GB2082593A - A plastics body modified in respect of optical properties - Google Patents

Abstract

The refractive index of a transparent, hard-elastic amorphous plastics body is increased by means of modifying agents. A solid modifying agent dissolved in a common solvent is incorporated into the polymer or monomer solutions from which the polymer is to be formed and the solvent is removed after working and/or synthesis of the plastics material. The polymer may be thermoplastic and/or formed from a plurality of polyadditionable components. The modifying agent may be thionalide, acridine, pyrene or N- phenylurea. For impressable layer bodies, the polymerisation plastics material has a give refractive index, softening point and melting point. For those, the solvent may be tetrahydrofuran, cyclohexane, methyl ethyl ketone or dimethylformamide; for multi- components plastics materials, it is a polyhydroxy alcohol. Machine-readable information carriers comprise a carrier, the impressable modified plastics layer and a protective layer. If transparent colouring agents and/or pigments are mixed with the high-refraction lacquer, paints or colours with a particularly high sheen are obtained.

Description

SPECIFICATION Methods of producing a plastics body modified in respect of optical properties This invention relates to methods of producing a plastics body modified in respect of optical properties.

In the description and claims, the term 'body' is used to denote true shaped or moulded bodies, but also layers and films.

It is known that many plastics materials can be worked more easily than inorganic materials. For many purposes however, the refractive index of the plastics materials, which is resricted by the nature of the plastics materials, is a disadvantage. Attempts have therefore been made to improve the property of plastics materials by means of additives. Thus, DE No. 2 218 782 A describes a method in which shaped members of transparent polymer for deflecting optical radiation are modified by means of low-molecular organic liquids by diffusion at temperatures below the glass transition point in such a way that there is formed in the polymer material a continous refractive index gradient, which extends virtually normal to the optical axis of the body.

It is known that plasticiser-like liquids dissolved in plastics materials tend to diffuse out and migrate into the environment, in particular into natural and synthetic polymers of the same and different kinds, which are in contact with them.

The invention results from efforts to solve the problem of providing a method of producing optically modified plastics materials in which the refractive index is not altered in respect of time and location and that have an increased refractive index extending in homogeneous mode throughout the entire body. In particular, the invention seeks to provide plastics layer tha can be imprinted or embossed and that can be adhesively applied to a carrier material, such as cardboard or plastics foil of the same or another material.

Finally, the invention also seeks to provide that films and foils can be cast on a provisional carrier and subsequently removed.

The invention provides a method of obtaining a modified plastics body having a higher refractive index than the corresponding unmodified body, the unmodified body being an amorphous, transparent, colourless, hardelastic polymer, comprising incorporating, in a solution of the polymer or of at least one of the solutions of the monomer(s) from which the polymer is to be formed, a solution in a common solvent of a colourless transparent non-crystallisation-causing modifying agent at a level of concentration that is insufficient to saturate the polymer, and removing the solvent after physical drying or after synthesis of the polymer.

The plastics bodies and layers produced in accordance with the invention may enjoy brightness and retain their transparency without further additives. They may also have excellent brilliance when mixed with colouring agents and pigments, as well as other desirable optical effects. Therefore, it is possible to produce surfaces with a better reflective action in shaped bodies, for example in the devices referred to as cats' eyes, in lenses with a smaller radius of curvature or other smaller dimensions and in lens combinations with a lower degree of achromatism and colouring layers of smaller thickness, thus enhancing economy and simplicity in use.

The Examples set out below, in which all parts are by weight, illustrate the invention and describe embodiments of it in greater detail. Examples 1 and 2 describe methods of producing shaped members with enhanced brightness and layers or coatings of improved strength, while Examples 3 to 6 describe methods of producing impressable or embossable layers for particular purposes.

References to 'parts' in the following examples mean 'parts by weight'.

Example 1 35 parts of an epoxy base resin with an epoxy equivalent of 500 is intimately mixed together with 30 parts of a hardener which comprises an aliphatic, aromatic or cycloaliphatic diamine.

95 parts of that mixture is homogeneously mixed, depending on the desired viscosity, with 30 parts of a solvent, preferably a glycol, and/or a higher alcohol, preferably ethylene glycol or a mixture of that glycol with butylene glycol, and 15 parts of finely divided thionalide which has been previously premixed and dissolved in a weighed amount of the above-indicated constituents at 70 to 80"C. Thionalide is aipha mercapto-N-2-naphthylacetamide with a molecular weight of 217.29 and a melting point of 109-111"C.

The unmodified epoxy resin comprising the above-mentioned constituents has a reactive index n20 of about 1.57.

