Elements Having Layers Containing Mixtures Which Can Be Crosslinked by Photopolymerization

Preparation of a mixture which can be crosslinked by photopolymerization, and of photocrosslinked films of the said mixture.

246.80 g of polymer I-1 according to Table 1, 18.70 g of hexane-1,6-diol diacrylate, 9.20 g of hexane-1,6-diol dimethacrylate, 3.35 g of benzil dimethyl acetal and 1.39 g of 2,6-di-tert-butyl-p-cresol were dissolved in 370 g of toluene at 65.degree. C. Some of the solution was applied, by knife coating, onto a 125 .mu.m thick polyester sheet coated with a 2 .mu.m thick nylon film (nylon copolymer of dimeric alkane dicarboxylic acids having a molecular weight of 565 and hexamethylenediamine), the thickness of the cast layer being adjusted with the aid of a knife coater so that, after the toluene had been evaporated off at 80.degree. C., a photocrosslinkable film about 0.7 mm thick remained. This film was covered with a transparent 25 .mu.m thick polyethylene sheet and exposed uniformly for 15 minutes from the front and back using a flat-plate exposure unit equipped with 40 watt UV tubes. The temporary base and cover sheet were removed to give a self-supporting photocrosslinked film which had a tensile strength of 11.1 N/mm.sup.2 and an elongation at break of 264%, 4.6 N/mm.sup.2 being required for 100% elongation. The increase in weight due to swelling after 24 hours at 25.degree. C. was 0.9% in ethanol, 0.1% in water and 13% in ethanol/ethyl acetate (weight ratio 7:3). Its recovery behavior was very good: the indentation produced by a cylindrical punch of 4 mm diameter by applying a load of 1000 g for 2 minutes decreases to 1.4% after relaxation for a further 2 minutes.

The original photocrosslinkable film showed only a very small tendency to creep under load.

Another part of the casting solution was poured into frames so that, after the toluene had been evaporated off and drying had been carried out at 25.degree. C. for 7 days, at 80.degree. C. for 3 hours and at 50.degree. C. for 24 hours, 6 mm thick photocrosslinkable films were obtained. These were covered on each side with a transparent film and exposed uniformly for 15 minutes on both sides. The resulting photocrosslinked films had a Shore A hardness of 55 and a resilience of 67%.

Preparation of mixtures which are crosslinkable by photopolymerization, and of photocrosslinked films of the mixtures.

In Examples 2 to 6, the formulation stated in Example 1 was used, except that, instead of the polymer I-1 according to Table 1, other polymers I were used. The preparation of the mixtures, the films and the sheets, and the test procedure, were carried out as described in Example 1. Table 3 gives an overview of the test results. For the sake of clarity, the test results from Example 1 are also included.

Preparation of a mixture which can be crosslinked by photopolymerization, and of photocrosslinked films of this mixture.

A casting solution was prepared from 156.60 g of polymer I-3 according to Table 1, 13.40 g of hexane-1,6-diol diacrylate, 6.60 g of hexane-1,6-diol dimethacrylate, 2.40 g of benzil dimethyl acetal, 1.00 g of 2,6-di-tert-butyl-p-cresol, 12 mg of Sudan deep black (C.I. 26,150), 10.00 g of liquid paraffin (medicinal white oil, aromatics-free, viscosity (25.degree. C.)=140 mPa.s, pour point =-9.degree. C., density (15.degree. C.)=0.865 g/cm.sup.3), 10.00 g of a p-methylstyrene-.alpha.-methylstyrene copolymer (softening point =95.degree.-110.degree. C., refractive index (25.degree. C.)=1.58, melt viscosity (130.degree. C.)=1 Pas) and 200 g of toluene, and a 5.7 mm thick photocrosslinked sheet was prepared from this casting solution as described in Example 1, in a casting frame. The said photocrosslinked sheet had a Shore A hardness of 55 and a resilience of 62 %. Furthermore, the mixture was converted to a 0.7 mm thick sheet according to Example 1, and the residual deformation of this sheet was measured as described in Example 1. It was found to be 1.4%.

Preparation of a mixture which can be crosslinked by photopolymerization, and of photocrosslinked films of this mixture.

A mixture was prepared by extruding 25.00 kg of granulated polymer I-4 according to Table 1, 1.50 kg of liquid paraffin according to Example 7, 1.01 kg of hexane-1,6-diol diacrylate, 0.49 kg of hexane-1,6-diol dimethacrylate, 1.50 kg of p-methylstyrene/ .alpha.-methylstyrene copolymer according to Example 7, 0.36 kg of benzil dimethyl acetal, 0.15 kg of 2,6-di-tert-butyl-p-cresol and 1.8 kg of Sudan deep black (C.I. 26,150) in a twin-screw extruder. To do this, the liquid components (liquid paraffin and monomers) were mixed with the dye, the stabilizer and the photoinitiator, injected into the mixing extruder and mixed at 136.degree. C. with the thermoplastic components, and the resulting mixture was extruded at 150.degree. C. via a slot die. With the aid of calender, the extruded mixture was applied with one side on a 125 .mu.m thick polyethylene terephthalate film covered with a 5 .mu.m thick phenoxy resin/polycarbonate adhesion-promoting layer, and was covered on the other side with a nylon-coated polyethylene terephthalate film according to Example 1, and the multilayer element was brought to a total thickness of 3.01 mm.

