LU83604A1 - NEW COATING COMPOSITIONS FOR CELLULOSIC MATERIALS - Google Patents

Description

. * · ·.

In order to improve the surface appearance of paper or cardboard and especially their printability characteristics, the paper manufacturer frequently performs the so-called coating operation. The technique consists, by means of an appropriate device, of depositing on one or both sides of the paper or cardboard a layer consisting of one or more pigments and one or more binders as well as in a smaller quantity, of a number of auxiliary products.

Among the pigments most used in coating, 10 of paper, we find very far ahead kaolin and natural or precipitated calcium carbonate. Next come, but in much lower proportions, satin white (calcium sulfo-alurainate), fixed white (barium sulfate), titanium oxide, alumina hydrate, calcium sulfate dihydrate. , the lithopone ..

The diaper bath presents this as an aqueous suspension, with a dry matter content * generally between -20 and 60 in which the pigments represent 70 to 95% of the dry materials, the binders from 4 to 28% the rest 20 being made up of auxiliary products. * -

Schematically we can say that the pigment of the. The layer more specifically conditions the optical and printability properties of the paper, the binder serving to ensure the adhesion of the pigment particles to. the paper and their cohesion 25 ".between them, · while having a predominant action on the" rheology of the diaper bath. It is quite obvious that the nature of the pigment has repercussions on the bond of the layer with the support and that the binder also acts on the properties of primability of coated papers and cardboards.

It has hitherto been considered that it was not possible to incorporate zeolites into the diaper bath because of the thickening which they caused.

• However, it has been found against all expectations, in the departments of the plaintiff, that this drawback is not apparent · · _ _ _ _____ _. "# ·. · I * I · 2. A subject of the present invention is therefore the use, for the preparation of coating compositions, of zeolites of general formula:

Na20, A1203, 2 Si02, * (I) * 5 in which x can vary from 1 to 8, more particularly from. 4 to 5.

These zeolites which can be used as coating pigments can be incorporated into the coating bath in high proportion (for example, up to loo% of the pigment) without causing rheological disturbance. Their presence leads to an improvement in certain important properties of coated paper and cardboard.

The following examples, given without limitation, illustrate the advantages provided by these pigments.

15 'EXAMPLE 1 .. A sodium silico-aluminate of formula • · (I) containing 20% water is used, the average characteristics of which are as follows: .....

. ,; Specific surface 900 - 1100 m2 / g 20 · · Average particle size 2 to 4 μ. · Whiteness (ELREPHO) 95 minimum • Refractive index 1.5 to 1.55 • Density 1.9 to 2.1 g / cm3 • Loss on ignition at 800 ° C 19 to 21% 25. The particles are slightly cubic in shape.

The following aqueous dispersion is prepared: Zeolite X 65 parts dry. Water t 35 parts' · Na hexametaphosphate s 0.25% dry / zeolite '30 · Na polyacrylate; 0.20% dry / zeolite

Dispersion in water is carried out with vigorous stirring as with any other traditional pigment. We obtain an aqueous suspension at about 65% of M.S. and a viscosity of 116 cps measured with the BROOKFIELD viscometer at 50 rpm.

EXAMPLE 2

The zeolite defined in Example 1 is incorporated into a layer bath intended to coat a paper which is to receive offset printing. A reference bath containing only kaolin is prepared simultaneously. In the following baths, 10, 20 and 30 parts of kaolin are substituted for 1 * zeolite equivalent. '10 Layer bath formula - Pigment (English kaolin and zeolite): ICO parts - Na hexametaphosphate dispersant: 0.25 polyacrylate part of Na t 0.2 part ·· Oxidized starch · s 5 parts in dry state 15 - Styrene-butadiene carboxylic latex: 8 parts in dry state • Melanin formaldehyde resin t 0.8 parts in the state - Dry matter; 62% - Starch is broken up in water at 95 ° C at 35% dry matter.

20 a) Bath viscosity · *

The viscosities of the four baths prepared gave the following results: TABLE 1 VISCOSITY BROOKFIELD AT 50 rpm (cps) 25 Quantity Duration of storage kaolin / zeolite __O_ 2 H - 100 / O 1160 1280 90/10 1000 960 30 80/20 580 540 / 70/30 860 840 "/ m 4 4"

The presence of zeolite therefore clearly tends to lower the viscosity of the coating bath. This is a non-negligible advantage because it can result in the possibility of increasing the dry matter content of the baths 5 while retaining acceptable viscosities.

a b) Properties of coated papers

The baths were applied using a threaded rod on an AFNOR VII type support paper (100% bleached chemical pulp). The coated papers were air dried and then conditioned for 24 hours at 23 ° C and $ 50 3 relative humidity. They were then calendered on a super calender with 4 nips, at 80 ° C and under a pressure of 140 kg / linear cm. The papers were then returned to the conditioned room.