Instead of thionalide, it is also possible for the modifying agent used to be another solid organic compound which is compatible with a polymer at a high level of concentration. These may be compounds with the photo-chemical transitions n ac* and z~z*, in particular those having the general formula:

N(C), (C)N = (C), (C) = S or (C) - Cl, wherein the symbols shown in brackets may be one or more components which are present in a chain or at least one ring and which are denoted by the appropriate symbol.

The mixture may be worked using known methods. Solidification and formation of the plastics body from the components is effected at room temperature or more rapidly at elevated temperature, while the solvent may also be a component. Films can also be cast on a temporary carrier and subsequently removed again therefrom.

The modifying agent is dissolved in the plastics body in solid form, and the latter remains completely transparent. Obviously, the concentration thereof should not reach the saturation point in the polymer.

Shaped or moulded bodies made from the modified epoxy resin have a refractive index nD of 1.61 to 1.64 when using aromatic diamines as the hardener; and a refractive index n20 of 1.59 to 1.61 when using aliphatic hardeners. These can be used for decorative items which have a strong refractive effect, with a subdivided reflective rear surface, for reflectors, or the like.

The optical efficiency of the modifying agent is dependent on the one hand on its concentration in the plastics body and on the other hand on its own refractive index. This in turn is a consequence of the chemical composition of the modifying agent. The proportion thereof is to be so selected that the mol refraction of the modifying agent with the mol refraction of the polymer additively give the desired refractive index or the plastics body.

If there are also added to the mixture of 95 parts of the epoxy resin component + 20 to 40 parts of methylene glycol + 15 parts of finely divided thionalide, a further 30 parts of titanium dioxide, in particular in the rutile form, and colouring pigments or transparent colouring substances and 2 parts of silica in submicroscopically finely divided form, and the whole is homogenised in a three-roll mill, it is possible to produce printing inks for copperplate printing or screen printing, which have an excellent covering capability and also brilliance and which have a pot time of about 10 hours. Because of their adhesion capability and their resistance to wear, such printing inks are particularly suitable for printing documents.

Example 2 Operation is as in Example 1, but the polymer-forming components, the modifying agent and the proportions used are different.

The components of the plastics material comprise 50 parts of a hydroxy-function acrylic resin and 10 parts of a low-viscosity polyisocyanate, the mixture being adjusted to equivalence in respect of the OH-groups of the acrylic resin and the isocyanate groups of the polyisocyanate. For this purpose, 10 parts of ethylene glycol and higher alcohols, depending on the desired viscosity, and from 10 to 15 parts of a mixture of 4:2 parts of pyrene and thionalide are added.

Pyrene:

General formula: C16H10 Molecular weight: 202.26 Melting point: 145 to 1480C The mixture has a pot time which is also about 10 hours and is so highly fluid that it can be used for lacquering or varnishing. While the solid unmodified lacquer has a refractive index nD of 1.538, the modified layer or coating of lacquer has a refrative index nD of 1.56 to 1.59 and therefore has a significantly enhanced sheen. It is somewhat thermoplastically deformable so that it can also be used, like the layers or coatings of the following Examples, for completely transparent, impressable layers or for impressabie printing inks, if colouring agents or pigments are added. It is also suitable for high-sheen wear-resistance coatings on paper or for protective coatings on printed plastics foils or shaped bodies and for metal coatings.

The prerequisites set forth in Example 1 in regard to the modifying agent and the concentration thereof also apply to this and all following Examples.

Example 3 0; 0.5 or 1.5 part of finely divided thionalide is dissolved in 10 parts of an 8% solution of a pure polyvinyl chloride powder having a K-value of at least 70 in tetrahydrofuran alone or in mixture with methyl ethyl ketone at 1:1.

The concentration of the modifying agent is in this case also below the saturation point in the solidified polymer. The lacquer or varnish produced from this solution is poured out to form a film which, after the solvent escapes, has the following refractive index nD : without modifying agent: 1.540; with 0.5 part of modifying agent: 1.605; with 1.0 part of modifying agent: 1.630.

The film is transparent and impressable without further additives and is therefore highly suitable for the use, described in Swiss patent specification No 594 936, as an intermediate layer for a flat machine-readable information carrier suitable for automatic systems, with optical markings in the form of holograms or diffraction gratings, which is applied on one side to a carrier body comprising cardboard or a plastics foil and which is provided on the other side with a transparent protective layer which has a different refractive index.

In this case, the carrier body may be printed and/or the intermediate layer with the optical impressed information can be coloured with a transparent colouring agent. In this way, the impressed location may be marked or camouflaged, as described, for reading out of the information by machine.

For the above-indicated use, it is important to use a polymer which is hard-elastic at room temperature and which has a softening point of between 60 and 20"C and a melting point of at least 150"C and which is also suitable for the production of plastics bodies and capable of being imprinted or embossed. Completely thermoplastic polymers of this kind occur in a refractive index range of 1.49 to 1.57, if they are not modified.

