EP0695236A1

EP0695236A1 - Pressure-sensitive self-copying paper with improved oil barrier

Info

Publication number: EP0695236A1
Application number: EP94914390A
Authority: EP
Inventors: Bodo Hilterhaus; Dieter Baumgarten; Guenter Gabel; Wolfram Friesen
Original assignee: Stora Feldmuehle AG
Current assignee: Stora Publication Paper AG
Priority date: 1993-04-21
Filing date: 1994-04-16
Publication date: 1996-02-07
Anticipated expiration: 2014-04-16
Also published as: ES2105702T3; EP0695236B1; DE59403256D1; WO1994023952A1; CZ274795A3; DE4312854A1

Abstract

A layer containing microcapsules with leuco dyes dissolved in kernel oil is placed on the lower face of pressure-sensitive recording paper. In order to prevent the kernel oil from diffusing through the carrier paper, the carrier paper contains an oil barrier with an oil adsorption value lower than 10 g/m2, measured using the Cobb-Unger method, and the hot water extract has a pH value from 7.5 to 9.5. The oil barrier consists of an impregnation worked into the mass of the carrier paper or an oil-repellant surface preparation of film-forming hydrocolloids, plastic dispersions, pigments or mixtures thereof applied on one or both sides of the paper.

Description

Pressure sensitive carbonless paper with improved oil barrier

The invention relates to a pressure-sensitive carbonless paper according to the preamble of claim 1.

Pressure-sensitive carbonless papers based on the chemical reaction principle consist of a backing paper and reaction layers applied to it and are referred to as CB, CFB and CF papers according to the current nomenclature. CB means a copy sheet with microcapsules arranged on the back, CFB a copy sheet with color developer layer arranged on the top and a microcapsule layer on the back, CF a copy sheet with color developer layer arranged on the top. The principle of the reaction is that the microcapsules arranged on the back break up as a result of the writing pressure applied to the paper and their contents, leuco dyes dissolved in so-called core oil, are transferred to an underlying receiver layer of the following copy sheet, whereby Due to its chemical composition, the receiving layer develops the leuco dye into a visible color, so that the writing trace is readable by the human eye. Such papers are well known so that they do not have to be described further.

For the intended use, carbonless sheets of this type are compiled into so-called carbonless records, which in the simplest case consist of a CB and a CF sheet for the purpose of producing an original and a copy or copy. However, if several copies are to be created, the individual sheet types must be arranged in the following order: CB-CFB ... CFB-CF.

Form sets from pressure sensitive

Carbonless papers must be printed, although it cannot always be avoided that individual capsules are destroyed during the printing process and their contents are released onto the carrier paper. If its resistance to core oil penetration is too low, the leuco dyes contained in the core oil react with the color developer located on the top of the carrier sheet, so that the carbonless paper or the set of forms made from it shows a discolouring discoloration even before it is actually used. In the past, it has been shown in particular that yellow and red color precursors tend to migrate through the carrier paper in the event of premature capsule destruction. As a result, copies of important documents that were kept in the file turned strongly yellow or red over time, so that their document character is ultimately endangered.

Experiments carried out by the applicant several years ago with regard to improving the mass sizing of the base paper showed that this undesired migration of dyestuffs can only be avoided by conventional acidic resin sizing.

The disadvantages of acidic resin sizing with regard to the resistance of such papers are now well known: As a result of hydrolysis reactions of the aluminum sulfate used, long-term destruction by acid corrosion occurs, with the result that the document is destroyed.

Another disadvantage of acidic resin sizing is the incompatibility of the use of calcium carbonate pigments as a filler in the base paper or as an extender pigment in the color developer layer. However, because of its high whiteness and value for money, the use of this pigment is a mandatory prerequisite for the economical production of pressure-sensitive carbonless papers, as the expert in the field of coated and specially coated papers now knows. Although the production of neutral sized printing and writing papers also for the use of tabulating and office papers using calcium carbonate as a filler and so-called AKD glues (alkyl ketene dimer compounds) to achieve sufficient ink writability for the paper technician meanwhile State of the art, this sizing process could not prevail at all in the production of pressure-sensitive carbonless papers because of the lack of a blocking effect against the migration of leuco dyes dissolved in core oil. This was all the more surprising since all common test methods for the degree of sizing of the backing papers showed no deviation in the results from those of acid-sized backing papers.