1 - Whiteness and opacity of the papers 15 The whiteness was measured using the ELREPHO device with a filter 8 (bandwidth centered on 457 nm) $ the opacity is the printing opacity (paper background) measured with the tris-timulus filter green,

TABLE II

20 KAOlS / ^ OLIXHB WHITENESS "ER OPACITY%. 100 / O 78 94.5 ..

90/10 79.1 ‘94.4 80/20 79.2 94.3 25 70/30 79.4 94.1" "The increase in the zeolite content causes an increase in whiteness. This result is in agreement with the intrinsic high whiteness of the pigment. The opacity is little /, influenced by the zeolite.

• «m 5 2 - Brilliant

The specular reflection of the papers was measured at 45 ° incidence using a gloss meter.

TABLE III

5 QUANTITY SPECULAR REFLECTION

KAOLIN / ZEOLITHE 'A 45 ° 100 / O 30.2 90/10 23 80/20 18.2 10 70/30 15.4

The presence of zeolite very significantly lowers the gloss of the papers. This can result in a valuable advantage for matt coated papers. In fact, in order to obtain matt coatings with the traditional kaolin pigments and, to a lesser extent, CaCo 3, it is necessary to practice very moderate calendering of the papers. This results in a poorer surface condition of the coated papers. With the zeolite the paper can therefore be subjected to vigorous calendering without becoming too shiny.

20 3 - Lissê ^ ... * Measured on BEKK device and expressed in seconds.

TABLE IV ·

SMOOTH QUANTITY BEKK

KAOLIN / ZEOLITHE t in seconds 25 100 / O ·. '1500 90/10 930 80/20 1780 70/30 1630 i. ··. ·. · '’I i 6

The presence of the zeolite promotes a smooth hsut, that is to say a good surface condition of the papers. The loss of gloss observed above is therefore not due to a loss of smoothness, which can be very favorable in the case of the 5 matt coated papers.

4 - Resistance to dry and wet lifting

The pull-out resistance is measured with the I.G.T. under a pressure of 40 kg / cm ^ using graduated inks from Etablissements LORILLEUX.

10 For dry stripping, ink 3806 is used *, (free fall of the pendulum). The results are expressed in mm of length of layer not torn off.

For wet stripping (evaluation of the layer resistance in offset printing), the measurement is at a constant falling speed of the pendulum with the inks 3801 to 3808. The results are expressed according to conventional figures; the better the number, the better.

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TABLE V

Quantity Weight of Water resistance Water resistance 20 Kaolin / INK layer dry chage wet chage zeolite g / m2 Length not pulled out in ran. Value

Peeling inks i - i * 100/0 16.2 60 3,80110 ‘25 90/10 15.6 87 11.6 3,806 to! 80/20 13.8 143 11.7 70/30 15.6 156 3,808 11.9 h. . ·. , / t 7

The resistance of the papers to dry and wet lifting increases with the amount of zeolite in the coating bath. In other words, the demand for binder of zeolite is appreciably lower than that of kaolin, that is to say that in a layer containing zeolite, in order to obtain a determined tear resistance, less binder will be required than for a similar layer containing only kaolin. This results in an obvious economic advantage.

5 - IP II porometric test gives an overall indication of the ink permeability of the papers. The coated papers are brought into contact with the porometric ink for increasing time intervals. The residual reflectance of ink stains on the paper is measured at the ELREPHO device. The results are expressed in% loss of whiteness.

TABLE VI

QUANTITY LOSS OF WHITENESS ELREPHO% KAOLIN / ZEOLITHE Ink-paper contact time 10 s 30 s. 90 s 300 s 20. 100 /. 0 28.6 32.2 38.5 51.0 *. 90/10 29.0 31.1 38.7 49.2 80/20 30.2 33.5 40.2 50.5 70/30 31.6 34.2 40.8 59.9 - »« MM · - \ -_____

The overall porosity of the layer increases slightly with the amount of zeolite.