Some of the extruded mixture was discharged without calendering and used to produce 0.7 mm and 5.7 mm thick sheets according to Example 1. The thick sheet had a Shore A hardness of 55 and a resilience of 62%, while the thin sheet had a residual deformation of 1.4% after the punch indentation test according to Example 1.

Preparation of a mixture which can be crosslinked by photopolymerization, and of photocrosslinked films of this mixture.

The procedure described in Example 8 was followed, except that polymer I-7 was used instead of polymer I-4. The photocrosslinkable film had an extremely small tendency to creep.

A 5.7 mm thick photocrosslinked sheet prepared from the mixture as described in Example 1 had a Shore A hardness of 59 and a resilience of 61%.

Preparation of a mixture which can be crosslinked by photopolymerization, and of photocrosslinked films of this mixture.

A mixture as described in Example 8, in which polymer I-8 was used instead of polymer I-4, was converted to a casting solution in toluene as described in Example 1 and processed in a similar manner to give 5 mm thick photocrosslinked sheets.

The Shore A hardness of the 5 mm thick sheet was 74 and its resilience was 59%. According to the punch indentation test described in Example 1, the residual deformation was 0.5%.

Preparation of a liquid mixture which can be crosslinked by photopolymerization, and its use as a coating film.

156.00 g of polymer I-6 according to Table 1, 30.00 g of hexane-1,6-diol dimethacrylate, 1.00 g of 2,6-di-tert-butyl-p-cresol and 2.40 g of benzil dimethyl acetal were mixed with one another at 60.degree. C. to give a homogenous mixture. Samples were taken and cast on glass, metal and plastic sheets. The resulting coating films were covered with polyethylene sheets and exposed uniformly for 30 minutes through the cover sheets. After the latter had been peeled off, transparent coating films having a Shore A hardness of 25 were obtained.

Preparation of a mixture which can be crosslinked by photopolymerization, and its use as a photocurable adhesive.

100 g of polymer I-4 according to Table 1, 80 g of a piperylene/2-methylbut-2-ene copolymer (Wingtack 95.sup.R from Goodyear), 20 g of 1,1,1-trimethylolpropane trimethacrylate, 1.5 g of 2,6-di-tert-butyl-p-cresol and 3 g of benzil dimethyl acetal were dissolved in 160 g of cyclohexane at 60.degree. C. A sample of this solution was used to coat a polyethylene terephthalate film, and the solvent was evaporated at 50.degree. C. The resulting dry, photocurable adhesive layer was laminated with a further polyethylene terephthalate film and exposed uniformly for 2 minutes. The adhesion of the photocured adhesive to the two films was excellent, and they could no longer be separated from one another without damaging the entire laminate.

Preparation of mixtures which can be crosslinked by photopolymerization, and the ozone stability of the photocrosslinked films prepared from these.

Webs of 2.84 mm thick multilayer elements were extruded and calendered as described in Example 8, except that nylon-coated polyethylene terephthalate bases as described in Example 1 were used instead of the polyethylene terephthalate bases provided with an adhesion-promoting layer. In Example 14, polymer I-10 according to Table 1 was used instead of polymer I-4.

Samples were removed from the film webs and exposed uniformly on both sides for 15 minutes in each case. After the cover sheets and temporary bases had been peeled off, the mechanical properties were determined; a summary is given in Table 4.

The stability to ozone was tested as follows: 2 cm wide test strips of the webs were each exposed on one side for 10 minutes, treated with a mixture of tetrachloroethylene and n-butanol (volume ratio=4:1) for 6 minutes, dried at 80.degree. C. for 1 hour, stored at room temperature for 15 hours, after-treated with a 0.4% strength aqueous bromine solution for 5 minutes and postexposed for 10 minutes. The resulting pieces of film could accordingly be regarded as models for flexographic printing forms.

The pieces of film were exposed at 24.degree. C. to air having an ozone content of 50 pphm, in an ozone chamber. In the case of the pieces of film according to Example 13, the first ozone cracks were observed after 150 minutes; in the case of those according to Example 14, the said cracks were observed after 30 minutes. Accordingly, only pieces of film according to Example 13 exhibited satisfactory ozone stability in the absence of antiozonants.

Preparation of a mixture which can be crosslinked by photopolymerization, and of printing forms based on this mixture.

