FI63959B - FOERFARANDE FOER ATT GOERA EN YTA AOTMINSTONE PARTIELLT FOSFORESCERANDE - Google Patents

Description

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United Kingdom-United Kingdom (GB) 3U78 / 7U

(71) The Post Office, 23 Howland Street, London, W1P 6HQ, England-England (GB) (72) Berkeley Michael Ferro, Bamehurst, Kent, Rodney Edwin Spratling, Sittingbourne, Kent, Aubrey Douglas Walker, North Harrow, Middlesex,

England-England (GB) (7U) Berggren Oy Ab (5U) Method for making a surface at least partially phosphorescent -! Förfarande för att göra en yta ätminstone partiellt fosforescerande t (62) Separated from application 750197 (publication 63593) -

This invention relates to a process for making a surface at least partially phosphorescent.

It is known that certain organic compounds, which may or may not be fluorescent when irradiated with short wavelength light, exhibit phosphorescence during irradiation and after dispersion in a suitable solid matrix, such as solid solutions or adsorbents. Such compounds are known as phosphorescence activators. It is known that organic phosphorescence (radiative attenuation of the excited triplet state) does not occur in the liquid phase, where non-radiative attenuation modes of the relatively long-lived triplet state are more favorable. Phosphorescent printing inks and coating compositions currently available therefore contain solid particles of phosphorescent material dispersed in suitable liquid media.

British Patent No. 870,504 describes a phosphorescent material formed by reacting formaldehyde in the liquid phase

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2,695,99 with the substance with which it reacts to give a solid condensation product, especially in the presence of an amino compound such as urea or melamine phosphorescence activator to form a strongly phosphorescent solid condensation product. The phosphorescence activator is held in a solid matrix of formaldehyde resin. The material of English Patent No. 870,504 is an excellent brightener; it has a high moisture resistance and if deactivated by humid conditions it can be reactivated by drying. This material can be used as a phosphorescent ink after it has been ground to form a fine powder and dispersed in a liquid.

According to the present invention, there is provided a method of rendering a surface at least partially phosphorescent, comprising applying to the surface a mixture comprising a phosphorescent activator and a reaction product of formaldehyde and melamine or urea, the method comprising (a) applying to the surface a mixture comprising a water soluble formaldehyde and melamine or urea precondensate aqueous solution, which precondensate is still capable of reacting fosforointiaktivaattorin in the absence of forming an insoluble condensation product, which mainly does not absorb the ultraviolet radiation of any wavelength, which fosforointiak-activator substantially absorbs ultraviolet radiation and is still capable of reacting fosforointiaktivaattorin in the presence of forming a phosphorescent insoluble condensation product, and ( b) forming a phosphorescent insoluble condensation product in situ on the surface by causing said further reaction to either o evaporating the solvent at ambient temperature or exposing the surface to an elevated temperature, preferably in the presence of a substance which catalyzes a further reaction.

The soluble condensation product is generally a low molecular weight material. The insoluble condensation product having a high molecular weight is hereinafter referred to as a resin. The formation of the resin from the prepolymers usually takes place by crosslinking.

In a preferred embodiment, one of the components that is reacted to form the prepolymer and then the resin is formaldehyde. Suitable substances with which formaldehyde reacts to form a solid resin via a soluble prepolymer are amino compounds, in particular urea and in particular melamine.

As disclosed in British Patent No. 870,504, melamine-formaldehyde resins are more moisture resistant than urea-3 63959 formaldehyde resin; this is advantageous in the context of the present invention due to the moisture sensitivity of the phosphorescence. Resins formed from phenolic compounds and formaldehyde are unsuitable for use with most phosphorescence activators due to their ultraviolet adsorption in the spectral range of 250-380 nm.

A solution of a phosphorusation activator and an amino-formaldehyde precondensation suitable for use in the process of the invention is disclosed in Patent Application No. 750197.

The formation of an insoluble resin from formaldehyde and an amino compound, for example melamine, takes place through two different chemical reactions, which are favored by different reaction conditions. The first step involves a reaction between the components to give a mixture of monomeric and / or oligomeric methylated melamines; these products form a prepolymer. Neutral or alkaline conditions favor the formation (methylolysis) of the prepolymer. The second step is the crosslinking of methylolated monomers and oligomers to give a high molecular weight resin; this reaction is favored by acidic conditions.

