Process for the production of photostructured layers with improved mechanical properties

p0001The present invention is a process for producing photo-structured layers and three-dimensional objects, in which one or more layers of a photosensitive mixture of a both photopolymerizable and also thermally curable Plastisoldispersion imagewise exposed and the unexposed regions are removed and then the photopolymerized areas are thermally postcured ,

p0002For the production of structured layers methods are now widely used in which light-sensitive layers to imagewise exposure and then the exposed or the unexposed regions are removed, eg by washing. can be thermally cured (eg EP-B 00 particularly in the production of printing plates, etching or plating resists and solder masks, so-called negative-working mixtures are used which polymerize or crosslink (eg DE-C 22 15 090) and possibly under the influence of light. 73 444 and EP-B 00 63 304).

p0003This type of photo-structuring takes place also in the production of three-dimensional objects increasingly use. Various methods, form the three-dimensional models the gradual establishment of many individual photo-hardened layers are known (US 4,575,330; EP-A 02 50 121; US ​​4,752,498 and J. Imaging Technol, 15 (4), 186-190 (1989) and the. references cited therein). These processes are both techniques that work with different exposure masks for each layer, as well as those who write directly with a laser the desired structure into the polymerizable layers used. The recent publications but do not deal with special light-sensitive mixtures for three-dimensional objects, but only with the process technology, the well-known for other products photosensitive materials. These usually consist of a polymeric binder, a liquid photopolymerizable monomer and a photoinitiator, wherein additives such as fillers, inhibitors of thermal polymerization, dyes, etc. may also be included. but prepared with these mixtures materials often have insufficient mechanical strength. The processing of such polymerizable mixtures is difficult because their viscosity is very high. To reduce the viscosity usually plasticizers. These have the disadvantage that they easily exude from the finished material.

p0004A special kind of polymer / plasticizer mixtures are plastisols or organosols. These are 40 - 80 wt% dispersions of polymers in liquid, non-volatile plasticizers, which are capable of dissolving the polymers in heating the dispersion above a certain temperature (gelling or Plastisoltemperatur).. Upon cooling to room temperature this phase arise solid, transparent materials. Also volatile solvents can these dispersions are added. If their content is less than 10 wt.% Is known as plastisols, with higher solvent content of organosols.

p0005Plastisols, which monomers and photoinitiators or thermal initiators are added and thus, subsequent to the thermal polymer plasticizer-fusion can be cured / are known. Such reactive plastisols are as described in the patents US 2,618,621; DE-A 30 06 349; US 4,523,983 or US 4,623,558 described. Mixtures of a plastisol, a polyfunctional monomer and / or an epoxy resin, a photoinitiator and a thermal initiator that can be used as sealants and adhesives are described in J. Radiat. Curing, 10 (4), 8-11 (1983) and DE-A 33 14 896 described. This plastisol be solidified by a short fixed by flood exposure (as described in US 4,634,562 for blends without thermal initiator), and then be fully cured by thermal treatment. The thermal polymerization is here used to cure the adhesive, where photopolymerization is not possible. In the method of plate making according to US 4,176,028 plastisols are used which are only photocurable and their thermal fusion is utilized to form a photopolymerizable layer. This is then laminated to the substrate and then exposed and washed out image-wise by the usual method. Here, of course, no plastisols may be used include thermal initiators and thus in the formation of the photopolymerizable layers form very hard layers, otherwise removing the unexposed areas will be affected.

p0006Another process for the production of printing plates that uses the combination of plastisol and photopolymerizable mixture, is described in US 3,615,448 and WJ Nebe in Symposium photopolymer system Washington 1978, Adv. Printing of Summaries, S. 75-56. In this case, a layer consisting of a plastisol, a photosensitive compound such as a monomer, a crosslinkable polymer or a polymerizable plasticizer, and a photoinitiator, imagewise exposed and then heated. Thereby fuse the unexposed areas and form on cooling, solid, non-tacky areas. The exposed parts can then be washed out or toned. Plastisolverschmelzung and photocuring occur in this process in various areas, whereby imagewise differentiated between the thermally fusible and non-fusible areas by photopolymerization of the monomers, polymers or plasticizers.