A 0.7 mm thick relief-forming layer RL was produced on a nylon-coated polyethylene terephthalate film from a mixture according to Example 1, which additionally contained 2.4 mg of Sudan deep black (C.I. 26,150), the said layer RL being produced as described in Example 1. The free surface of RL in this multilayer element was laminated, with the aid of a laminating roll, with a 125 .mu.m thick polyester film coated with a phenoxy resin/polycarbonate adhesion-promoting layer. The mixture of adhesive-forming components contained, as an antihalation agent, a mixture of a yellow auramine dye (auramine FA, Basic Yellow 2, C.I. 41,000) and 4,4'-bis-(N-.beta.-hydroxyethyl-N-methylamino)-benzophenone in a weight ratio of 4:1, having an extinction of 0.40 at a wavelength .lambda. of 360 nm. After the lamination procedure, the original base was peeled off, the nylon layer remaining on RL. A photographic test negative was placed on the nylon-coated side of RL, and RL was exposed imagewise for 10 minutes with the aid of a flat-plate exposure unit. Thereafter, the exposed multilayer element was developed in a brush washer with a mixture of 3 parts by volume of tetrachloroethylene and 1 part by volume of n-butanol, after-treated with a 0.4% strength bromine solution for 3 minutes, dried, and postexposed uniformly for 10 minutes. A flexographic printing form which had a well defined relief having crisp edges and good shadow well depths in the continuous tone areas was obtained. Excellent print results were obtained when printing was carried out on a flexographic printing press using an ethanol-based ink. The printing form showed no abrasion, cracks or deformation, even after several hours' printing.

Preparation of a mixture which can be crosslinked by photopolymerization, and of printing plates based on this mixture.

A multilayer element consisting of a 125 .mu.m thick polyethylene terephthalate sheet, a 2 .mu.m thick nylon intermediate layer and a 0.7 mm thick relief-forming layer RL was produced, as described in Example 1, with the aid of the casting solution according to Example 7, and was kept for further use.

A 75 .mu.m thick polyethylene terephthalate sheet was coated on both sides with a 5 .mu.m thick phenoxy resin/polycarbonate adhesion-promoting layer and kept for further use. The adhesion-promoting layer which subsequently faces RL contained an antihalation agent according to Example 15.

To produce a base according to German Laid-Open Application DOS 2,444,118, 196.00 g of polymer I-9 according to Table 1, 75.00 g of a liquid polybutadiene having a molecular weight of 1300, a viscosity (25.degree. C.) of 7 Pas and a density of 0.89 g/cm.sup.3 and containing about 40% by weight of 1,2 structural units, 3.60 g of benzil dimethyl acetal, 24.00 g of hexane-1,6-diol dimethacrylate and 1.50 g of 2,6-di-tert-butyl-p-cresol were dissolved in 250 g of toluene, and the solution was cast, as described in Example 1, on a nylon-coated polyethylene terephthalate sheet in such a way that a 1.00 mm thick photocrosslinkable film remained after drying. (A sample of this multilayer element was exposed uniformly; the photocrosslinked film had a Shore A hardness of 39 and a resilience of 60%). The polyethylene terephthalate sheet coated with an adhesion-promoting layer was laminated with the free surface of this film in a calender, the adhesion-promoting layer which did not contain any antihalation agent being bonded to the film. The resulting multilayer element was exposed uniformly on both sides for 15 minutes using 40 watt UV tubes, after which the free adhesion-promoting layer of the exposed multilayer element was bonded, by lamination, to the free surface of RL in the initially produced multilayer element.

This multilayer element was exposed uniformly for 12 minutes through the base. Thereafter, the upper polyethylene terephthalate sheet was peeled off from RL and the latter was exposed imagewise through a photographic test negative placed on top and was developed, these tests being carried out as described in Example 15. Print tests with this printing form on a flexographic printing press gave a print run of more than 100,000 coupled with very good image reproduction.

Preparation of a mixture which can be crosslinked by photopolymerization and of printing forms based on this mixture.

The 3.01 mm thick multilayer element produced as described in Example 8 was cut to size to give flexographic printing plates of commercial size (0.6.times.0.32 m). A flexographic printing plate of this type was pre-exposed uniformly for 1 minute through the base, after which the cover sheet was peeled off, the nylon layer remaining on RL. RL was exposed for 14 minutes through a photographic test negative placed on the nylon layer, and was developed as described in Example 15 in a brush washer, and the resulting flexographic printing form was dried for 1 hour at 80.degree. C. and stored at room temperature for 15 hours. The printing form was then brominated for 3 minutes in a conventional manner, dried again and postexposed uniformly for 10 minutes.

The flexographic printing form produced in this manner, or its relief layer, possessed a relief depth of 800 .mu.m and had a very good side wall structure and very crisp edges. Print tests with this printing form on a flexographic printing press gave print results showing very exact image reproduction.