For the purposes of this invention, the best results are obtained and the methylolation reaction takes place substantially completely before crosslinking begins, since the reactivity of the resin-forming monomers and oligomers (prepolymer) is determined by the amount of methylolysis. The higher the reactivity of the methylolized prepolymer, the higher the density of the bridges and thus the moisture resistance of the resin.

The solvent in which the activator and prepolymer are dissolved may suitably be water or water mixed with an alcohol, preferably an aliphatic alcohol having 1 to 4 carbon atoms. The solution contains one or more stabilizers to prevent premature conversion of the prepolymer to the final desired cured resin.

In one embodiment, the composition used in step (a) may be a coating composition for coating the surface of the paper to be printed; such paper can be used, for example, to make stamps. In another embodiment, the composition of the invention may be a printing ink that can be used, for example, to print phosphorescent color streaks on postage stamp sheets and to apply address codes to the post for use in automatic sorting.

Step (b) can be performed by various methods; for example, evaporation of the solvent may be sufficient to cure the resin or the surface itself may have properties, e.g., pH, that cause it to catalyze the reaction. Curing can be performed by exposing the surface to an elevated temperature; if necessary, a curing agent may be added to the mixture before it is applied to the surface.

Any substance capable of maintaining phosphorescence when dispersed in a solid matrix can be used as the activator. Suitable activators are mainly aromatic compounds, which may be benzene-structured, heterocyclic or fused ring compounds. Aromatic amines, carbonyl compounds, carboxylic and sulfonic acids, ethers and phenols are particularly good activators; examples of such compounds are listed in British Patent No. 1,002,022.

Depending on the activator used, the phosphorescence material of the invention can be excited with either long (365 nm) or short (254 nm) wavelength ultraviolet light. Here are some examples:

Long wavelength (365 nm) activators

Carbazole sulfonic acid (blue afterglow)

Para-aminobenzophenone (green afterglow) α-naphthoplavone (yellow afterglow) 8-amino-1-naphthol-3,6-disulfonic acid (orange-yellow afterglow) 2-naphthylamine-6-sulfonic acid (yellow-green afterglow)

Short wavelength (254 nm) activators

Para-aminobenzoic acid (purple afterglow)

Terephthalic acid (blue-violet afterglow)

Fluorosulfonic acid (teal glow)

Diphenylene oxide sulfonic acid (blue afterglow) 4,4'-dihydroxydiphenylsulfonic acid (blue afterglow)

Light-containing short-wavelength activators are generally unaffected by long-wavelength ultraviolet light, but long-wavelength-tuned lighters show a measurable response to short-wavelength light. Nevertheless, it is still possible to make two separate sets of phosphorescent labels for one piece and read them separately. For example, if one code character is first applied as containing a short wavelength tuned light, it can be detected by a suitable amplification light cell for encoding, and then another set of characters is applied as containing a long wavelength tuned light. These can be stated without the signs of the first set interfering with the finding.

For example, stamps can be printed using a short-wavelength tuned light that allows letters and other postal items to be separated into first and second class mail and then translated "in the right direction", i.e. to stack an address up on a postage stamp in the upper right corner? the address code marks for automatic sorting can then be applied using a long wavelength tuned light material so that the light material of the stamp does not interfere with the sorting process.

As mentioned above, in one embodiment, the invention relates to printing ink and printing of phosphorescent indicia on a surface, in particular on paper. The ink of the invention can be prepared, for example, by reacting a suitable excess of an amino compound, preferably melamine, with formaldehyde in aqueous solution in the presence of a phosphorescence activator at a pH above 6 and preferably at a pH of about 9. The pH can be maintained at about 9 with sodium carbonate / sodium borate buffer. . The molar ratio of melamine to formaldehyde is preferably between 1.1: 1 and 1.5: 1. By carefully adjusting the reaction conditions, especially the temperature and pH of the solvent, a low viscosity solution containing about 20% by weight of a prepolymer with a relatively low molecular weight can be obtained. The solution may be stabilized by the addition of an alcohol, preferably methyl, ethyl, isopropyl or n-butyl alcohol, more preferably up to 20% by volume and most preferably 10-15% by volume. Inks that differ slightly in properties such as surface tension and viscosity can be obtained by varying the composition. The convenient inks of the invention may have a shelf life of at least 6 months under normal storage conditions without vulcanization of the prepolymer.