In patent application P 36 33 116, which goes back to the applicant, a pressure-sensitive carbonless paper is proposed, the microcapsule of which contains a vegetative oil such as e.g. Sunflower oil, rapeseed oil, soybean oil, coconut oil etc. as an environmentally friendly core oil as a solvent for the color precursor or known leuco dyes.

During the practical testing of such carbonless papers, however, it had to be found that these core solvents had adverse effects when used as intended. Due to their composition, they led to a so-called grease stain effect, ie they led to an undesired opacification and a subsequent widening of the original trace. This detrimental appearance could neither be avoided by the known acid resin sizing nor by the more recent alkaline sizing of the backing paper. Even common surface treatments of the carrier paper have not been able to remedy this disadvantage.

Non-reactive water repellents, such as wax glues, wax emulsions, metal salts of fatty acids, such as. B. stearic acid, ester waxes, oxidized polyethylenes, copolymer dispersions and dispersions from organic prepolymers are known per se and have so far been used in paper technology mainly in combination with gelatinized starch in glue liquors for use in the size press within the paper machine, see. also the literature reference "Handbuch der Papier- und Pappefabrikation", 1971, page 1282 ff. under the heading surface sizing with further references. Such substances are also thought to have a blocking effect against oils and fats.

The object of the present invention is therefore to provide a pressure-sensitive carbonless paper which avoids the disadvantages described above and in particular has a better barrier effect against the currently known and proposed core oils of microcapsules.

Core oils are understood to mean all currently known solvents and their mixtures with blending agents, in particular the organic paraffin derivatives, benzene derivatives, Chlorinated hydrocarbons, white oils and vegetative oils are meant, which are known and familiar to the person skilled in the art.

The solution to the problem is given by the characterizing part of claim 1 and the subclaims referring to it, in particular by a pressure-sensitive carbonless paper, the backing paper of which has an oil barrier with an oil adsorption value, measured according to Cobb-Unger in accordance with DIN 53 132 of <10 g / m ² and a pH value of the hot water extract, measured according to DIN 53 124, of 7.5 to 9.5.

The oil barrier according to the invention preferably consists of an impregnation incorporated into the mass of the backing paper. This is obtained in a manner known per se in the production of the backing paper by adding the impregnation substances to the aqueous fiber suspension before the sheet is formed on the paper machine screen. After intensive mixing with the fiber suspension, possibly with the aid of retention agents known per se, such as cationic polyethyleneimines or cationic polyacrylamides, the sheet is formed on the paper machine screen, which contains the impregnating substance which forms the oil barrier according to the invention evenly distributed over its cross section. If the impregnating substance or the mixture of such substances has a charge or an ionic character, this can be used for the retention of the substance in the fiber structure Increasing the oil barrier effect can be used. With a cationic charge of the impregnation substance, the anionic charge of the cellulose fiber is sufficient to obtain sufficient retention. However, if the impregnation substance is anionically charged, it is advisable to precipitate onto the fiber by adding cationic substances such as the retention agents mentioned above.

A further possibility for increasing the retention of the impregnation substance consists in pre-flocking it with oppositely charged polymers and only then adding it to the fiber suspension. Finally, it is already known to the person skilled in the paper manufacture to use anionic or uncharged substances with the aid of

Reload cationization reagents to increase their affinity for the pulp fiber. Such cationization reagents are known under the generic term quaternary ammonium compounds. Another representative is the now well-known polydadmac (polydimethyldiallylammonium chloride), dimethyldistearylammonium chloride and benzidimethylstearyl monium chloride.

In certain circumstances, it may be advisable not to add the impregnation substance to the fiber suspension when producing the base paper. This is especially the case if the paper machine has a limited drainage capacity or if the fiber suspension used is already a bad one Has drainage behavior. The addition of the impregnating substance would then further deteriorate the drainage, so that the

Paper machine speed with the consequence of reduced production must be reduced.

