SE524471C2 - Method for increasing the stability of fluorescent brighteners - Google Patents

Abstract

The present invention relates to a method for increasing the stability of fluorescent whitening agent after its preparation and during its use either on its own or mixed with other chemicals. The method is characterised in that the whitening agent is supplied with an organic acid containing aromatic group and/or can be esterified internally forming lactone, or the salt of the acid (additive A) and reducing chemical (additive B).

Description

20 25 30,,,. »« A; ; ; en (Il to .fb -fx \ J .__- Ä Prior art It has been shown that FWA as a sleeve group is unstable. By unstable is meant that the ability described above deteriorates with time, ie decreases, possibly all the way down to zero. The most common dosage form is to dissolve the agent in a liquid and a useful and common liquid is water. After applying the surface adhesive (with a very low solids content) and / or the batter (with a very high solids content such as 60-65%), the paper is allowed to dry so that the agent is contained in a solid, thin layer on the paper. known, that the stability of the agent deteriorates and that it is even degraded by such factors as daylight (the ultraviolet radiation), heat and humidity.

An article in Textile Research Joumal, 66 (7), pages 464-470, by H Ikuno, M Okuni, M Komaki and T Nakajima entitled "Photofading Behavior of Triazinylamino-Stabilized Fluorescent Brightener in Cellophane" describes how increasing humidity has a lowering humidity on FWA's illuminating ability when the agent is mixed with cellophane. It is taught that if sodium carbonate is mixed into a dye bath containing the agent in the manufacture of the cellophane, the instability of the agent in the finished product decreases. It is further stated that common salt, i.e. sodium chloride, is usually used as an additive chemical when using the agent in the treatment (coloring) of cellophane.

In a degree project from 1996 by Britt-Marie Andersson YTH-Gra fi sk Teknik, entitled “Optical brighteners, effects of temperature and humidity”, the change in whiteness of coated board samples, which contain FWA, is investigated by elevated temperature and changed humidity. It turned out that if the carton with its coating layer containing FWA was heated to temperatures of 140 ° C and above, both the lightness and whiteness of the carton decreased markedly. Furthermore, it was found that the brightness and whiteness-enhancing ability of FWA did not return at, for example, room temperature after the carton and thus also FWA had been exposed to too high a temperature, such as 140 ° C and above.

Similar friendliness at FWA is reported in the article "An Effect of Optical Brightening Agent Degradation Due to Heat and Moisture" by Nordström, J-E, P, Nordlund J .P. and Green J .P.L. TAPPI Proceedings, 1997 Coating Conference, pp. 265-280. 10 15 20 25 30 a. Now (JFI l 'Q .få .ÅÄ \ -'. L .__ \ There is also a warning that F amnesty caused by FWA in coated board occurs if the board is exposed to temperatures of 120 ° C and above Furthermore, it is pointed out that an increase in relative humidity from 0% to 50% does not have such a large negative effect on FWA.

International (PCT) patent application WO 92/01115 describes a method for improving the whiteness of a cellulosic material which either contains or has been applied to FWA. The method consists in adding a water-soluble phosphonate having 1 to 5 phosphonate groups, and / or a water-soluble carboxylate having 2 to 5 carboxylate groups, and without a nitrogen atom in the chain, at a neutral or alkaline pH. It is not claimed that these additives have a stabilizing effect on FWA, but only that the agents enhance the increase in whiteness of the cellulosic material, for example paper and cotton, which is caused by the addition of F WA.

Description of the invention Technical problem As can be seen from the foregoing, ores uorescent white matter is unstable from its preparation onwards. The circumstances that affect the instability of the subject group in itself and with regard to its brightness and whiteness-enhancing ability of the objects added and / or applied to the substance have been exemplified above.

The Solution The present invention contributes to solving this problem and relates to a method for increasing the stability of fluorescent whitening agents after its preparation and during its use alone or in admixture with other chemicals, characterized in that the whitening agent is added to an organic acid containing aromatic group and / or can be esterified internally forming lactone, or the acid salt (additive A) and reducing chemical (additive B).

