exact reproduction of the circuit template was thus obtained.

Example 2

0022Dispersion A and a dispersion B (like A only without dibenzoyl peroxide) were exposed to the full area in a layer thickness of 0.3 mm using an argon laser (360 nm, 250 mJ / cm²) and then heated to 180 ° C. for 5 minutes. The tensile strength F and the extension L were measured with a Zwick 1435 device.<tables id="tabl0001" num="0001"><img file="EP0442071A2_D0001.tif" /></tables>

Example 3

0023Two samples of dispersion A were exposed in a layer thickness of 0.3 mm with an argon laser (360 nm). The exposure energy was:<ul id="ul0003" list-style="none"><li>a) 50 mJ / cm²</li><li>b) 500 mJ / cm²</li></ul> The layers were then heated to 180 ° C. for 3 minutes. The tensile strength of the samples was determined as in Example 2:<ul id="ul0004" list-style="none"><li>a) 49 N / mm²</li><li>b) 40 N / mm²</li></ul> The experiment shows that to increase the strength, a diffusible residual amount of monomer must be present before the thermal treatment.

Example 4

0024A dispersion of 10 g of powdered polymethyl methacrylate (MW 150,000), 4 g of ethoxylated trimethylolpropane triacrylate, 5.5 g of dimethyl phthalate, 2 g of N-vinylpyrrolidone, 0.4 g of benzil dimethyl ketal and 0.2 g of 2,2-azo-bis-isobutyronitrile was applied to a copper plate in a layer thickness of 0.4 mm and exposed with an argon laser controlled by a raster scanner (360 nm, 60 mJ / cm²) according to a circuit pattern. The unexposed areas were washed out with a mixture of 1,1,1-trichloroethane and ethanol. The mixture was then heated to 140 ° C. for 5 minutes. An exact reproduction of the circuit template was obtained.

Example 5

0025To produce a cube-shaped object with an edge length of 1.5 cm, the dispersion of Example 4 was placed in a container in which there was a vertically movable carrier plate. At the beginning of the process, this carrier plate was in such a position that it was covered with a layer of the dispersion. This layer was exposed with an argon laser at approximately 360 nm corresponding to a square. The diameter of the laser beam was 150 µm. The laser was controlled via a raster scanner. The exposure energy per area was 90 mJ / cm². After the first layer had been exposed, the carrier plate was lowered until a new layer of the photosensitive dispersion was formed. This layer was exposed again with the laser. These process steps were repeated until the cube-shaped object was completely built up. A total of 50 layers were used. The layer thickness was 300 µm in each case. The photopolymerized object was removed from the container, the remaining, non-photopolymerized dispersion was removed by an air stream and the cube-shaped object was heated to 140 ° C. for 10 minutes. A solid, flexible object was obtained which was an exact reproduction of the template.

Example 6

0026A dispersion of 30 g of polyvinyl chloride (MW 110,000), 16 g of bis (2-ethylhexyl) phthalate, 9 g of 7,7,9-trimethyl-4,13-dioxo-3,14-dioxa-5,12-diaza -hexadecane-1,16-diol-dimethacrylate, 9 g of N-vinyl pyrrolidone (10 ppm of N, N -di-sec-butyl-p-phenylenediamine), 3 g of benzil dimethyl ketal and 15 g of 3,4-epoxycyclohexane carboxylic acid 3,4 epoxycyclohexylmethyl ester was applied in a layer thickness of 0.3 mm to a copper plate and with an argon laser controlled by a raster scanner (360 nm, 250 mJ / cm²) exposed according to a circuit pattern. The unexposed portions were removed with gaseous trichloroethane. The layer structured in this way was then heated to 150 ° C. for 5 minutes. An exact reproduction of the circuit template was thus obtained.