To avoid this disadvantage, a further embodiment of the invention provides that the oil barrier consists of an oil-repellent, closed surface preparation applied to one or both sides of the carrier paper. Such a preparation can be applied in a manner known per se within the paper machine using conventional application devices such as a size press or coating device. An aqueous solution or suspension is produced from the constituents of the impregnating substance and, with the help of roller or nozzle application, a uniform aqueous film is produced on the surface of the backing paper, which results in the desired surface preparation after drying. A device known under the name "Speedεizer" is particularly suitable for applying the solution or aqueous suspension.

The oil barrier preferably consists of natural or synthetic hydrocolloids or their derivatives with a high film-forming property. Sodium salts of alginic acid, starch and starch ethers and esters, cellulose ethers such as carboxymethyl cellulose, derivatives of guar, gum arabic, xanthan derivatives, chitosan, purified inhibicelluloses and their derivatives, as well as partial and highly saponified polyvinyl alcohol. These substances can be used individually or in a mixture. Pretreatment of these hydrocolloids with quaternary ammonium compounds such as polydimethyldially, dimethyldistearyl or benzyldimethylstearyl ammonium chloride, where appropriate, will result in an increase in the oil barrier.

Further preferred substances with a high film-forming property for the oil barrier are copolymers, mixed or terpolymers of acrylates, methacrylates, styrene, butadiene, styrene-butadiene, acrylonitrile, polyisocyanate or polyurethane compounds. These substances are available as aqueous plastic dispersions and are e.g. sold under the trade names Basoplaεt, Baysynthol, Isovin or Cyclopal KE.

The polyisocyanates are described, for example, in DE-A-42 11 480 and DE-A-42 26 110.

The oil barrier very particularly preferably consists of a mixture of natural or synthetic hydrocolloids or their derivatives and plastics based on acrylic acid, methacrylic acid, polycarbonates, butadiene-styrene copolymers, butadiene-styrene-acrylonitrile terpolymers and / or polyurethanes or polyisocyanates. Such a combination combines the good film-forming properties of the hydrocolloids with those of the plastics in order to achieve a particularly high barrier action against the core oils. Another advantage is that the - lo ¬

The surface film formed has a certain elasticity and softness due to the proportion of plastic, which can be important for the later use of the pressure-sensitive carbonless paper, this applies in particular to the endless form area, where excessive stiffness is undesirable because of the poorer machinability associated with it.

Another preferred composition of the oil barrier consists of a symplex of cationic starch and anionic alginate. The reaction product from the two constituents is understood to be symplex if they are combined in an aqueous solution in such a way that a complete charge equalization takes place and the original colloids as coacervates or coprecipitates have failed as microflakes. Such coacervates are particularly suitable for addition in bulk, but use for producing a surface film is not excluded.

Fluorinated hydrocarbon compounds with excellent properties have been known for a long time for the production of oil and grease repellent equipment in textiles and special papers for food packaging. Such compounds are available, for example, under the trade name "Scotchban". However, their use has so far been limited to a few special products because of the high cost price. It has now surprisingly been found that an oil barrier with outstanding properties can be made available for pressure-sensitive carbonless papers if this consists of a mixture of polyvinyl alcohol with a degree of saponification of 84-98% and a fluorinated hydrocarbon compound. The mixing ratio of polyvinyl alcohol to fluorinated hydrocarbon compound is selected in the range from 11: 1 to 9: 3. Such a mixture is particularly suitable for producing oil-repellent surface films with the aid of a glue press or a coating unit within the paper machine, the surface application per side being selected between 0.5 to 2 g / m ² atro.

Another solution to the problem is finally to arrange an oil barrier made of olephobic pigments in or above the backing paper. When arranged within the backing paper, these pigments are added in an amount of 10 to 15%, based on dry fiber, as filler of the fiber suspension before the sheet is formed. If the oil barrier is to be arranged as a surface coating, it is sufficient to mix the glue liquor with these pigments in an existing size press and to apply it in an amount of 3 to 5 g / m ² , the liquor being 5-20% atro pigment in addition to the usual surface sizing - and binders. Such an oil barrier can be obtained in accordance with DE-C-30 36 551, which goes back to the applicant. It uses film-forming clays based on montmorillonite achieved a fiber coating that has an excellent barrier effect against the core oils.

