EP0111943B1 - Developer resin for leuco dyes - Google Patents

Description

The invention relates to resins for developing leuco pigments, in particular for developing colors in pressure-sensitive recording materials.

Pressure sensitive recording materials such as e.g. Carbonless papers are coated foils with which carbonless copies can be made without the use of a color insert, e.g. of carbon paper.

The recording is carried out by developing a color image from a colorless organic compound which is dissolved in a high-boiling organic solvent and is capable of forming a color.

This organic compound is called leuco pigment. The most common leuco pigments are crystal violet lactone or malachite green lactone. However, other such connections are also used, e.g. Leukauramines, acylauramines, basic, unsaturated aryl ketones, basic monoazo compounds, rhodamine B-lactams, Michler's hydrol, carbinols of crystal violet and machalite green or pyrans.

The color development takes place by reaction of these leuco pigments with an acidic developer substance with intimate contact of these reactants. The contact is normally made by the writing pressure on appropriately coated foils, but also, for example, when thermocopying due to localized heat and the resulting reaction of the leuco pigment.

As developer substances one knows acidic, inorganic salts, such as. B. acidic clays or salts of strong organic acids and weak bases, free organic acids or phenol derivatives. In addition to a tendency towards moisture absorption, which usually leads to an unclear typeface, these substances have the disadvantage that they have to be fixed on the film with the aid of a binder. In contrast, the direct use of acidic polymers as color developers is much more advantageous. Phenol-containing polymers such as phenol-aldehyde condensation resins and phenol polymerization resins are preferably used as developer resins of this type.

Phenol-aldehyde condensation resins have the disadvantages that, on the one hand, the papers coated with them slightly yellow and that there are toxicological concerns during recycling because there is a risk of formaldehyde being split off.

As phenol polymerization resins for this purpose are those by copolymerization of phenols with acetylene under pressure and at a higher temperature, i.e. H. Expensive alkylphenol acetylene resins and di- and oligomeric alkenylphenols produced under conditions which are not problem-free are known.

For example, DE-OS 2647696 and DE-OS 2703 574 disclose dimeric substituted alkenylphenols and in EP-A-0029323 vinylphenol oligomers as color developers for leuco pigments. In addition to the disadvantage that these products are also quite expensive, they have the difficulty that they have a relatively high softening point, which moreover cannot be changed in the desired range.

From EP-A-0029323 it is known to change the softening point of oligovinylphenol by varying the degree of polymerization, but the unsubstituted dimer of vinylphenol already has a softening point of 95 ° C., while more polymerized vinylphenol or the dimers of the substituted vinylphenols have a higher softening point to have. For pressure-sensitive recording materials, however, the softening point should be in the range from 55 to 110.degree. C., but preferably in the range from 70 to 90.degree. C., in order to have optimal dissolution behavior in the solvent of the leuco pigment and thus good color development.

It is therefore an object of the invention to provide an inexpensive resin for developing leuco pigments, in particular for developing colors in pressure-sensitive recording materials, based on a phenol-containing polymer which is simple to produce and handle, which does not cause yellowing of the recording material, and no toxicological concerns Usage or recycling can be expected and its softening point is in the range of 55-110 ° C (according to K.-S), but is preferably in the range of 70-90 ° C. This object is achieved by resins and processes for their production according to claims 1-6.

Phenol-modified hydrocarbon resins are commonly used polymers in the adhesives and coatings industry, which are produced by polymerizing unsaturated aromatic hydrocarbons and phenol or substituted phenols using Friedel-Crafts catalysts.

They are less suitable as developer resins for leuco pigments because their content of phenolic hydroxyl groups, which is indicated by the size OH number, is too low for good color development. If one tries to increase this OH number by increasing the proportion of phenol, the excess phenol is no longer bound from an OH number of about 3.5. The resins become unstable, which is noticeably noticeable due to the smell of free phenol.

However, it has been found that stabilized phenol-modified hydrocarbon resins with a high OH number and produced according to the earlier applications EP-A-70579 and EP-A-109694 have very good development properties, but are not suitable as development resins in pressure-sensitive recording materials due to their low softening points.

These stabilized, phenol-modified hydrocarbon resins are produced by polymerizing unsaturated, aromatic hydrocarbons, optionally isobutene, and phenol or substituted phenols Use of Friedel-Crafts catalysts, with a subset of the unsaturated aromatic hydrocarbons and / or the entire amount of phenols and catalyst being introduced and the polymerization being controlled by adding the remaining unsaturated aromatic hydrocarbons in such a way that after reaching the chosen polymerization temperature, which is in the range of 70 to 140 ° C, isothermally.

