Moulding composition based on vinyl chloride polymers and process for preparing films from these moulding compositions for the preparation of securities protected against falsification

The invention relates to a molding composition based on vinyl chloride polymers for the production of films for the preparation of counterfeit-proof securities, the counterfeit security being that the securities produced can only be personalized by means of a laser. The invention further relates to a method for producing these films.

Securities, such as identity cards, credit cards and check cards, should be such that it is not or only very difficult to produce counterfeit or falsified items.

With regard to the structure, the known securities generally represent a composite of at least 2, preferably 3 layers (foils) made of the same or different plastics or of plastics and preferably paper or metal. As is well known, credit cards are currently in use, which are made up of 3 layers, the two outer layers (protective layers) consisting of a transparent or crystal-clear polyvinyl chloride film and the inner layer (the core) made of paper or a colored polyvinyl chloride film.

The currently used paper core credit card can be personalized with a laser, that is, it can be written on, and is therefore to a high degree of forgery-proof (due to the expensive and complicated technical equipment required for laser personalization), but it also has a number of disadvantages, such as low dimensional stability and thus a limited ability to machine, relatively high sensitivity to bending and breaking, short lifespan and relatively easy to delaminate. In addition, the font sharpness is rated as unsatisfactory.

The currently used credit cards aux plastic foils as core and as protective layers (all-plastic credit cards) obviously have several advantages compared to paper core credit cards, but they have the following considerable disadvantage: personalization (lettering) is done by embossing , which does not guarantee great security against counterfeiting. The security against forgery cannot be increased significantly by the known measures, such as the installation of magnetic strips or electrophotographic images.

The molding compositions for the production of the films which are used to prepare the credit cards described above consist essentially of vinyl chloride polymers as the main constituent, methyl methacrylate-butadiene-styrene polymers or acrylonitrile-butadiene-styrene polymers as modifiers to improve the impact resistance of vinyl chloride Polymers, conventional heat stabilizers and lubricants for vinyl chloride polymers and, if appropriate, dyes and fillers, like titanium dioxide and chalk. These molding compositions are relatively easy to calender and extrude. The calender films and extruder films obtained also have a surface quality which is satisfactory with regard to the production of securities. However, the all-plastic securities which are advantageous as such have, as already described above, a relatively low level of security against forgery.

In addition to a high level of security against counterfeiting, plastic films for the production of securities are also intended in particular to ensure a high processing speed (machine speed) in the production of the securities. In order to achieve a high processing speed, they must have a good surface finish, which is a surface that is particularly free of so-called cracks. The surface breaks in the film lead to malfunctions, for example when printing on the film and when pressing the film blanks to the desired bonds.

The object of the invention is therefore to provide a molding composition based on vinyl chloride polymers, which is characterized by good calendering and extrudability, preferably calendering, and provides films which are particularly advantageous for the production of securities because they are have the required surface finish and the securities produced can only be personalized using a laser.

The molding composition according to the invention based on vinyl chloride polymers consists of<ul id="ul0001" list-style="none"><li>A) 5 to 20% by weight of impact modifier for vinyl chloride polymers, selected from the group consisting of acrylonitrile-butadiene-styrene polymers, methyl methacrylate-butadiene-styrene polymers, methyl methacrylate-acrylonitrile-butadiene-styrene polymers and chlorinated polyethylene,</li><li>B) 0.5 to 25% by weight of pulverized pure cellulose which has an average degree of polymerization of 300 to 1,000 and whose particles have a maximum diameter of 0.09 mm,</li><li>C) 1 to 5 wt .-% polymethyl methacrylate, and</li><li>D) vinyl chloride homopolymers and / or vinyl chloride copolymers with at least 70% by weight of polymerized vinyl chloride units in such an amount that the total weight of A), B), C) and D) is 100% by weight, and in addition</li><li>E) an effective amount of lubricant and heat stabilizer for vinyl chloride polymers.</li></ul>

It was surprising that the molding composition according to the invention, despite the content of pulverized cellulose, can be easily extruded and also calendered, and provides films which in particular have the properties which are desired for the production of the most varied of types of securities. Molding compositions based on vinyl chloride polymers containing cellulose are known from German patent specification 25 14 691 and US Pat. Nos. 4,104,207 and 4,250,064. However, these molding compositions differ from those of the invention not only in terms of their qualitative and quantitative composition, but also in terms of the type of cellulose. The known molding compositions are also intended for completely different purposes compared to the new ones.