It is preferred that the additive A consists of an organic acid, which contains aromatic group, or the salt of the acid. It is especially preferred that the additive A consists of an organic acid or its salt of general formula (the acid forms). o = | u 524- 4-71 4 oH oH I I c: à- c o = å à fl wR \ / 'where R; = - CHOHCHgOH or -CHOHCOOH Suitable substances within that group are ascorbic acid, arabo-ascorbic acid, sucrose ascorbic acid and xylose ascorbic acid or its salts. Very suitable is ascorbic acid and especially the L-form of the acid or its salts. The L-form is also preferred with respect to the other acids and their salts, in addition to xyloascorbic acid and its salt where the D-form is preferred.

Additive B can be any reducing agent. Examples are borohydride, dithionite, hydrazine, thiourea dioxide, formamidine sulfinic acid and hydrogen salt / salt.

Furthermore, it is possible to use catalytic hydrogenation. Preferred are the reducing agents, which are both effective and conditionally low in price. Particularly preferred are additives containing hydrogen salt and / or salt.

As for the amounts of the agents A and B to be added, the amount of A should be in a molar ratio to the amount of the bleach which is 0.1-50 to 1 and the amount of B calculated as moles should be at least the same as the amount of A. The amount of B can advantageously be seven times the amount of A.

It is already known to supplement the bleach and enhance its effect with a so-called carrier. There are a number of substances that act as carriers and an example of such is polyvinyl alcohol. This carrier can be added to the chemical mixture described above from the outset or brought into contact with the fluorescent bleach and additive chemicals of the invention when the bleach is used.

After manufacture of the fluorescent bleach, this is delivered to the user either in solid form or in the form of a liquid solution. Agents A and B can be added in solid form to the white agent while the latter is in solid form. Furthermore, all three agents can be included in a liquid solution, preferably an aqueous solution. It is also possible to wait with the addition of the agents A and B until just before or during the use of the bleach.

When using the white paper in, for example, paper / board production, the means 10 15 20 25 30 - u ~ v ~ u - -> «v v o | n - .- is added when preparing the surface glue and / or coating batter. In this context, it is also possible to apply the additives A and B separately, for example if the surface adhesive and / or the coating paste containing FWA has been applied to the paper / board.

Advantages The exemplary embodiments described later in this article show that with the aid of additives A and B it is possible to stabilize, ie to maintain to a greater extent the positive effect that ores uorescent whitening agents have in terms of brightness / whiteness of various objects, which added to the white matter. It is inevitable that this effect wears off over time, and the circumstances that are particularly contributing to the decline in power or, if desired, destabilization have been described earlier in this paper. In the practice of the invention, a stabilizing effect is obtained both in the orescent white matter per se, for example in the form of an aqueous solution, and when the white matter is applied in or on an object.

Additives A and B are not very expensive and to our knowledge they have no negative environmental impact.

Figure description Figure 1 shows the urorescence spectra of white matter-containing aqueous solutions with a certain, higher chemical concentration.

Figure 2 shows fl uroescence spectra of white matter-containing aqueous solutions with a certain, lower chemical concentration.

Best Mode for Carrying Out the Invention In the following, the invention is described in more detail with respect to certain parts and this while simultaneously reproducing experiments performed in laboratories.

Example 1 Aqueous solutions of a TINOPAL® ABP-Z Fluessing whitening agent from the company Ciba AG were prepared in a laboratory.

This chemical has a structural funnel similar to the one shown below. 10 15 20 25 (fl i * J _75 .IL * J ... sn ~ - a ø | | -. N <...... ,, no R ° ~ \ Å ts S \ o * \ oH N 1 H Two aqueous solutions with white matter were prepared, one with an amount of white matter of 0.1% by weight and the other with an amount of white matter of 0.3% by weight. a surface adhesive or a coating paste, a so-called carrier is usually used, which may be polyvinyl alcohol (PVA).