EP-A-70579 and EP-A-109694 belong to the prior art under Article 54 (3) EPC, EP-A-70579 the contracting states DE, FR, GB, IT and NL and EP-A-109694 the contracting states BE , DE, FR, GB, IT and NL.

The ratio of phenol or phenol mixture to unsaturated aromatic compounds must be adjusted so that stoichiometric addition products with a corresponding OH number can form. For the use according to the invention of these stabilized phenol-modified hydrocarbon resins, an OH number of 4.5 is already sufficient for color development, but in general the color development becomes better the higher the OH number.

Phenolic compounds, polymerizable unsaturated, aromatic hydrocarbons and possibly isobutene are used as raw materials for the resins according to the invention. Both mononuclear and multinuclear phenols, such as the phenol itself, its alkyl-substituted homologs such as cresols or xylenols and naphthols, as well as halogen-substituted phenols such as chloro- or bromophenol and polyhydric phenols such as resorcinol or catechol can be used as phenolic compounds.

Technical phenol fractions which are obtained in the distillation of crude phenol are preferably used. These contain phenol, cresols, xylenols and possibly small amounts of higher alkylated phenols. The composition of these fractions varies depending on the boiling range selected.

Unsaturated, aromatic hydrocarbons are found on the one hand in the distillates from the high-temperature tar boiling in the temperature range from 140 to about 220 ° C, on the other hand, unsaturated, aromatic hydrocarbons are formed in the cracking of naphtha or gas oil and in the pyrolysis of cracking residues and are in the range of 160-220 ° C boiling fraction, the so-called resin oil fraction, enriched. These fractions contain unsaturated aromatic compounds, essentially indene, vinyltoluene, methylinden, coumarone, dicyclopentadiene, methyldicyclopentadiene, styrene and a-methylstyrene, in a concentration of 50 to 70% in addition to non-reactive aromatic compounds.

The quantitative ratios of phenols or phenol mixtures to unsaturated, aromatic compounds are between 20:80 to 50:50% by weight.

• 20-40 Gew.-% phenolische Verbindungen
• 78-30 Gew.-% aromatische, ungesättigte Kohlenwasserstoffe und
• 2-30 Gew.-% Isobuten

If these aromatic hydrocarbons are polymerized together with isobutene, which is sometimes appropriate to improve the compatibility with non-polar solvents, the proportions of the reactants are in the following ranges:

• 20-40 wt .-% phenolic compounds
• 78-30% by weight of aromatic, unsaturated hydrocarbons and
• 2-30 wt% isobutene

The amounts of phenolic compounds used ensure that the resulting resins have an OH number of at least 4.5. It is possible to increase the OH number to over 9 by using polyhydric phenols.

The polymerization of these unsaturated compounds is generally carried out using acids or Friedel-Crafts catalysts such. B. trichloroacetic acid, boron trifluoride complexes, aluminum, antimony V or tin IV chloride.

To carry out the polymerization, catalyst and phenol or phenol mixture are introduced. The phenol component should be dissolved. It has been found that it is expedient to use part of the hydrocarbon reaction as solvent and thus to work with a minimum of solvent. When such a solution is used, the polymerization reaction starts immediately and may have to be kept within the temperature limits by cooling. After this first polymerization step, the remaining resin oil fraction is added so that the polymerization continues at a constant temperature.

If the original reaction mixture does not yet contain any unsaturated, aromatic hydrocarbons, these are metered in such a way that the temperature of the reaction mixture first rises to the desired polymerization temperature and that the temperature is kept constant in the further course of the polymerization.

These polymerization temperatures are in the range from 30 to 70 ° C., higher softening points being achieved on the one hand at lower temperatures, but also extending the polymerization time on the other.

In the case of copolymerization with isobutene, the reaction temperature is in the range from 20-140 ° C. It is due to the boiling point of the isobutene and the pressure prevailing during the reaction.

To carry out the polymerization, the catalyst and phenol or phenol mixture are preferably introduced as a solution in aromatic solvents and the unsaturated, aromatic hydrocarbons and the isobutene are gradually metered in in a predetermined ratio. This can be done by cooling the unsaturated, aromatic hydrocarbons and isobutene and keeping it at a temperature below the start of boiling of the mixture and metering this mixture into the phenolic compounds in portions with cooling. Then the reaction can be carried out under normal pressure. But it is also possible to mix the phenolic compounds and the catalyst to add the aromatic, unsaturated hydrocarbons and the isobutene separately without cooling in the predetermined ratio. The gaseous isobutene is pressed into the reaction vessel under a pressure of up to 6 bar and the reaction is carried out under a pressure of up to 4 bar. The neutralization of the catalyst and the further processing of the resin are carried out according to methods known per se.