p0007The object of the present invention is to provide a method, structured layers or three-dimensional objects can be prepared with which, starting from a photosensitive composition having a high mechanical resistance. They should have high tensile strength, high shore hardness, low extensibility, high rigidity and low shrinkage as a result of the curing process. In addition, no plasticizer migration should take place and the photosensitive compositions should be easy to process and easy to handle. At the same time it should be ensured an exact reproduction of the displayed images or models. This object is achieved by a process for producing photo-structured layers comprising<ul><li>a) forming a layer of a photosensitive mixture comprising<ul><li>1. a thermally fusible polymer / plasticizer dispersion,</li><li>2. at least one addition-polymerizable ethylenically unsaturated compound,</li><li>3. a photoinitiator or a photoinitiator system and</li><li>4. a thermally reactive compound,</li></ul></li><li>b) imagewise exposing the photosensitive layer prepared according to a),</li><li>c) removing the unexposed areas, and</li><li>d) thermal post.</li></ul>

p0008The production of three-dimensional objects is performed by a method according to claim 2nd

p0009With the present method it is possible to bring the benefits of reactive plastisols for imagewise Photostructuring usable. None of the known method for processing of reactive plastisols suggests the inventive method. It is surprising that adverse effects may occur either in the image-wise exposure and removal of the unexposed areas even during the thermal fusion or thermal curing. It was not to be expected, above all, in spite of previous photopolymerization the thermal fusion is still possible, although it is known from the prior art that contain just by imagewise exposure of plastisols, the monomers and photoinitiators between thermally fusible and non-fusible areas can be differentiated.

p0010Essential to the invention is the use of a photosensitive composition which is both photopolymerizable as well as thermally fusible and curable. As the binder system of the photosensitive mixture of the invention, a polymer / plasticizer dispersion is used which fuses when heated to a phase which hardens on cooling to a solid, transparent mass. At the same time due to the due to the use of a plastisol high plasticizer content of a low viscosity and therefore a good processability of the photosensitive composition. The combination of a monomer or a monomer with a photoinitiator and a thermally reactive compound requires the possibility of image-wise photopolymerization and subsequent thermal post-cure. Surprisingly, the stability and handling of the photosensitive mixture was not significantly affected by the addition of a thermally reactive compound, although conventional photosensitive mixtures inhibitors must be added to the thermal polymerization. It was also surprising that the strength of the structured materials was highest with short exposure times

p0011An essential point of the method of the invention is that the thermal treatment takes place after the removal of the unexposed areas.

p0012The thermal treatment thus extends only to the exposed areas, whose mechanical properties can be substantially improved. The stabilization of the patterned by imagewise photopolymerization materials is indeed caused in part by the Plastisolverschmelzung of the binder system, however, a further gain only takes place by an additional thermal curing. Structured Materials, who found out by a thermal treatment this twofold gain, have sufficient mechanical strength and resistance to heavy loads and also have a high service life. A structured material which was only cured by the Plastisolverschmelzung, has lower tensile strength, higher elongation and plasticizer migration.

p0013For essential to the invention thermal curing the photosensitive composition preferably contains a thermal initiator and a additionspolymersierbare ethylenically unsaturated compound. This may be the monomer used for photopolymerization or a monomer mixture, which was not fully implemented in the photopolymerization. This can be achieved by short exposure times, limiting the photoinitiation by choosing a high optical density, preferably D ≧ 1.3, or incorporation of less reactive monomers. Monomer mixtures are preferably used which contain monomers of different reactivity. The more reactive monomer is photopolymerized in the imagewise exposure for patterning of the material, and the monomer having the lower reactivity is thermally polymerized while the post-treatment to strengthen the material. In addition, the monomers of the polymers must be compatible. In particular, the less reactive monomer must be compatible especially at elevated temperature with the polymer. On the other hand, the monomers may not swell the polymer at room temperature. Suitable monomers of different reactivity are for example acrylates and methacrylates. The following monomers are for example suitable: ethyl acrylate and methacrylate, 1,4-butanediol diacrylate and methacrylate, isodecyl acrylate and methacrylate, Dicyclopentenyldiacrylat and methacrylate, 2-ethylhexyl acrylate and methacrylate, lauryl acrylate and methacrylate. Particularly advantageous are trimethylolpropane triacrylate and methacrylate, or 1,6-hexanediol acrylate and methacrylate or ethoxylated trimethylolpropane triacrylate, and N-vinylpyrrolidone. Thermal polymerization may not take place below the Plastisoltemperatur, but at, but preferably above, this temperature. That is, the thermal polymerization is to take place within the thus formed phase only after Plastisolverschmelzung. This is achieved in that a thermal initiator is used, at, or preferably above the Plastisoltemperatur disintegrates. Suitable thermal initiators are, for example t-butyl hydroperoxide, t-butyl perbenzoate, cumene hydroperoxide.

