EP0801700A1 - Use of optically brightened plastics for optically brightening paper-coating compounds and paper-coating compounds optically brightened in this manner - Google Patents

Abstract

The invention concerns paper-coating compounds which have high brightness, a high greying limit and high light-fastness and can be produced by means of optically brightened fine-particle plastics.

Description

 Use of white-tinted plastics for whitening paper coating slips and such white-tinted paper coating slips

The invention relates to the use of white-tinted, finely divided plastics for

White tones of paper coating slips based on synthetic binders and paper coating slips containing such white tinted plastics.

A large number of aqueous coating slips based on polymeric binders are used to produce coated papers and cardboard boxes. Common binders for paper coating slips include, for example, butadiene / styrene,

Styrene / butyl acrylate, acrylonitrile / butadiene / styrene, styrene / butadiene / acrylic acid alkyl ester, acrylic acid alkyl ester, ethylene-vinyl chloride and ethylene-vinyl acetate copolymers as well as the homopolymers polyethylene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate and polyaddition compounds such as polyurethanes.

In addition to the usual white pigments - especially china clay and calcium carbonate - the coating slips for optical brightening usually contain anionic white tones, e.g. those of the bis-triazinyl-aminostilbene-disulfonic acid type. However, these whiteners only lead to very unsatisfactory white effects and to very low graying limits (= whitener concentration, at which further addition of whites does not result in an increase or even a decrease in the whiteness). In addition, the types of white toner mentioned in the coating slips do not have adequate lightfastness.

It has already been recommended to improve the white effect in coating slips by using hydrophilic cobinder or carrier ("Das Papier" 36 (1982) 66;

DE-OS 3 502 038, EP-A 4 37 90). However, the hydrophilicity of the added components increases the water sensitivity of the coated paper to an undesirable extent.

It has also been proposed to use dispersion brighteners in the presence of dispersants (GB-PS 1 294 173, 1 349 934). However, the whiteness that can be achieved and the strong dependence of whiteness on the drying temperature cannot be satisfactory. Water-soluble white toners have also already been condensed with aminoplasts and these condensates have been particularly recommended for whitening paper coating slips (DE-OS 3 112 435). However, these proposals have not been able to assert themselves due to insufficient lightfastness and rheological difficulties , high graying limit and good light fastness is a difficult task that has not yet been satisfactorily solved

It has now surprisingly been found that white-toned, fine-particle plastics which are not aminoplasts give paper coating slips very high degrees of whiteness, high graying limits and high lightfastness

The invention therefore relates to the use of white-toned, finely divided plastics from the series of polyacrylonitrile, polyamide, polyester, polyolefins, vinyl aromatic polymers and cellulose or cellulose regenerates for whitening paper coating slips based on synthetic binders

The plastics on which the white-toned plastics to be used according to the invention are based include polyacrylonitriles, polyamides, such as, for example, polyamide-6 and polyamide-6 6, and polyesters, in particular those based on phthalic acid, iso- and / or terephthalic acid and ethylene glycol, butanediol-1,4 and / or bis (hydroxymethyl) cyclohexane, polyester based on maleic acid and / or fumaric acid and / or p-phenylenediacetic acid and / or 44'-diphenyldicarboxylic acid and / or 2 6-naphthalenedicarboxylic acid as well as ethylene glycol, polyester based on 4-hydroxybenzoic acid, polyolefins such as polyethylene and polypropylene, vinyl aromatic polymers such as polystyrene, cellulose and regenerated cellulose such as viscose and acetyl cellulose (especially cellulose di- and triacetate)

Preferred polyacrylonitriles have intrinsic viscosities (measured in dimethylformamide at 20 ° C.) of 1.18 to 222 dl / g, preferred polyamides have relative viscosities (measured on a 1% strength by weight solution in m-cresol at 25 ° C. an Ubbelohde viscometer) of 2 to 5.5, preferably 2 to 4, and preferred polyesters have intrinsic viscosities (measured in phenol / tetrachloroethane = 60:40 (parts by weight) at 25 ° C) from 0.4 to 1.5 dl / g.