The impact modifiers for polyvinyl chloride (component A) to be used according to the invention are polymers of acrylonitrile, butadiene and styrene (ABS), methyl methacrylate, butadiene and styrene (MBS), methyl methacrylate, acrylonitrile, butadiene and styrene (MABS) and chlorinated polyethylene (CPE). The ABS, MBS and MABS polymers each have a butadiene content of preferably at least 35% by weight, based on the total polymer. ABS polymers whose content of butadiene is 40 to 70% by weight, styrene 20 to 40% by weight and acrylonitrile 10 to 25% by weight, based in each case on the total polymer, have proven particularly suitable; MBS polymers, the content of butadiene 40 to 70 wt .-%, of styrene 10 to 20 wt .-% and of methyl methacrylate 10 to 50 wt .-%. each based on the total polymer is; MABS polymers whose content of butadiene is 40 to 60% by weight, styrene 25 to 40% by weight, methyl methacrylate 15 to 30% by weight and acrylonitrile less than 10% by weight, based in each case on the total polymer , is.

The chlorinated polyethylene as an impact modifier for polyvinyl chloride is a chlorination product of polyethylene or of copolymers of ethylene with small proportions, preferably with at most 1 to 5 mol% of propene or butene- (1). The ethylene polymer, which is chlorinated, can have been produced in the low pressure or high pressure process. Chlorinated low pressure polyethylene is preferred. The average molecular weight of the chlorinated polyethylene is expediently 10,000 to 100,000, preferably 20,000 to 50,000 (calculated from the chlorine content and the molecular weight of the starting polyethylene determined by gel chromatography; cf. Journal "Makromolekulare Chemie", volume 26, year 1958, pages 96 to 101, publisher Dr. Alfred Hüthig, Heidelberg, Federal Republic of Germany). The chlorine content is advantageously 20 to 50% by weight, preferably 30 to 42% by weight, based on the chlorinated polyethylene.

The amount of impact modifier is preferably 10 to 15% by weight. based on the weight of the molding compound from components A), B), C) and D).

The cellulose to be used according to the invention (component B) is a pulverized, pure cellulose. which has an average degree of polymerization of 300 to 1000, preferably 400 to 950, and whose particles have a diameter of at most 0.09 mm, preferably 0.02 to 0.08 mm.

The word pure is intended to express that the cellulose to be used according to the invention essentially consists of D-glucopyranose molecules with β (1.4) -glucosidic linkage, that is to say that it is not a chemically modified or chemically refined cellulose such as alkyl cellulose, carboxyalkyl cellulose or rayon. The cellulose selected according to the invention is therefore a powdered cellulose of vegetable origin (in particular wood) freed from lignin and other accompanying substances, cleaned, chemically not modified or refined. Such celluloses are commercially available, for example under the name ARBOCEL^®-Cellulose (@ = registered trademark of J. Rettenmaier and Sons, filler factories in Holzmühle, Federal Republic of Germany). In the event that the films produced are to be crystal-clear or transparent, the amount of cellulose is 0.5 to 5% by weight, preferably 1 to 3% by weight, based on the weight of the molding composition from components A), B), C) and D). If, on the other hand, the films are to be covered with a matt coating, the amount of cellulose is 8 to 25% by weight. preferably 10 to 16 wt .-%, based on the weight of the molding composition from components A), B). C) and D).

The polymethyl methacrylate (component C) to be used according to the invention is a polymer of the ester from methacrylic acid and methanol (methyl methacrylate). The degree of polymerization of the polymethyl methacrylate can vary within wide limits. Preferred are polymethyl methacrylates with a relative viscosity of 1.2 to 20, preferably 4 to 10 (measured in a 1% by weight solution in chloroform using the Ubbelohde viscometer with the capillary Oa).

The amount of polymethyl methacrylate in the molding composition according to the invention is preferably 1.5 to 3% by weight, based on the weight of the molding composition composed of components A), B), C) and D).

The vinyl chloride polymers or polyvinyl chlorides (component D) to be used according to the invention can be homopolymers and / or copolymers of vinyl chloride. The proportion of polymerized vinyl chloride units in the copolymers is at least 70% by weight, preferably at least 85% by weight, based on the weight of the polymer.

The following monomers are particularly suitable for the copolymerization of vinyl chloride: olefins such as ethylene and propylene; Vinyl esters of carboxylic acids with 2 to 4 carbon atoms, such as vinyl acetate and vinyl propionate; Vinyl halides such as vinylidene chloride; unsaturated acids such as maleic, fumaric, acrylic methacrylic acid and their esters with alcohols with 1 to 10 carbon atoms; Acrylonitrile; Styrene; and cyclohexylmaleimide.