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The printing ink used in the method according to the invention may be completely free of particles and is therefore very suitable for use in jet printing machines; conventional particulate light ink inks tend to clog the nozzles of jet printing machines as the particles agglomerate. Forced drying of the printed surface can be used to accelerate solvent evaporation and resin vulcanization; for example, an infrared beam may be used which is parallel to and slightly above the surface and aligned above that printing area so that the ink droplets are almost dry when they hit the surface. The use of a beam parallel to the surface ensures that the surface itself is not damaged; such a system can be achieved using suitable reflection and alignment equipment. The use of weakly acidic paper also accelerates vulcanization.

In another embodiment, the invention relates to a total coating of paper which can be made phosphorescent by exposing it to ultraviolet radiation. The invention thus provides for use a paper coating composition comprising a solution of the invention, preferably an aqueous solution mixed or in combination with one or more pigments and / or binders and / or other components commonly used in a paper coating composition. The coating composition of the invention can be prepared by mixing a prepolymer solution of the invention with a conventional coating composition, which generally consists of an aqueous suspension of pigments, binders and other additives. The wet coating composition should preferably not contain more than 20% by weight of the prepolymer solution, otherwise difficulties may be encountered when printing on coated papers.

If desired, a curing agent (crosslinking agent) can be added to the prepolymer solution immediately before mixing into the coating composition.

The coating composition can be applied to paper using conventional equipment; the coated paper can then be dried, for example, by passing it through a heated oven or over heated rollers: If the degree of heating is insufficient to completely vulcanize the resin at this stage, the vulcanization continues slowly at room temperature.

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The preparation of an aqueous solution of amino-formaldehyde precursor / phosphorusation activator for use in the paper coating composition is preferably carried out in the pH range of 6-9 and preferably in the range of 6-8 and most preferably in the range of 6-7 ° C, preferably at 75-80 ° C, e.g. . The higher the pH of the reaction mixture, the longer the reaction takes place at any temperature and the more precisely the reaction rate of the final product can be controlled. The pH can be adjusted, for example, with sodium hydroxide or calcium carbonate. In the case of calcium carbonate, the pH can be maintained at about 6.2 by maintaining an excess of this reagent in the mixture.

The degree of reaction in the formation of the soluble prepolymer is important and can be easily controlled by measuring the miscibility of the reaction mixture with water, i. titrating with water until the mixture becomes cloudy due to precipitation of the solid resin; the maximum volume of water into which one volume of the prepolymer solution can be mixed without causing turbidity is commonly referred to as the water resistance of the solution. Alternatively, the reaction rate can be controlled by measuring the viscosity of the reaction mixture. This method must be used if calcium carbonate is used to adjust the pH, as an excess of this reagent makes the solution cloudy so that its water resistance is difficult to determine.

The conversion of the precondensation product to a solid resin is preferably promoted by the addition of a catalyst to promote crosslinking of the prepolymer, immediately before the prepolymer solution is added to the other components of the coating composition; the catalyst is preferably an acid, for example sulfuric or acetic acid.

The degree of reaction in the formation of a soluble condensation product (prepolymer) is important if it is to be used in a coating composition, because if it does not react sufficiently at this stage, the resistance of the final coating to moisture-induced phosphorescence deactivation deteriorates. a homogeneous mixture with the coating composition and the product then has unsatisfactory coating and printing properties. Thus, the most satisfactory results are obtained when the reaction is allowed to go as far as possible in a manner consistent with a homogeneous coating composition. The permissible reaction rate depends on the nature of the pigment / binder system used 8 63959 and also on the solids content of the mixture.