Said aqueous solutions were divided into three batches. The first batch was intact, i.e. a blank. To the second batch was added PVA (iron test) and to the third batch was added in addition to PVA also ascorbic acid of pro analysis quality - plus sodium salt - of pro analysis quality (preparation according to the invention). In the case that the white matter concentration was 0.1% by weight (%), the addition of PVA was 0.4% by weight in the two batches concerned and the addition of ascorbic acid 0.1% by weight and the sodium salt, respectively, in 0.5% by weight in the third batch. In the case that the white matter concentration was 0.3% by weight (%), the corresponding batches were 1.2, 0.3 and 1.5%. As for the preparation of the two third batches, the mixing of the chemicals took place in the following order; 1) = polyvinyl alcohol, 2) = ascorbic acid, 3) = sodium salt and 4) = FWA. Deionized water (Maxima Ultra Pure Water) was used for solution and dilution before the aqueous solutions were combined.

To protect the FWA from exposure to light, the solutions were mixed in a volumetric flask lined with aluminum foil. For the same reason, the FWA solution was involved last.

Measurements on these solutions were made with a SPEX FLUOROLOG 1680 ores uorescence spectrometer 0.22 m DOUBLE SPECTROMETER with associated computer program DATAMAX for Windows (version 2.20). In this spectrometer, the samples of light with a wavelength of 350 nanometers are excited and the ores uorescence of the samples was measured in the wavelength range from 380 nanometers to 650 nanometers.

The various sample solutions or batches were then subjected to illumination by light of a wavelength of 365 nanometers from a high pressure mercury lamp with water-cooled filters for said mercury line or wavelength for a certain time. The illumination power at said wavelength of 365 nanometers was about 240 mW / cmz. This illumination corresponds to 40 times 20 ~ 30 times normal sunlight, in the wavelengths where FWA absorbs light. After a treatment time of 15 minutes, the batches were measured as previously described. As stated earlier, there are several reasons why fluorescent bleach is destabilized. One reason is that the agent is illuminated with ultraviolet light, which as is well known is included in daylight. In this case, we have chosen the described lighting as the destabilization method.

Figures 1 and 2 show the results measured. On the y-axis, the light intensity, calculated in cps, has been plotted. cps stands for "counts per second", which can be translated as photons per second. The wavelength of the x-axis is given in nanometers.

The curves in fi gur 1 apply to the stronger chemical solution with a concentration of 0.3% of the ores uorescent white matter while the curves in fi gur 2 apply to the weaker chemical solution with a concentration of 0.1% of the ores uorescent white agent.

The same curve designations were used in the two figures. The solid curve is the zero sample, ie only the ores uorescent white matter. The curve with long lines is the batch added to PVA and which has not been subjected to destabilizing light treatment and the curve with short lines is the same batch after 15 minutes of light treatment. The dashed curve shows the batch according to the invention, i.e. which in addition to PVA also contains ascorbic acid plus reducing agent in the form of sodium salt and the dotted curve finally shows the same batch after 15 minutes of light treatment.

With regard to the results obtained, it can be stated that the carrier, which in this case is PVA, shifts the spectrum towards wavelengths (eg 430 nm) where the monomeric form of the florescent white matter fl uoresces, which is preferable from a particularly whiteness point of view. There are many chemicals and / or materials that can serve as carriers. An example is the cellulose in pulp fibers. However, cellulose is not as effective as, for example, PVA.