With optimal polymerization, which is given by a low polymerization temperature and a one to two hour after-reaction at this temperature, stable, phenol-modified hydrocarbon resins with OH numbers of more than 4.5 and softening points up to 65 ° C can be produced with monohydric phenols .

If fully or partially polyhydric phenols such as pyrocatechol or resorcinol are used as phenolic compounds, stable resins with OH numbers up to about 10 are obtained. It has been found that these resins have softening points of 65 to 80 ° C.

The softening points for a developer resin for pressure-sensitive recording materials are limited to a relatively narrow temperature range in that experience has shown that products with a softening point of more than 110 ° C. generally no longer cause color development. Obviously, such resins are not sufficiently dissolved by the solvent of the leuco pigment for a coloring reaction. It follows that a resin with the lowest possible softening point would be desirable for this reaction. On the other hand, the resin must not stick at room temperature and, which is particularly important with paper as the carrier material, it must remain as a layer on the carrier material and must not move into it. Based on these considerations, the softening point should be as high as possible. As a result of these restricting parameters, the softening points of the resins have a still tolerable range of 55 to 110 ° C and a range of 70 to 90 ° C preferred for carbonless papers.

The use of polyhydric phenols in the production of the phenol-modified hydrocarbons according to the invention therefore makes it possible to set the softening points of the resins in the optimum temperature range for carbonless papers and at the same time to at least improve the developer properties.

Another possibility to increase the softening point of the phenol-modified hydrocarbon resins, or to set it almost arbitrarily in the range mentioned, is offered by copolymerization with vinylphenol or a vinylphenol substituted by halogen, alkyl or aralkyl in the core or the alkene chain.

Surprisingly, it has been found that vinylphenols copolymerize with unsaturated, aromatic compounds and phenolic compounds. Due to the extraordinary reactivity of the vinyl phenols, it was to be expected that the relatively inert, unsaturated, aromatic compounds and the non-polymerizing phenols, which would only participate through an alkylation reaction, would not react. However, there is a true copolymerization which gives a uniform resin.

The amounts of vinylphenol are, depending on the desired softening point, between 10 and 30% of the components to be polymerized, with about 10 to 70% of the phenols being replaced by vinylphenol. It would also be possible to replace all of the phenolic compounds with vinylphenols, but this is not desirable for economic reasons and also results in resins with a softening point which is too high.

The polymerization reaction also takes place by isothermal polymerization in such a way that vinylphenol, the phenolic compounds, the unsaturated, aromatic hydrocarbons and optionally isobutene are mixed with one another and a Friedel-Crafts catalyst is added. The polymerization reaction is optionally carried out isothermally with external cooling after reaching the selected polymerization temperature, which is in the range from 30-90 ° C.

After the reaction has ended, the mixture can be heated after 15-30 minutes to complete the polymerization reaction.

The catalyst is then removed by washing or precipitation and filtering, and unpolymerized constituents are removed from the resin by distillation at atmospheric pressure or in vacuo and subsequent steam distillation.

The resins obtained are almost colorless, non-yellowing, odorless products with softening points which, depending on the composition, are in the range of 70-110 ° C. When reacting with a leuco pigment, they result in a color development from OH numbers of just 4.5, which is very good for a pressure-sensitive carbonless paper.

The invention is further illustrated by the following examples. Percentages are percentages by weight. The softening points (E.P.) are determined using the Krämer-Sarnow method. The OH number is determined by acetylation with subsequent saponification to determine the required amount of a known KOH solution.

example 1

By isothermal polymerization at 35 ° C of a batch of 150 g phenol fraction containing 48% phenol and 16% cresols and 36% xylenols, 50 g toluene, 5.4 g BF ₃ methyl etherate, 350 g resin oil fraction with a boiling range of 160 -220 ° C (indene content 63%) a bright, non-yellowing, almost odorless resin with an EP of 55 ° C and an OH number of 6.4 is obtained (yield 73% of the polymerisable components).

Writing exam

10 g of resin are dissolved in 100 ml of toluene (ethyl acetate). This solution is used to moisten one side of a sheet of commercially available typewriter paper and then to evaporate the solvent. The paper prepared in this way corresponds to the copy side of a pressure-sensitive carbonless paper system. It is placed on a cover sheet of a commercially available carbonless paper system which is microencapsulated with one or more leuco pigments and a high-boiling solid organic solvent, so that the two coated sides lie one on top of the other. The copying system thus produced is described in a customary manner with a normal typewriter.