p0014A further embodiment of the invention, thermal curing by means of connections which are thermally cross-linkable with itself and / or with one or more other components of the mixture. For this purpose ÜR suitable, for example compounds with epoxy, hydroxyl, alkyl ether, acyl and hydroxyalkyl. Particularly suitable are compounds having at least two epoxy groups, and melamine derivatives. Preference is given to hexamethoxy melamine, 3,4-Epoxycyclohexylcarbonsäure-3,4-epoxycyclohexanecarboxylate, and 2,2-bis (glycidoxy-phenyl) -propane used.

p0015As photopolymerization initiators known per se photoinitiators or initiator systems are also suitable, such as benzoin, benzoin, α-methylbenzoin or its ethers, benzil dimethyl and systems such as benzophenone / Michler's ketone and thioxanthone / amine. According to the invention the polymer / plasticizer dispersion, that merge with increasing temperature is used as the binder system. Suitable plastisols and organosols having 40 to 80 are wt.%, Preferably 50 to 70 wt.%, Of a homo- or copolymer of vinyl chloride, vinyl acetate, vinyl propionate, vinyl stearate, vinyl ethers, vinylpyridine, styrene, acrylic acid and methacrylic acid or their esters such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, octyl (meth) acrylate, (meth) acrylonitrile, etc. mixtures of more of said homopolymers or copolymers or polymers of the core / shell type can be used. The molecular weight of the polymers should 10000-200000, preferably 50000-180000, lie. Particularly suitable are polymers having a molecular weight from 70,000 to 150,000.

p0016Plasticizers that 20 to 60 wt.%, Preferably 30 to 50 wt.% Make the plastisol, for example, phosphates, phthalates, sebacic or adipic acid esters are suitable. Particularly suitable are dibutyl phthalate, diisodecyl phthalate, butyl benzyl phthalate, tricresyl phosphate, tributyl phosphate, in particular phthalate and Triethylenglyoldiacetat. And thermally polymerizable plasticizers such as diallyl phthalate, triallyl phosphate and may be used.

p0017The photosensitive compositions according to the invention usually contain from 40 to 90 wt.% Of the binder system, 5 to 30 wt.% Of monomer, 0.01 to 5 wt.% Of photoinitiator and 0.1 to 5, preferably 0.5 to 2 wt.% Of thermal initiator or preferably 1 to 30, 10 to 20, wt.% of a thermally cross-linkable with itself and / or with one or more other components of the mixture compound.

p0018Furthermore, customary additives such as thickeners such as SiO₂, Fillers, dyes, stabilizers as in the photosensitive mixture. Especially advantageous is the addition of compounds which when heated to the Plastisoltemperatur water, CO_2, N₂, Etc. release such as potassium bicarbonate. Hereby the occurring in the curing shrinkage usually be reduced. The present process for the production of structured layers comprises forming a layer of the inventively essential light-sensitive mixture, if necessary. On a support, image-wise exposing this layer, removing the unexposed regions and the thermal after-treatment. Suitable support materials include glass, metallic carriers, metal-clad carrier and plastic films such as polyester.

p0019The application of the photosensitive composition on the support material can be carried out by the conventional coating methods such as casting, dipping, spraying, etc.. The layer thickness is usually 2-750 .mu.m, preferably 25 to 400 microns. The need for image-wise exposure to actinic radiation can UV, visible or IR light be, preferably UV light is used. The exposure is carried out eg with mercury vapor lamps, xenon lamps or carbon arc lamps. Particularly advantageous is the use of lasers. Not photopolymerized areas may be removed by an air stream, or by treatment with liquid or vaporous solvents. If necessary this may be washed with a suitable solvent such as trichloroethane. Removing the non-photopolymerized areas can also be made directly by washing with the usual development solvent. Subsequently, the thermal post-curing is carried out in an electric furnace or by means of an IR lamp. The temperature should be 80 to 200 ° C, are preferably from 100 to 180 ° C. The duration of the heat treatment depends on the used photosensitive composition and is between 15 and 60 minutes.

p0020Essential to the invention, photosensitive compositions are preferably used for producing three-dimensional objects. They are particularly suitable for the layered structure of these objects, with the individual layers of light-sensitive mixtures are applied over one another and individually exposed imagewise. For this purpose, the use of laser beams for the direct writing of the photosensitive layers is particularly advantageous as it is described for example in US 4,575,330 or EP-A 02 50 121st The formation of the individual layers of the photosensitive composition can be made in which the light-sensitive mixture is gradually added to prepare the respective layer by various conventional methods. but it is also possible to give the entire light-sensitive mixture in a container which contains a vertically movable support plate. At the beginning of the process is this support plate on the surface of the photosensitive mixture and coated with a layer of this mixture covered. This layer is exposed imagewise. Subsequently, the carrier plate is lowered, thus resulting in a new, light-sensitive layer. The newly-formed photosensitive layer is then exposed image-wise also. These process steps are repeated until the three dimensional object is fully assembled. Treatment continues as the single method.