Regarding the samples, or batches 2 and 3, in both Figure 1 and Figure 2, the batches should primarily be compared with each other, ie the sample before it has been subjected to destabilization and after 15 minutes of light irradiation. In Figure 1, the highest fluorescence, measured for example at a wavelength of 430 nanometers, has been achieved when the fluorescent whitening agent has been added with PVA only and without irradiation (the curve with long lines). After fifteen minutes of irradiation of the sample (the curve with short lines), the light intensity has dropped drastically and more precisely 30% at the wavelength of 430 nanometers. Regarding the sample, or kit, according to the invention, the relationship is the opposite. After irradiation of the sample for fifteen minutes (the curve with dots), the light intensity at the wavelength of 430 nanometers has increased by 30% compared with the non-irradiated sample (the dashed curve). [in practice, the light intensity of the ores uorescent white matter (in admixture with carriers, for example) just when an object, for example cardboard in the form of a cardboard web, has been added or applied, is uninteresting. It is the time when the object, for example the cardboard, is to be used that is of interest and it is the brightness / whiteness of the object at the time that counts. If, after all, an iron transfer is made between batch 2 and batch 3 after 15 minutes of light irradiation at a white matter concentration of 0.3%, ie according to fi gur 1, it is assumed that the light intensity at, for example, a wavelength of 430 nanometers is slightly higher for the batch prepared according to the invention than for the batch containing only white matter and carrier.

If one looks at wavelengths above 430 nanometers, the advantage of the batch prepared according to the invention is marked.

Similar results are obtained with a weaker white matter solution (0.l% white matter), as shown in Figure 2. However, it can be stated that all curves for sentences 2 and 3 are much closer to each other in this figure than is the case for the corresponding curves in Figure l.

Example 2 The following experiments were performed in the laboratory of a board mill.

Solid cardboard of standard quality, with a basis weight of 240 g / mz and pre-coated with a standard pre-coating batter in two batches with a batter spread of 10 and 6 g / mz, respectively, was removed at the mill. No lignin-containing pulp fibers were used in the various layers, which amounted to a number of five. Only bleached sulphate pulp was included in the various pulp sources, including both softwood pulp and hardwood pulp. All masses had a brightness exceeding 88% ISO.

In a bench coater in the laboratory, samples of the above-mentioned cardboard were coated after conversion to A4 size with two different coating sheets, in a spread of 13 g / m 2.

One batter, which was a standard coating batter, contained the following ingredients: 70 parts calcium carbonate in the form of ground marble (of type Hydrocarb) 30 parts of clay (of type Kao fi ne) 16 parts of latex 0.8 parts of polyvinyl alcohol 10 15 20 25 30 ~ - ~ » | ~. . - ~ | .u 0.4 parts thickener (carboxymethylcellulose) 0.2 parts hardener in the form of ammonium zirconium carbonate (of type Bacote) 0.2 parts of FWA (of type Blankophor ® P Liquid) As for the fl uorescent bleach, the formula and its chemical structure are shown in the description in example 1.

In absolute weight, the batter contained 1 gram of the agent based on 500 grams of pigment, i.e. calcium carbonate plus clay.

A number (10) of cardboard samples were coated with this batter and they were air dried in the laboratory at room temperature.

The same number of carton samples was coated with a batter of the composition described above and provided with two additional chemicals according to the invention, namely 3 grams of ascorbic acid and 17 grams of sodium salt (NazSOg) based on 1 gram of FWA, which may be called the other batter. The carton samples were then allowed to air dry in the laboratory at room temperature.

The dry cardboard samples were exposed to light in a Suntest XLS + test chamber for 24 hours. The light is generated by a xenon lamp, whose light is similar to that of the sun.

However, some light wavelengths must be filtered out. This is done with a glass filter that transmits ultraviolet (UV) light. In the experiments, an alter was used, which filters out light with a wavelength of less than 320 nanometers, which light is similar to the light in a shop window.

The power of the xenon lamp was 600 W. One hour of light exposure in the test chamber corresponds to a time period of approximately 3.5 days in daylight.

A number of interruptions in the light exposure of the carton samples were made to measure these optical properties. What was measured was brightness, whiteness and wavelength-resolved rectitude. The measurement was made with Elrepho SF45O from Datacolor International. Measurements were also made on the cardboard samples before these were stuffed into the test chamber.