For the purposes of the invention, “fine particles” are plastic powders with a particle size (determined as weight average) of less than 1 μm.

For the selection of preferred white tones, the person skilled in the art can orientate himself on the optical brighteners which are used for white tones in the textile sector. Preferred whiteners result in comparatively high light fastnesses on textile fibers - measured in the Xenotest based on the guidelines for the determination of color fastnesses according to DIN 54004 - of at least 4, preferably from 5 to 7.

Preferred white toners for finely divided polyacrylonitriles are compounds of the formulas:

wherein R represents ethyl or phenyl;

wherein for CH or N, R ¹ for CH ₃ or CH ₂ -C ₆ H ₅ and

R ² for H or SO ₂ -CH. stand; and wherein

Anion of a mineral acid, formic acid, acetic acid, lactic acid or

-O ₃ SOCH ₃ mean

Preferred white toners for finely divided polyamides are compounds of the formulas

and

 wherein

M represents an alkali metal or hydrogen Preferred white toners for finely divided polyesters are compounds of the formulas

wherein

R ^{4 is} phenyl or a radical of the formula and

R ^{5 is} a radical of the formula

mean;

wherein

R ⁶ and R ⁷ independently of one another are hydrogen, C ₁ -C ₄ alkyl or C ₁ -C ₄ alkoxycarbonyl and

X ¹ for _,,,

 stands;

wherein

R ⁸ and R ⁹ independently of one another are hydrogen or C ₁ -C ₄ -alkyl,

R ^{10 is} C ₁ -C ₄ alkyl, phenyl or C ₁ -C ₄ alkoxycarbonyl and

Represent 0 or 1;

 the CN groups can each be in the o-, p- or m-position and their isomer mixtures; and

wherein

R ^{11 is} C ₁ -C ₄ alkoxy-carbonyl.

Very particularly preferred white-tinted plastics contain white-tinted polyacrylonitrile with white tones of the formulas (1) or (2), white-tinted polyamide with white tones of the formula (5), or white-tinted polyester with white tones of the formulas (6) or (7).

The finely divided, white-tinted plastics can be incorporated into the paper coating slips in powder form. In most cases, however, it should be more convenient to disperse the finely divided plastics in the aqueous phase before or after the application of the white toner and, after the white toner has been applied, if appropriate, to incorporate the aqueous plastic dispersion obtained into the paper coating slips.

These plastic dispersions can A) 1 to 30% by weight, preferably 5 to 25% by weight of the white-tinted polymers, B) 1 to 50% by weight, preferably 5 to 20% by weight of surface-active substances, C) 0 to 15 wt .-% preservative and D) 20 to 98 wt .-%, preferably 55 to 90 wt .-% water, with up to half of the water by hydrotropic substances such as Ethylene glycol or glycerin can be replaced and the percentages relate to the sum of A + B + D. Anionic, cationic and / or non-ionic surface-active substances can be used as surface-active substances, such as are used, for example, in methods of organic chemistry (Houben-Weyl), 4th edition, vol. XIV / I, Georg Thieme Verlag, Stuttgart 1961, P. 190 f. and in DE-OS 2 334 769, pages 8 to 10 (Δ GB-PS 1 417 071) are described. Dispersions of the finely divided, white-tinted plastics to be used according to the invention can be produced, for example, as follows:

The powdered polymers are first treated with the white toners suitable for the selected substrate in aqueous systems at temperatures from 60 ° C. to the boiling temperature until the white toners are completely absorbed onto the substrate. If necessary, additional aids are used. However, the white tones can also be fixed in the melting process on the corresponding polymer materials.

The amount of white toner used on the substrate depends on the desired lightening effect; it is between 0.01 and 5% by weight of pure active substance, based on the plastic used (solid).