For the preparation of a typical coating composition having a dry matter content of 50% and containing 15-20% of a prepolymer solution, a solution having a water resistance of 2.0-2.5 volumes of water per volume of prepolymer solution is suitable. The viscosity corresponding to this water resistance depends on the pH of the prepolymer solution. Examples of approximate viscosity values together with reaction times at different pH values to complete the prepolymer step are given below: pH Temperature Reaction time Prepolymer solution (min) viscosity at water limit (cP) 8.5 75 ° C 190 13-15 7.4 75 ° C 60 10- 12 6.0 75 ° C 25 7-9 9.0 92 ° C 70 12-14

The paper coated with the coating composition according to the invention can be used, for example, for the production of stamps; for this purpose, it is recommended to use a short-wavelength tuned activator, for example p-aminobenzoic acid (PAB) or terephthalic acid (TPA), to prevent interference in automatic sorting processes using long-wavelength tuned address code markings.

The following examples illustrate the invention; Example 3 refers to Figures 1 and 2 of the accompanying drawings.

Example 1 Preparation of printing ink 850 g of melamine (1.3 mol) were mixed with 400 g of a 37% aqueous formaldehyde solution (1 mol), the suspension was stirred and 300 ml of a buffer solution (sodium carbonate / sodium borate, pH 9.2) was added to pH n. 9 to achieve. Then 20 g of the sodium salt of carbazolesulfonic acid (based on about 14% by weight of formaldehyde) were added and sufficient water was added to give a total volume of liquid of about 2 1/2 liters. The suspension was stirred and refluxed and this temperature was maintained at 50-60 63959 for 9 minutes. The heat source was removed and 300-400 ml of methanol was added. Stirring was continued until the mixture had cooled. It was allowed to stand at room temperature for about 18 hours. The liquid was then decanted; this gave 2 1/2 liters of ink.

The recovered solid (350 g) was washed with a 50/50 mixture of alcohol and water, dried and reused as follows: 350 g of the recovered solid was mixed with 450 g of fresh melamine; 300 ml of pH 9.2 buffer and 350 g of 37% aqueous formaldehyde were then added. After the sodium salt of carbazolesulfonic acid and water were added to the mixture, the preparation was carried out as described above. An additional catch of about 2 1/2 liters of ink was obtained.

The aqueous ink had a low viscosity and contained n.

20% by weight of a rather low molecular weight aqueous polymer. About 10-15% by volume of alcohol was added as a stabilizer and the solution was stored for six months; no clear increase in viscosity had occurred at the end of this time.

The ink was applied to the paper as a thin film; it became stain-free in about a second and became increasingly phosphorescent as it dried. When the film was moistened, the phosphorescence was extinguished but after drying the film was again phosphorescent.

Example 2

Preparation of the paper coating mixture 24 g of p-aminobenzoic acid and 6.5 g of sodium hydroxide were dissolved by heating in 75 ml of water; the pH of this solution was about 9. The solution was added to 1.8 liters of 40% aqueous formaldehyde, the mixture was heated to 75 ° C and the pH was adjusted to 8 by further addition of alkali. 1.2 kg of melamine powder was added and the temperature of the mixture was maintained at 75 ° C with efficient stirring. The melamine dissolved to give a clear yellow solution after 10-15 minutes. The pH of the solution was maintained at 8.

Half an hour after the addition of melamine, a 10 ml sample was taken from the solution and titrated with water until the solution became cloudy.

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ίο 63959 Samples were taken at 10-15 minute intervals. As the reaction progressed, the amount of water required to precipitate the solid resin from the solution decreased and the viscosity of the prepolymer solution increased. After the reaction had progressed to the point where 2 1/2 to 3 volumes of water were sufficient to cause turbidity in one volume of solution, the solution was continuously stirred with stirring into an aqueous coating mixture consisting of pigment and binder as described above. The resulting wet coating composition contained about 20% by weight of the prepolymer solution.

Example 3

A series of experiments were performed in which solutions were prepared according to the procedure of Example 2 under different pH and temperature conditions: a) Temperature 75 ° C, mixture pH 6.1 b) Temperature 75 ° C, mixture pH 7.4 c) Temperature 75 ° C, mixture pH 8.5 d) Temperature 92 ° C, mixture pH 9.0.