Particularly suitable for the graft polymerization of vinyl chloride are elastomeric polymers which are obtained by polymerizing one or more of the following monomers: dienes such as butadiene and cyclopentadiene; Olefins such as ethylene and propylene; Styrene; unsaturated acids such as acrylic and methacrylic acid and their esters with alcohols with 1 to 10 carbon atoms; and acrylonitrile.

Preferred vinyl chloride polymers are homopolymers of vinyl chloride and copolymers of vinyl chloride with vinyl acetate. These polymers are expediently prepared by the low-mass, low-suspension or low-emulsifier method (emulsifier less than 3% by weight, based on the polymer) of the emulsion polymerization process.

The K values ​​(DIN 53 726) of the vinyl chloride polymers are advantageously 50 to 80, preferably 54 to 67.

The amount of polyvinyl chloride, the main constituent of the molding compositions according to the invention, is preferably at least 68% by weight, based on the total weight of components A), B), C) and D), from which, taking into account the preferred amounts of component A) given , B) and C) for polyvinyl chloride the preferred amount range from 68 to 87.5 wt .-% results.

The usual organotin sulfur compounds, aminocrotonic acid esters, urea and thiourea derivatives and / or salts of the alkaline earth metals and zinc are preferably used as heat stabilizers for the molding compositions based on polyvinyl chloride (component E). The organotin sulfur stabilizers such as dimethyltin, dibutyltin and dioctyltin bis-2-ethylhexylthioglycolate are preferred. The effective amount of stabilizer is usually 0.5 to 3% by weight, preferably 1 to 2.0% by weight, based on the amount by weight of polyvinyl chloride (component D).

The following customary compounds are preferably used as lubricants (component E): stearic acid, montanic acid, glycerol esters such as glycerol monooleate, bis-palmitoyl-ethylenediamine, bis-stearoyl-ethylenediamine, montanic acid ester of ethanediol or 1,3-butanediol, optionally partially soaped. The effective amount of lubricant is usually 0.1 to 2.5% by weight. preferably 0.5 to 1.5% by weight, based on the amount by weight of polyvinyl chloride (component D).

The molding compositions according to the invention with a certain content of pulverized pure cellulose optionally contain further fillers, preferably titanium dioxide and chalk (calcium carbonate), in an amount of 1 to 15% by weight, preferably 3 to 10% by weight, based on the amount by weight Polyvinyl chloride (component D). The chalk can be treated (coated) or untreated chalk. The particles of the powdery fillers, chalk and titanium dioxide generally have a diameter of 0.001 to 0.015 mm, preferably 0.005 to 0.008 mm.

The molding compositions according to the invention are produced by mixing the individual components together, which is expediently carried out in a mixer customary in plastics processing.

The molding compositions according to the invention are processed into films by extrusion and preferably by calendering. The calendering is preferably carried out in such a way that the molding composition a) is pre-gelled at a temperature of 140 to 180 ° C., preferably 150 to 170 ° C., advantageously in a kneader and / or on a rolling mill consisting of at least two rollers, and b the calendered material is calendered to a film on a calender, preferably consisting of four or five rolls, at a roll temperature of 180 to 225 ° C., preferably 190 to 210 ° C. the rollers are heated in such a way that the first and the last roller have approximately the same temperature and the intermediate rollers have temperatures 5 to 10 ° C higher than the other two rollers (high-temperature calendering process). The calendered film is removed from the last calender roll, cooled with the aid of cooling rolls and usually fed to a winding device.

The thickness of the film is generally 0.1 to 1.0 mm, preferably 0.2 to 0.7 mm.

The molding compositions according to the invention are readily calenderable and extrudable. They can also be calendered at relatively high speed without difficulty. The calender foils have a good surface quality. Its surface is free from cracks and other imperfections (specks). These films are particularly suitable for the production of securities, for example credit cards. As already mentioned above, credit cards generally consist of a core film which is covered on both sides with a protective film (overlay film). The core film should be matt and easily printable. Preferred molding compositions according to the invention for the production of core films essentially consist of 5 to 20% by weight, preferably 10 to 15% by weight, of component A), 8 to 25% by weight, preferably 10 to 16% by weight , of component B), 1 to 5% by weight, preferably 1.5 to 3% by weight, of component C), vinyl chloride polymer as component D), lubricants and heat stabilizers as component E) and additionally fillers, selected from the group titanium dioxide and chalk in an amount of 1 to 15% by weight, preferably 3 to 10% by weight, as component F).