The isolated white-tinted plastic powder is then homogenized after the addition of a surface-active substance and, if appropriate, water, with vigorous stirring. The amount of the surface-active substance can then be increased, if necessary to the total amount required for the stability of the dispersion. The suspension obtained is then comminuted and ground wet.

The pre-shredding can be done using stone or tooth colloid mills. The subsequent wet comminution can take place in colloid, vibratory, cone and vibromills as well as in dissolvers or in sub-micron dispersers. However, continuous agitator mills with grinding media, preferably those made of SiO ₂ with a diameter of 0.2 to 5 mm, are preferably used.

After the grinding treatment, further amounts of surface-active substances or hydrotropic substances, preservatives, wetting agents, defoamers and / or water can optionally be added, provided that this has not been done at an early stage, e.g. before grinding, the isolated white-tinted plastic powder can also be incorporated directly into the paper coating slips after dry grinding.

A particularly advantageous way of producing a dispersion of white-tinted plastic is the combination of the whitening process and the grinding process: For this purpose, the powdered plastic together with the corresponding whitener, water and surface-active substances at temperatures from 60 ° C to the cooking temperature, if necessary, after Homogenization and pre-grinding, wet grinding as described above. The complete brightening takes place during the grinding process in the grinder, preferably in a continuous agitator mill with SiO ₂ grinding media. The amount of white toner used in the paper coating slip depends on the desired white effect. In general, 0.01 to 0.5% by weight of pure white toner (based on the solids of the paper coating slip to be lightened) are sufficient. A particular advantage is that, depending on the coating composition, the graying limit that can be achieved is extremely high.

The paper coating slips generally have solids contents of 35 to 80, preferably 40 to 70% by weight. In addition to the white-tinted, fine-particle plastic to be used according to the invention, they generally contain (details based on solids) a) 100 to 150 parts by weight of inorganic pigment,

b) 3 to 25 parts by weight of binder, of which up to half may consist of natural (i.e. non-synthetic) cobinder (such as starch, casein),

c) up to 1 part by weight of thickener and

d) up to 2 parts by weight of wet strength agent.

The percentages in the following examples relate to the weight; Parts are parts by weight.

Examples

Example 1 White-toned polyacrylonitrile

100 g of polyacrylonitrile powder ( ^® Dralon RK, Bayer AG) are suspended in 1 l of demineralized water. The pH is adjusted to 2.5 with formic acid. At 60 ° C., 0.2, 0.5, 1 or 1.5% of white toner is obtained Formula (1) (R = ethyl and An = - SO ₃ OCH ₃ ) is added and the mixture is heated to boiling temperature. The mixture is then stirred at 98 ° C. for 20-40 min. It is suctioned off at 60 ° C. and the pulp, which is toned white, in a vacuum drying cabinet at 40 ° C dried The white-toned powders show the following degrees of whiteness

 Example 2 Dispersion of white-toned polyacrylonitrile

188 of the weißgetonten ld prepared according to Example polyacrylonitrile powder g (1.5% fixed toner white) together with 140 g of dispersant (a ethoxyhertes nonylphenol / cyclohexylamine adduct ^® Avolan ONP 100%, Bayer) and 672 g of water are homogenized with a Dental colloid mill pre-crushed

The suspension is then wet comminuted in a bead mill at room temperature with 4 passes. The resulting stable dispersion is easy to incorporate into paper coating slips and shows excellent white effects with high lightfastness, even with high additions Example 3: Paper coating slip (not according to the invention)

By stirring together

50 parts of China Clay SPS,

50 parts calcium carbonate (chalk),

12 parts of an anionic plastic dispersion of an acrylic acid ester

Copolymers with a solids content of 48% ^(® Acronal S 320 D from BASF),

0.5 parts of polyvinyl alcohol and

80 parts of water is a paper coating slip with a solids content of about 55%, the pH of which is adjusted to 9 with sodium hydroxide solution (coating slip 3).