example 1

p0021A dispersion of 10 g of polyvinyl chloride (MW 110000), 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 in a layer thickness of 0 , 3 mm is applied on a copper plate and with a controlled by a raster scanner argon laser (360 nm, 250 mJ / cm²) A circuit pattern exposed accordingly. The unexposed areas were rinsed with a mixture of ethanol and trichloroethane: away (1: 1). Subsequently, the thus patterned layer was heated for 5 min at 180 ° C. This gave an exact reproduction of the circuit template.

example 2

p0022Dispersion A and Dispersion B (such as A but without dibenzoyl peroxide) were dissolved in a layer thickness of 0.3 mm with an argon laser (360 nm, 250 mJ / cm²) The entire surface exposed and then heated for 5 min at 180 ° C. The tensile strength F and the extension L were measured with a Zwick instrument 1435th<tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="3" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="52.50mm" /><colspec colnum="2" colname="col2" colwidth="52.50mm" /><colspec colnum="3" colname="col3" colwidth="52.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="center">F [N / mm²]</entry><entry namest="col3" nameend="col3" align="center">L [%]</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">dispersion A</entry><entry namest="col2" nameend="col2" align="right">43</entry><entry namest="col3" nameend="col3" align="right">6</entry></row><row><entry namest="col1" nameend="col1" align="left">dispersion B</entry><entry namest="col2" nameend="col2" align="right">31</entry><entry namest="col3" nameend="col3" align="right">10</entry></row></tbody></tgroup></table></tables>

example 3

p0023Two samples of the dispersion A were exposed to light in a layer thickness of 0.3 mm with an argon laser (360 nm). The exposure energy was:<ul><li>a) 50 mJ / cm²</li><li>b) 500 mJ / cm²</li></ul> Then the layers were heated for 3 min at 180 ° C. The tensile strength of the samples was determined as in Example 2:<ul><li>a) 49 N / mm²</li><li>b) 40 N / mm²</li></ul> The experiment shows that in order to increase the strength of a diffusible residual amount of monomer before the thermal treatment must be present.

example 4

p0024A dispersion of 10 g of powdered polymethylmethacrylate (MW 150 000), 4 g of ethoxylated trimethylolpropane triacrylate, 5.5 g 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 on a copper plate in a thickness of 0.4 mm and having a controlled through a raster scanner argon laser (360 nm, 60 mJ / cm²) A circuit pattern exposed accordingly. The unexposed areas were washed with a mixture of 1,1,1-trichloroethane and ethanol. Then 5 min was heated to 140 ° C. This gave an exact reproduction of the circuit template.

example 5

p0025For the preparation of a cubic object of the edge length 1.5 cm, the dispersion of Example 4 was placed in a container, in which there was a vertically movable support plate. At the beginning of the process of this support 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 about 360 nm corresponding to a square. The diameter of the laser beam was 150 microns. was controlled laser over a raster scanner. The exposure energy per unit area was 90 mJ / cm², After exposure of the first layer, the carrier plate has been lowered so far that formed a new layer of the photosensitive dispersion. This layer was again exposed to the laser. These process steps were repeated until the cube-shaped object was fully assembled. A total of 50 layers were used. The layer thickness was 300 microns respectively. The photopolymerized object was removed from the container, the remaining, non-photopolymerized dispersion removed by an air stream and the cube-shaped object 10 min at 140 ° C heated. This gave a strong, flexible object that was an exact reproduction of the original.

example 6

p0026A 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 N-Ninylpyrrolidon (10 ppm N, N -di-sec-butyl-p-phenylenediamine), 3 g of benzil dimethyl ketal and 15 g of 3,4-epoxycyclohexylmethyl-3,4- epoxycyclohexanecarboxylate was applied in a layer thickness of 0.3 mm on a copper plate and with a controlled by a raster scanner argon laser (360 nm, 250 mJ / cm²) A circuit pattern exposed accordingly. The unexposed portions were removed with vaporous trichloroethane. Subsequently, the thus patterned layer was heated for 5 min at 150 ° C. This gave an exact reproduction of the circuit template.