The film-forming clays are activated alkaline and contain up to 40% magnesium ions, the rest being sodium ions. Such clays are produced as follows:

In an 8% predispersed

Calcium bentonite suspension, 1.5 wt.% NaOH and 7 wt.% MgS0 _{4 are} added. There is a high viscosity, which is a sign of good activation. A polyethylene glycol with a molecular weight of 20,000 is added from a 6% solution, and the amount added is 18% by weight, based on atro-activated bentonite.

For the production of the oil barrier in the mass, a fiber suspension at pH 7 1 to 3% by weight of the mixture is activated bentonite and

Polyethylene glycol added and with the addition of a known alkali sizing agent such as. B. AKD glue, processed on the paper machine to a carrier paper for pressure-sensitive carbonless papers.

However, it is also possible to use bentonite activated in this way, if necessary with the aid of an additional binder, such as starch, modified starch, latex binder or other binder known to the person skilled in the art, as a surface preparation by means of a size press or a coating device apply alkaline sized paper.

In addition to the activated bentonites, coacervates made from organic pigment and a high molecular weight polymer according to DE-A-40 15 252 or organophilic layered silicates according to DE-A-41 37 091 have also proven their worth, with the purpose of maintaining the oil barrier both in the bulk of the carrier paper incorporated as well as can be applied as a surface preparation. The following examples serve to further clarify:

Composition of the backing paper:

A mixture of 61.7% ground leaf pulp, 26.4% ground needle pulp, 6.8% ground CaC03 filler and 3.1% alkyl-ketene-your-glue, all information related to atro dye, is made on the paper machine at a pH of 7.5 to 8.5, a backing paper with a surface area of 41.5 g / m ^{2 is} produced. The paper has a degree of sizing according to DIN 53 132 from 12 to 18.

The paper is provided with an oil barrier by adding it to the mass or by preparing the surface. The effect of the oil barrier is determined according to the Cobb-Unger method analogous to DIN 53 132 by measuring the absorption of olive oil. An additional evaluation is carried out by the climate aging test on the test sample, a CFB paper being produced therefrom, this aging at 70 ° C. F. is subjected to for 6 days and then through the dye migration caused discoloration of the surface (F side) of the CFB sheet is assessed.

The tests are summarized in Table 1 for the mass impregnation and in Table 2 for the surface impregnation.

Table 1

Trial addition composition impregnation I so-called addition amount, surface Cobb un-migration number location. on atro order quantity test DIN-53 1 32 test backing paper g / m g / m

Zero backing paper, alkaline sized 1.5 g / m '17 probe_

1 mass of Na alginate 2.5% 8.6 +

2 mass of carboxylmethyl cellulose 2.5% 9.2 +

3 mass cat. Guar 2.5% 8.1 +

4 mass of xanthan gum according to EP-A-0 399755 2.5% 9.2 +

5 mass cat. Polyvinyl alcohol 1.0% 9.8 +

6 mass of Symplex Na alginate cat. Strength 1: 1 2, .0% 9.0 +

7 mass Symplex carboxylmethyl cellulose - 2.0% 9.0 +

8 mass of alkaline activated bentonite 1.5% 9.6 +

9 Dimensions according to DE-C-30 36 551

Coacervate according to DE-A-40 15 252 5.0% 9.2 +

0 Mass Modified starch according to DE-A-33 10 088; 22.5% 9.9 +

1 mass cat. Plastic dispersion according to 2.0% 9.5 + EP-A-0 416 427

Table 2

Trial addition composition impregnation Isg addition amount, surface Cobb-Unger migration no. on atro order quantity test DIN-53 132 test