A further requirement is that they are substantially transparent and colourless. Besides polyvinyl chloride, the thermoplastic polymer referred to in a further Example, and also a polymer mentioned in the previous Example, comprising two components, also fulfil the above-indicated conditions.

Increasing the difference in refraction between the cover and carrier layers by means of the modifying agent in the carrier layer substantially facilitates and improves the readability of the impressed optical markings with a light-modifying relief structure. On the other hand, this permits the optical markings to be refined and also permits the use of known and novel impressing or embossing techniques. Therefore, such markings, with a protective lacquer which has a refractive index n20 of less than 1.5 can no longer be detected by eye and enhance their level of security in respect of couneReiting the damage. They permit improved mechanical reading of relief structures which operate by reflection or optical refraction, whereby for example it is possible to make savings in respect of the reflection action by means of a thin metal reflection coating.

Example 4 Coatings used for the same purpose as in the preceding Example may be produced from a mixture of 10 parts of an 8% solution in tetrahydrofuran of a pure polyvinyl chloride powder having a refractive index of 1.53 and 2 parts of a 33% solution of acridine in tetrahydrofuran.

Acridine: general formula C1sH9N, molecular weight 179.22, melting point 107 to 109"C.

The dry film has a refractive index nD of 1.611, can be impressed or embossed and can be applied to printed or unprinted cardboad and coated with protective layers of transparent plastics materials.

Example 5 A film is made from 10 parts of an 8% solution of the polyvinyl chloride from the previous Example in cyclohexanone and 2 parts of a 30% solution of pyrene in the same solvent, and used in the same manner and for the same purpose as in the previous example. The refractive index nD of this film is 1.038.

Example 6 For producing a film, in this Example, 10 parts of an 18% solution of transparent colourless polymethyl-methacrylate having a refractive index nc20 of 1.4925 in dimethylformamide is mixed with 1.8 parts of a 50% solution of N-phenylthiourea in the same solvent.

N-phenylthiourea: Molecular weight: 152.15 Melting point: 145 to 1500C The dried film of the modified plastics has a refractive index nD of 1.549. It can be used for the same purposes as that of Example 3.

Claims (13)

1. A method of obtaining a modified plastics body having a higher refractive index than the corresponding unmodified body, the unmodified body being an amorphous, transparent, colourless, hard-elastic polymer, comprising incorporating, in a solution of the polymer of at least one of the solutions of the monomer(s) from which the polymer is to be formed, a solution in a common solvent of a colourless transparent non-crystallisation-causing modifying agent and at a level of concentration that is insufficient to saturate the polymer, and removing the solvent after physical drying or after synthesis of the polymers

2. A method according to claim 1 in which the polymer used is a completely thermoplastic polymer.

3. A method according to claim 1 or claim 2 in which the proportion of the modifying agent is so selected that its mol refraction, together with the mol refraction of the polymer, additively give the desired refractive index of the plastics body.

4. A method according to any one of claims 1 to 3 in which the modifying agent is a solid organic compound that is compatible with the polymer at high levels of concentration and that, after the layer-forming operation, remains dissolved in the polymer in solid form and forms a completely transparent body.

5. A method according to claim 4 in which the modifying agent used is one or more compounds with the photochemical transitions n > z* and z

6. A method according to claim 4 in which the modifying agent used is a solid compound containing a group of the general formula:

N(C), (C)N = (C), (C) = S or (C) - Cl.

where the symbols set in brackets may be one or more chemical components that are present in a chain or at least one ring and that are denoted by the respective symbol.

7. A method according to claim 4 in which the modifying agent is thionalide, acridine, pyrene or N-phenylthiourea.

8. A method according to claim 2 or any claims dependent on it in which, for the purpose of producing impressable layered bodies, a polymerisate plastics material having a refractive index of 1.49 to 1.57, a softening point of from 60 to 1200C and a melting point of at least 1500C is used.

9. A method according to claim 2 or any claim dependent on it in which the solvent used is tetrahydrofuran, methyl ethyl ketone, cyclohexanone or dimethylformamide.

10. A method according to any one of claims 1 to 9 in which a solution of the plastics material and modifying agent is applied to a solid carrier or cardboard or a plastics foil and the solvent is evaporated.

11. A method according to claim 3 in which transparent colouring agents and/or covering pigments are also mixed with the solution of the components before processing, for the production of printing inks.

12. A method according to claim 10 in which a transparent protective layer is applied to the solidified, modified and impressed plastics layer or foil.

13. A method according to claim 1, substantially as herein described in any one of Examples 1 to 6.