• sehr gut volle Farbentwicklung
• gut die Schrift ist gut lesbar
• ausreichend die Schrift ist nach 10 sec gerade lesbar, die Farbe vertieft sich innerhalb einer Minute
• nicht ausreichend es wird kein lesbares Schriftbild entwickelt.

After 10 seconds, the font development on the carbon sheet is assessed. The assessment is based on the following categories:

• very good full color development
• well the writing is legible
• sufficient the writing is legible after 10 sec, the color deepens within a minute
• not sufficient no legible typeface is developed.

The font development achieved with the developer resin produced is good.

Example 2

Isothermal polymerization at 25 ° C of a batch of 150 g phenol fraction according to Example 1, 50 g toluene, 5.4 g BF ₃ methyl etherate, 320 g resin oil fraction (boiling range 160-220 ° C), 18 g isobutene becomes a light, almost odorless resin with an EP of 60 ° C and an OH number of 5.9.

Writing tests in the same way as in Example 1 result in good writing.

Example 3

A bright, non-yellowing, almost odorless resin is obtained by isothermal polymerization at 40 ° C. of a batch of 3630 g of phenol fraction according to Example 1, 80.6 g of BF ₃ methyl etherate, 3000 g of resin oil fraction / boiling range 160-220 ° C., 1090 g of isobutene obtained with an EP of 60 ° C and an OH number of 5.8.

When writing tests as in Example 1, there is sufficient writing development.

Example 4

Isothermal polymerization at 40 ° C. of a mixture of 75 g phenol, 25 g toluene, 2.7 g BF ₃ ethyl etherate, 80 g divinylbenzene, 100 g resin oil fraction with 53% vinyl toluene content (boiling range 160-172 ° C) gives a bright, obtained non-yellowing almost odorless resin with an EP of 57 ° C and an OH number of 5.8.

When writing tests as in Example 1, there is sufficient writing development.

Example 5

Isothermal polymerization at 60 ° C of a mixture of 40 g resorcinol, 350 g toluene, 3.1 g BF ₃ methyl etherate, 240 g resin oil fraction (boiling range 160-220 ° C) gives a bright, non-yellowing, almost odorless resin with a EP of 67 ° C and an OH number of 9.3 obtained (yield 35% of the polymerizable parts).

Writing tests in the same way as in Example 1 resulted in very good font development.

Example 6

Isothermal polymerization at 60 ° C of a mixture of 40 g pyrocatechol, 280 g toluene, 3.1 g BF ₃ methyl etherate, 240 g resin oil fraction (boiling range 160-220 ° C) gives a bright, non-yellowing, almost odorless resin with a EP of 72 ° C and an OH number of 7.1 obtained (yield 79% of the polymerizable parts).

Writing tests in the same way as in Example 1 result in good writing.

Example 7

Isothermal polymerization at 60 ° C of a mixture of 200 g phenol, 300 g p-vinylphenol, 15 g BFg methyl etherate, 787 g resin oil fraction (boiling range 160-220 ° C) gives a bright, non-yellowing, almost odorless resin with an EP obtained from 80 ° C and an OH number of 4.9.

Writing tests in the same way as in Example 1 resulted in very good font development.

Example 8

Isothermal polymerization at 80 ° C of a batch of 160 g phenol, 220 g p-vinylphenol, 15 g BFg methyl etherate, 976 g resin oil fraction (boiling range 160-220 ° C) gives a bright, non-yellowing, almost odorless resin with an EP obtained from 70 ° C and an OH number of 4.5.

Writing tests in the same way as in Example 1 resulted in very good font development.

Comparative example

A polyvinylphenol resin produced by polymerizing p-vinylphenol with an EP of 185 ° C. and an OH number of 14 shows no developer properties in a written test analogous to Example 1.

Claims (6)

1. A resin for developing of leucopigments in pressure sensitive recording materials which is a stabilized, phenolic-modified hydrocarbon resin with an OH-number of at least 4,5 and a softening point in the range of 55-1.10 °C.

2. The resin as in claim 1, having a softening point in the range of 70 to 90 °C.

3. The resin as in claims 1 and 2, wherein as phenolic compounds multivalent phenols are used wholly or partly.

4. The resin as in the claims 1-3, which is copolymerized with isobutene.

5. The resin as in the claims 1-4, which is copolymerized with vinyl phenol.

6. A process for the production of the resin as in claim 5, comprising mixing vinyl phenol, the phenolic compounds, the unsaturated aromatic hydrocarbons, and, if necessary, the isobutene with one another and treating with a Friedel-Crafts-catalyst, permitting the polymerization reaction to proceed isothermally after reaching the selected polymerization temperature in the range of 30 to 90 °C, optionally with exterior cooling.