Example 4:

A) 150 g, b) 300 g and c) 450 g of dispersion according to Example 2 are incorporated into each 1 kg of the coating color according to Example 3. To produce the coated papers, the coating slips 3 and 4 a) -c) are applied to paper with the aid of a hand-held squeegee or an experimental coating system and dried at 80.degree. Table 2 shows the degree of whiteness CIE of the papers after production and after exposure (1 week in daylight).

 Even with a very low white toner concentration, the papers according to the invention show both an increased degree of whiteness and a significantly improved light fastness. In the same way as the dispersions, corresponding amounts of white-toned polyacrylonitrile powder according to Example 1 can also be incorporated directly into this coating slip

Example 5: White-toned polyacrylonitrile

If the procedure is as described in Example 1, instead of the white toner of the formula (1) (R = ethyl and An = -SO ₃ OCH ₃ ), 1% white toner of the formula (2)

(X = CH, R ¹ = methyl, R ² = SO ₂ -CH ₃ and An = -SO ₃ OCH ₃ ) and working up as described, you also get polyacrylonitrile powder suitable for the lightening of paper coating slips (Weissgrad Berger 156 , CIE 147.6), which, in the same way as described in Example 2, gives a stable dispersion which can easily be incorporated into paper coating slips and is excellent there

White effects with high light fastness and high graying limit delivers

Example 6: White-toned polyamide

8 g of sodium dithionite, 12 g of ethoxylated nonylphenol (7-10 mol of ethylene oxide) and xg (see Table 3) of the brightener of the formula (4), (M = K), are suspended in 4 l of demineralized water. The mixture is heated to 80 ° C. and at this temperature 100 g Polyamide powder (polyamide 6D, Riedel de Haen) added in portions. The mixture is then stirred for 30 minutes at the cooking temperature. After cooling to 80 ° C is suctioned off and dried at 40 ° C in a vacuum drying cabinet. White-tinted polyamide powder with the following white values is obtained.

 Example 7; Dispersion of white tinted polyamide

In a laboratory agitator mill filled with 290% glass beads (0.4-0.52 mm in diameter), 25% of the polyamide powder (2% fixed brightener), which is tinted white according to Example 6c, 20% emulsifier (an ethoxylated biphenyl, emulsifier W from Bayer) ) and 55% water at room temperature and 1 700 rpm for 90 min. The resulting stable dispersion can easily be incorporated into the paper coating slip in the present form.

Example 8: Paper coating slips

Coating slips and paper coatings can be produced in the same way as described in Example 4. Instead of the pigment dispersion from Example 2, the corresponding amount of a pigment dispersion according to Example 7 is used. Table 4 shows the degree of whiteness CEE of the papers after production and after exposure (1 week in daylight).

 Example 9: White tinted polyamide

100 g of polyamide powder as in Example 6, 8 g of sodium dithionite, 12 g of ethoxylated nonylphenol (7-10 mol of ethylene oxide) and 1 g of the brightener of the formula (5) (M = Na) are suspended in 4 l of demineralized water. It is heated to the boiling temperature and stirred at this temperature for 30 min. After cooling to room temperature, the product is filtered off with suction and dried at 40 ° C. in a vacuum drying cabinet. The white tinted polyamide powder shows whiteness Berger of 154.3 and CIE of 146. Example 10: Dispersion of white tinted polyamide

25% of the white-tinted polyamide powder (1% of fixed brightener), 20% of emulsifier and 55% of water at room temperature are dispersed as described in Example 7. The resulting stable dispersion can be incorporated directly into the paper coating slip. Excellent lightening effects with high light fastness and bleeding fastness are obtained.