Table 2 below shows the measured D65 brightness and whiteness values according to CIE for each carton test series. CIE, which stands for "Commission Intemationale de l'Eclairage", reports the spectral energy distribution for a number of different standard lights. A corresponds to ordinary light bulb light, C corresponds to daylight on the back of a sunlit object and D65 is the same as C, but with a slightly increased ultraviolet component. 10 15 _25 (J) (D |... N 10 Table 2 Exposure time in Cardboard sample with layer Cardboard sample with layer hours containing FWA stabilized containing non-stabilized F WA according to the invention Brightness Whiteness Brightness Whiteness 0 96.9 108.8 96.7 106.9 1 94.4 102.1 91.1 92.9 2 93.4 99.2 90.0 89.9 4 92.3 96.0 89.4 87.9 8 91.5 93.5 89.1 87.0 12 91.1 92.0 88.7 85.8 16 90.7 90.9 88.6 85.5 20 90.5 90.4 88.5 85.1 24 90.6 90.7 88.3 84.8 As can be seen, the additive chemicals have a possible initial (see values for 0 hours) positive effect In terms of brightness and whiteness, only 0.2 units differ in brightness, which may be within the margin of error, but in terms of whiteness, the increase is 1.9 units.

In the case of cardboard samples, which contain layers of unstabilized FWA, one hour of light exposure has led to a 5.6 unit decrease in brightness and a full 14 units decrease in whiteness. This is thus a dramatic reduction in whiteness in particular.

The corresponding reductions in the cardboard samples that have layers with FWA, which have been stabilized according to the invention, are 2.5 units and 6.7 units, respectively.

After twenty-four hours of light exposure of the carton samples, the brightness and whiteness of the carton samples with a layer containing FWA stabilized according to the invention decreased by 6.3 and 18.1 units, respectively, while the corresponding decreases of the carton samples with layers containing unstabilized FWA are 8.4 and 22.1 units, respectively. In other words, the carton samples where the invention has been applied in comparison with the reference samples have a brightness which is just over two units higher and a whiteness which is six units higher.

LI! 15 20 ~. | «F. o u ø o n »11 Example 3 Solid quality cardboard was once again taken out of the mill. Details of the carton are given in Example 2. However, the carton is not pre-coated in this case.

After conversion of the carton to A4 size samples, the samples in the said bench coater in the laboratory were coated with the standard coating batter as shown in Example 2 and with such batter supplemented with additive chemicals according to the invention in four different additive levels. These different levels were 0.5 g ascorbic acid plus 2.5 g sodium salt, 1 g ascorbic acid plus 5 g sodium salt, 2 g ascorbic acid plus 10 g sodium salt and 4 g ascorbic acid plus 20 g sodium salt per gram of FWA.

The handling of the carton samples and the light exposure of them corresponded to what was reported above. However, the exposure time was extended to 48 hours. Furthermore, the brightness measurement according to ClÉE D65 was changed to measurement according to ISO. Furthermore, a cardboard sample series was placed in a heating oven where the temperature was set at 80 ° C in order to investigate how elevated temperature affects the course of the decrease in brightness and whiteness over time. Even in this case, the exposure time was up to 48 hours.