The amount of water needed to make the reaction mixture cloudy was measured as a function of reaction time; the results are shown in Figure 1 of the accompanying drawings, where t is the reaction time in hours and V is the number of volumes of water needed to produce turbidity in one volume of reaction solution. It was found that a prepolymer solution having a degree of reaction in the range above line A produces a uniform homogeneous coating composition when mixed with a conventional coating composition containing appropriate amounts of pigment and binder. Solutions with a reaction rate in the range below line B do not produce satisfactory coating compositions. Fairly thick but otherwise satisfactory mixtures are obtained between lines A and B.

It can be seen that of the four sets of reaction conditions tested, pH 8.5 and temperature 75 ° C gave the slowest and thus best controlled reaction.

Figure 2 shows the viscosity of the reaction mixture as cP as a function of the reaction time in t hours. In addition to the four runs a) to d), the fifth run e) was performed at pH 9.7 and 75 ° C. The shaded portion of each curve indicates where the resin solution produced a thick or unsatisfactory coating composition.

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Example 4 Alternative Procedure for Preparation of Coating Mixture 24 g of p-aminobenzoic acid was dissolved in 200 ml of hot water and the doped calcium carbonate solution was added slowly until effervescence ceased; about 25 g of calcium carbonate was needed. The pH of the solution was about 6.2.

The activator solution was added to 1.8 liters of a 40% aqueous formaldehyde solution and the pH was maintained at 6.2 by adding more calcium carbonate as needed.

Melamine (1.2 kg) was added and the reaction was carried out at 75 ° C as in Examples 2 and 3. However, at this pH, the reaction proceeds faster than at the higher pH used in the previous examples; it was gone in 20-30 minutes.

The degree of reaction was controlled by measuring the viscosity of the solution. The end point was considered to be when the viscosity of the solution was 10-12 cP. The coating composition was then prepared as described in Example 2.

Example 5

Preparation of a coating composition containing an acidic vulcanizing agent An activator solution was prepared by dissolving 30 g of p-aminobenzoic acid and 8 g of solid sodium hydroxide in 250 ml of water with heating; the pH of the solution was about 7. 130 ml of this solution was added to any formaldehyde and the pH was adjusted to about 6.5.

The temperature of the mixture was raised to 75 ° C and 1200 g of melamine powder was added with constant stirring. The reaction of the melamine / formaldehyde mixture to the prepolymer step was continued with stirring at 75 ° C until the water resistance of the solution, as described above, was about 2 1/2: 1. The time required for the reaction was approximately 40 minutes. Sulfuric acid (24 ml of a solution prepared by mixing 100 ml of concentrated sulfuric acid and 750 ml of water) was added to the solution with vigorous stirring, and immediately afterwards the resulting solution was added to approximately 15 kg of coating mixture with the ratio of solution to coating mixture selected to give the required fosforesenssivoimakkuuden.

Claims (5)

12,. 63959 A method of making a surface at least partially phosphorescent, comprising applying to the surface a mixture comprising a phosphorusation activator and a reaction product of formaldehyde and melamine or a urea, characterized in that (a) A mixture comprising a phosphorusation activator and a water-soluble formaldehyde and melamine or urea precondensate of an aqueous solution of precondensate can react further fosforointiaktivaattorin in the absence of forming an insoluble condensation product, which mainly does not absorb the ultraviolet radiation of any wavelength, a phospho-rointiaktivaattori substantially absorbs ultraviolet radiation and is still capable of reacting fosforointiaktivaattorin in the presence of forming a phosphorescent insoluble condensation product, and (b ) a phosphorescent insoluble condensation product is formed in situ on the surface by causing said further reaction either by evaporating the solvent at ambient temperature or by exposing the surface to an elevated temperature, preferably in the presence of a substance that catalyzes a further reaction. A method according to claim 1, characterized in that the mixture is used as an ink and is applied to the surface by ink jet printing. Process according to Claim 1, characterized in that the mixture is used in a paper coating mixture to which, before step (a), a catalyst is added to form an insoluble condensation product, preferably an acid catalyst. A process for the preparation of a phosphorescent batch of acetaldehyde, which comprises a mixture of phosphorescent activators and a reaction product of formaldehyde and melamine or urea, with the addition of a chemical in the form of an applicator and a composition comprising a formate dehydrogen and a melamine or urea, a formate dehydrogen and a melamine or urea,