Example 11: White tinted polyester

100 ml of polyester powder (polyethylene terephthalate, Agfa), 1 g of an anionic dispersing agent ( ^® Avolan IS, Bayer), 2 g of auxiliary agent (Levegal PEW, Bayer) and 1 g of the whitener of the formula (7) (R ⁶ =

R ⁷ = CH ₃ , and X ¹ : -CH = CH-) suspended. It is heated to the boiling temperature and stirred at this temperature for 60 min. After cooling to room temperature, the product is filtered off with suction and dried at 40 ° C. in a vacuum drying cabinet. The white-tinted polyester powder has a Berger whiteness of 147.3. Example 12: Dispersion of white tinted polyester

In a laboratory agitator mill filled with 290% glass beads (0.4-0.52 mm in diameter), 25% of the polyester powder (1% fixed brightener) tinted white according to Example 11, 20% emulsifier (an ethoxylated biphenyl, emulsifier W from Bayer) ) and 55% water at room temperature and 1700 rpm for 90 min. The resulting stable dispersion shows excellent white effects with high light fastness and very good fastness to bleeding after incorporation into paper coating slips.

Example 13: White-tinted polyester dispersion

If the procedure is as described in Example 11, instead of 1% of the white toner of the formula (7) (R ⁶ = R ⁷ = CH ₃ , and X ^{1 =} -CH = CH-), 1% of the white toner of the formula (6) is added

 and works as described in Example 1 1, this also gives a polyester powder which is suitable for lightening paper coating slips and which, in the same way as described in Example 12, gives a stable pigment dispersion which can easily be incorporated into paper coating slips and there delivers excellent white effects with very high light fastness, high bleeding fastness and high graying limit.

Claims

Claims Use of white-tinted, finely divided plastics from the series of polyacrylonitrile, polyamide, polyester, polyolefins, vinyl aromatic polymers and cellulose or cellulose regenerates for whitening paper coating slips based on synthetic binders. Use of white-tinted, finely divided polyacrylonitriles as claimed in claim 1, the whitener being one of the series consisting of  wherein R represents ethyl or phenyl,  wherein X for CH or N, R ¹ for CH, or CH, -C ₆ H ₅ and R ^{2 is} H or SO ₂ -CH ₃ ; and  wherein R ³ for NH ₂ , CH ₃ , NH-C ₃ H ₆ -N (CH ₃ ) ₃ ⁺ An, C ₂ H ₄ -N (CH ₃ ) ₃ ⁺ An, CH ₂ -CH (CH ₃ ) -N (CH ₃ ) ₃ ⁺ An, CH (CH ₃ ) -CH ₂ -N (CH ₃ ) ₃ ⁺ An, C ₂ H ₄ -O-CH (CH ₃ ) -CH ₂ -N (CH ₃ ) ₃ ⁺ an or C ₂ H ₄ -CO-NH-C ₃ H ₆ - N (CH ₃ ) ₃ ⁺ arrival and Anion of a mineral acid, formic acid, acetic acid, lactic acid or -O ₃ SOCH ₃ mean  is selected. Use of white-tinted fine-particle polyamides according to claim 1, wherein the whitener from the series consisting of  and  M represents an alkali metal or hydrogen. Use of white-tinted fine-particle polyester according to claim 1, wherein the whitener from the series consisting of  wherein R ^{4 is} phenyl or a radical of the formula and R ^{5 is} a radical of the formula or  mean;  wherein R ⁶ and R ⁷ independently of one another are hydrogen, C ₁ -C ₄ alkyl or C ₁ -C ₄ alkoxycarbonyl and X ¹ for ,,, - or stands;  wherein R ⁸ and R ⁹ independently of one another are hydrogen or C ₁ -C ₄ -alkyl, R ^{10 is} C ₁ -C ₄ alkyl, phenyl or C ₁ -C ₄ alkoxycarbonyl and n is 0 or 1; and  wherein R ¹¹ denotes C ₁ -C ₄ alkoxycarbonyl, is selected. 5. Use according to claims 1-4, according to which the white-tinted polymer powders have been subjected to wet comminution in the presence of surface-active substances. 6. Use according to claims 1-4, according to which the finely divided plastics have been wet-ground together with the whiteners and water and surface-active substances at temperatures from 60 ° C. to the cooking temperature, if appropriate after homogenization and pre-comminution, during the grinding process in the grinding apparatus. 7. With the help of the white-tinted plastics according to claims 1-6 white-tinted paper coating slips based on synthetic binders.