It is surprising that the filler combination of cellulose, chalk and / or titanium dioxide according to the invention gives a molding composition which can be easily calendered and provides films which are also particularly good with regard to mattness and printability. The protective film should be crystal clear or at least transparent. Preferred molding compositions according to the invention for producing such films essentially consist of 5 to 20% by weight, preferably 10 to 15% by weight of component A), 0.5 to 5% by weight, preferably 1 to 3% by weight. % of component B), 1 to 5% by weight, preferably 1.5 to 3% by weight of component C), vinyl chloride polymer as component D) and lubricant and heat stabilizer as component E).

The core foils and protective foils described can easily be put together to form bonds, because these foils are also easy to compress (pressing temperature 120 to 150 ° C.). The securities thus obtained, such as credit cards, are extremely forgery-proof because they can only be personalized using an expensive laser device (exposure to a laser causes the cellulose contained in the film to blacken as a result of combustion). As can be seen, the protective films of such a composite also contain cellulose proposed according to the invention. It has been found that pure cellulose also has a positive, additional influence on the laserability and thus on the typeface, if small amounts of it are also used in the protective film (overlay film).

The calender foils produced from the molding compositions according to the invention therefore have all those valuable properties which are desired for the preparation of securities, and the securities prepared are distinguished by a high level of security against forgery.

The invention will now be explained in more detail using examples:

Examples 1 to 8 and Comparative Examples 1 and 2

The examples and comparative examples are summarized in the table below.

The components mentioned were mixed in a high-speed mixer customary in plastics processing and the mixtures were pre-gelled in an extruder at temperatures of 150 to 170 ° C. The individual pre-gelled molding compounds were calendered on a calender with 4 rollers. The temperature of the calender rolls was 190 to 210 ° C depending on the molding compound. The thickness of the individual films was 0.2 mm in each case.

The calenderability of the molding compositions, the surface properties of the film and the typeface of laser-personalized credit cards that had been produced from the films were rated 1 to 3: 1 = unsatisfactory, 2 = good, 3 = very good.

The gloss of the two film surfaces according to ASTM D 523 and the tensile strength and the elongation at break according to DIN 53 455 were also measured in the longitudinal direction (1) and transverse direction (q) on the films. The results are in the table.

The credit cards (composites), on which the ability to be written on with a laser and the typeface were tested, were structured as follows:

The films from Examples 1, 2 and 5 each represented the outer layer (the protective films) when bonded to paper as the core layer.

The films from Examples 3, 4, 6, 7 and 8 each represented the core layer when combined with the film from Example 2 as the outer layer.

The film from Comparative Example 1 was the core layer when combined with the film from Comparative Example 2 as the outer layer.

The film from comparative example 2 represented the outer layer in the case of a composite with paper as the core layer.

The components specified in the table in brief form are described in more detail below:<ul id="ul0002" list-style="none"><li>PVC 'is a vinyl chloride homopolymer with a K value of 57,</li><li>PVC² is a vinyl chloride homopolymer with a K value of 60,</li><li>PVC³ is a copolymer with a K value of 60 made from 90% by weight vinyl chloride and 10% by weight vinyl acetate, PVC⁴ is a vinyl chloride homopolymer with a K value of 54,</li><li>CPE 'is a chlorinated polyethylene with a chlorine content of 39% by weight and an average molecular weight of 20,000,</li><li>CPE² is a chlorinated polyethylene with a chlorine content of 34% by weight and an average molecular weight of 45,000,</li><li>ABS is a polymer made from 24% by weight acrylonitrile, 48% by weight butadiene and 28% by weight styrene,</li><li>MABS is a polymer of 18% by weight methyl methacrylate, 3% by weight acrylonitrile, 42% by weight butadiene and 37% by weight styrene,</li><li>MBS is a polymer of 16% by weight methyl methacrylate, 66% by weight butadiene and 18% by weight styrene,</li><li>PMMA is a polymethyl methacrylate with a relative viscosity of 6.2 (Examples 1, 2, 5 and Comparative Examples 1 and 2) and 4.1 (other examples),</li><li>Cellulose: in example 8, pulverized pure cellulose with an average degree of polymerization of 950 and a maximum particle size of 0.08 mm was used, in the remaining examples one with an average degree of polymerization of 400 and a maximum particle size of 0.04 mm.</li></ul>(See table on page 6 f.)

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