Backing paper g / m g / m

12 Ober¬ latex resin glue combination surface according to DE-A-30 12 821 2.5 g / m '++

13 Surface sizing composition with xanthan-alginate-PVA-CMC starch according to EP 0 399 755 A1 3.0 g / m '3.7 +++

14 Upper styrene acrylic dispersion Baysynthol area ANF (Bayer AG) 3.0 g / m '8.1 ++

15 Ober¬ polyvinyl alcohol 26/88 "Mowiol" area Hoechst 1.5 g / m ² 3.6 + +

16 Ober¬ polyvinyl alcohol 28/99 "Mowiol" area Hoechst 1.5 g / m '3.8

17 Ober¬ polyvinyl alcohol 26/88 + fluorinated surface KW compound Scotchban Fe 807, mixture 10: 2 1.5 g / m ² 3 +++

18 Ober¬ PVAL 28/99 + Scotchban Fe 807 10: 2 1.5 g / m ² 0.8 +++ area

19 Ober¬ PVAL "Airvol 523" (Airproducts, area Utrecht / NL + CMC "Tylose" (Hoechst) 1.5 g / m ² 4.3

20 surface

Table 2

Trial addition composition impregnation Isg addition amount, surface Cobb-Unger migration no. on atro order quantity test DIN 53 132 test backing paper g / m g / m

21 upper alginate solution 1.5 g / m '4.2 area

22 Upper 3% alginate + 50% styrene-acrylate surface dispersion "Baysynthol ANF" (Bayer AG) 1.5 g / m '4.2

23 Ober¬ mixture of 4.85 parts of surface fT-oxyethyl cellulose, 4.85 parts of glycerol, 1.94 parts of glyoxal and 988.5 parts of water 1.5 g / m '4.3

24 top mixture of 3% CMC + 50% styrene surface, acrylic dispersion "Baysynthol ANF" 1.5 g / ι 4.7 + 25 top organophilic sheet silicate according to DE-A-41 37091 1.5 g / m ² 5.7 ++ larp

26> comparison test area

Procote 5000, chemically modified 1.5 g / m '16.1 soy protein according to EP-A-0 491 487

Explanation: unusable: - bad: moderate migration: + minor migration: ++ no migration: +++

Claims

1. Pressure-sensitive recording paper, in which a layer containing microcapsules with leuco dyes dissolved in seed oil is arranged on the underside, the backing paper being glued in bulk, characterized in that the backing paper has an oil barrier with an oil adsorption value, measured according to Cobb-Unger, according to DIN 53 132 of <10 g / m ² and a pH value of the hot water extract of 7.5 to 9.5.

2. Pressure-sensitive carbonless paper according to claim 1, characterized in that the oil barrier consists of an oil-repellent impregnation incorporated into the mass of the carrier paper.

3. Pressure-sensitive carbonless paper according to claim 1, characterized in that the oil barrier from an oil-repellent applied to one or both sides of the carrier paper

Surface preparation exists.

4. Pressure-sensitive carbonless paper according to one of claims 1 to 3, characterized in that the oil barrier from film-forming hydrocolloids such as sodium salts of alginic acid or its derivatives, starch, starch derivatives, cellulose derivatives, guar derivatives, gum arabic, xanthan derivatives, polyvinyl alcohol, hemicellulose, individually or in a mixture consists of it.

5. Pressure-sensitive carbonless paper according to claim 4, characterized in that the hydrocolloids with quaternary

Ammonium compounds such as polydimethyldially, dimethyldistearyl or benzyldimethylstearyl ammonium chloride are pretreated.

6. Pressure-sensitive carbonless paper according to one of claims 1 to 3, characterized in that the oil barrier from copolymers, copolymers or terpolymers of acrylic acid ester, methacrylic acid ester, styrene, butadiene, styrene-butadiene, acrylonitrile, polyisocyanate or Polyurethane compounds exist.

7. Pressure-sensitive carbonless paper according to one of claims 1 to 3, characterized in that the oil barrier from a mixture of hydrocolloids or their derivatives and plastics based on co- or copolymers of acrylic esters, methacrylic acid esters, polycarbonates, butadiene-styrene-col polymers, acrylonitrile-styrene -Butadiene copolymers and / or polyurethanes.

8. Pressure-sensitive carbonless paper according to one of claims 1 to 3, characterized in that the oil barrier consists of a symplex of cationic starch and anionic alginate and / or cellulose ether.

9. Pressure-sensitive carbonless paper according to one of claims 1 to 3, characterized in that the oil barrier consists of a mixture of polyvinyl alcohol with a degree of saponification of 84 to 98% and a fluorinated hydrocarbon compound.

10. Pressure-sensitive carbonless paper according to one of claims 1 to 3, characterized in that the oil barrier consists of pigments.