Table 3 below shows how the brightness and whiteness of the different carton samples change according to the light exposure time and in Table 4 how these parameters change according to the time the carton samples have been in a temperature of 80 ° C. In these tables, the cardboard samples which show a coating layer with only FWA have been referred to as reference. Furthermore, the addition of ascorbic acid in grams based on 500 grams of pigment is stated in the coating batter. 10 15 20 524- 471. o o ~ | now 12 Table 3 Exposure time Brightness, ISO Whiteness, CIE in hours Ascorbic acid amount Ascorbic acid amount Ref. 0.5 g lg 2 g 4 g Ref. 0.5 g 1 g 2 g 4 g 0 89.7 90.5 90.9 90.4 90.4 105.0 107.6 108.5 106.0 105.8 1 86.2 88.8 89.4 89.7 89.8 97.6 99.4 100.7 103.2 102.3 2 87.9 88.4 89.0 89.3 89.3 95.6 97.1 98.1 100.4 99.4 4 87.6 88.2 88.5 89.1 88.6 93.4 95.0 98.5 95.5 6 - - 88.4 - 88.5 - - 94.1 - 94.9 8 87.4 87.7 - 88.6 - 91.4 92.3 - 95.8 - 15 - - 87.7 - 87.7 - - 89.8 - 90.5 16 87.7 87.9 87.4 88.7 87.3 89.7 90.3 87.5 93.1 87.7 24 87.5 87.7 - 88.4 - 88.1 88.9 - 91.2 - 48 87.3 87.3 - 87.9 - 86.1 86.0 - 87.8 - Table 4 Storage time in Brightness, ISO Whiteness, CIE hours Ascorbic acid amount Ascorbic acid amount Ref. 0.5 g lg 2 g 4 g Ref. 0.5 g 1 g 2 g 4 g 0 89.9 90.4 90.5 90.4 90.3 105.8 107.1 107.6 105.1 105.4 1 89.8 90.3 90.3 90.2 90.2 104.9 106.3 106.6 104.4 104.9 2 89.6 90.2 90.1 90.1 90.0 104.4 105.8 106.1 104.1 104.4 4 89.7 90.2 90.3 90.2 90.2 104.5 106.0 106.4 104.3 104.9 8 89.4 89.9 90.0 90.0 90.1 103.6 105.2 105.7 103.8 104.3 16 89.9 90.7 90.8 90.8 90.7 104.3 106.5 107.2 105.2 105.8 24 89.7 90.5 90.7 90.8 90.7 103.7 106.1 107.1 105.0 105.6 48 89.3 90.3 90.3 90.5 90.5 102.3 105.2 105.8 104.3 105.3 10 m ha - r> JS w -_Ä ~ ~ - - »o. «N n | .u 13 If the results in Tables 3 and 4 are compared, it is found that the actual light exposure has a more degrading effect on the ores-uorescent white matter than a temperature increase to 80 ° C. Even in these experiments it turns out that the additives ascorbic acid and sodium salt stabilize the fluorescent white matter, although the effect in these experiments is not as pronounced as in the experiments according to Example 2. That a certain level of addition of these agents gives an optimal effect can not be clearly stated in these experiments. However, it seems that an addition amount of 1 to 2 grams of ascorbic acid per gram of FWA is sufficient. The amount of additive of the reducing agent must be at least the same as the amount of the additive of the organic acid, for example ascorbic acid, and preferably seven times this amount.

Claims (8)

10 15 20 25 30 a u o 1 nu i. | «U c 4 n- PATENT REQUIREMENTS 1. l. Method for increasing the stability of oresorescent whitening agents after their preparation and during use alone or in admixture with other chemicals, characterized in that the whitening agent is added to an organic acid which contains aromatic group and / or can be esterified internally forming lactone, or acid salt (additive A) and reducing chemical (additive B). 2. A method according to claim 1, characterized in that the additive A consists of an organic acid containing aromatic group or the salt of the acid. 3. A method according to claim 1, characterized in that the additive A consists of an organic acid or its salt of general formula (the acid form) (|) H (|) H i = T where R 1 = -CHOHCHZOH or -CHOHCOOH. 4. A method according to claim 3, characterized in that the additive A consists of ascorbic acid or its salt. 5. A method according to claims 1-4, characterized in that the additive B consists of a chemical containing hydrogen salt and / or salt. 6. A method according to claims 1-5, characterized in that the additive A is supplied in an amount in a molar ratio to the fluorescent glass agent, which is 0.1-50 to 1, and the additive B is supplied in an amount calculated in moles, which is at least the same as the quantity calculated in moles of the additive A. 5: .- "| in. 3. .f. 15 7. A method according to claims 1-6, characterized in that a carrier is also included in or brought into contact with the chemical mixture. 8. A method according to claims 1-7, characterized in that the fluorescent whitening agent and the additives A and B are mixed into surface adhesive and / or coating paste, which is applied to the surface of paper / cardboard.