• ·. ** 6 - Printing with a screened wheel. - / Made on the I.G.T. this test, which gives a. ♦. · M \ m 4; * *.

8 appear no significant difference between the papers. He confirmed that the decrease in calendering gloss was not due to a lower surface finish of the papers containing the zeolite.

i 5 EXAMPLE 3

Layer bath for paper intended to be printed in gravure printing and containing * a synthetic binder as the only adhesive.

- Pigment (English kaolin and zeolite s 100 parts 10 of 1 * example 1) '- Dispersant; Na hexametaphosphate: 0.25 ”Na polyacrylate 0.20” - Acrylic latex * 8 parts dry - Ammonium stearate -fl dry part 15 - Carboxymethyl cellulose t 2 dry parts - NaOH 400 g / 1 q.s. pH 9 - M.S. 62% a) Viscosity of the baths: measured with a viscometer. BROOKFIELD at 50 rpm

20 TABLE VII

; QUANTITY DURATION OF STORAGE

KAOLIN / ZEOLITKE Q H 5 H

100 / O 1360 1040 - 25 90/10 1120 980 80/20 970 790 70/30 880 710

The presence of zeolite thins the bath, hence the possibility of increasing the dry matter of the dispersions.

m ‘.

♦ · ««, 9 # b) Properties of coated papers

The previous layer formulas are applied to an experimental coater using the device known as a drag blade, under the following conditions: 5 · Trailer blade with reservoir. p

Blade pressure 4.2 kg / cm (

Drying temperature 75 ° C

Machine speed 40 m / min

AFNOR VII support of 70 g / m ^ 10 Deposited layer weight 11 g / m ^

The coated papers are conditioned and calendered as in Example II.

A certain number of characteristics measured on coated papers are found in Table VIII.

15 'TABLE VIII

QUANTITY ‘B R IL- SMOOTH RESIST.λ PULL-OUT A

KAOLIN / BLANCHEUR LANCE BEKK SEC IGTïmm long non ZEOLITHE AT 45 ° IN tear off - ink 3802. 100/0 82 31 1,100 91 20 90/10 82.6 27 1,190 115 90/20 83.2 25 1,270 150 70/30 83.8 20 1,340 170

The same trends are observed as in Example 2. The whiteness increases with the zeolite content, the gloss decreases, the smoothness, that is to say the surface condition, improves and the resistance to lifting increases.

110.

The zeolite therefore proves to be particularly suitable for obtaining layers of high whiteness, of moderate or matt gloss after calendering, nevertheless having a remarkable surface condition, while minimizing the rate of adhesive to be used which makes its use particularly interesting. ^ EXAMPLE 4

The comparison is made in a diaper formula containing casein as a natural binder. This is a layer formula for offset or letterpress printing.

Layer bath formula • Pigment (English kaolin and zeolite: 100 parts dry of example 1) - Dispersant: Na hexametaphosphate: 0.25 part, dry 15 Na polyacrylate t 0.2 part dry - Casein * t 6 parts in dry - Styrene butadiene latex s 10 parts in dry - Calcium stearate S 1 · part in dry - Antimoùsse. * 0.5 part as is 20 - Dry matter t 40%

The casein is dissolved using sodium hydroxide and ammonia. As in Example 3, 10, 20 and 30 parts of. .kaolin have been replaced by the zeolite defined in Example 1.

The baths are laid down using an experimental machine. 25 mental, on an AFNOR VII support of 70 g / m 2, by means of the so-called air knife method. Given the low viscosity of these baths (80 cps with the BROOKFIELD viscometer) the influence of the zeolite is of little importance at this low level of viscosity. The other properties of coated papers develop in substantially the same way, as a function of the zeolite content, as in Examples 2 and 3. Thus, a difference in whiteness of 1.7 points is noted between the all kaolin bath and the 30 parts of zeolite (83.2 against 85). The resistance to dry stripping is / Ψ 11 Λ Tl T f Λ1Λ T ** Λ 4 · · ΐ w · ·% v \ 4 · ^ J. “Λ Ο Ο —v y -” * * ·· * TAT — V ^ “a M 4 · m -¾ Λ IT ΪΊ

Claims (3)

11 1. Process for the repair of coating compositions for materials based on cellulosic fibers with a dry matter content of equal to or greater than 40, characterized in that an aqueous dispersion of a zeolite of general formula Na 2 is used , A1203> 2 = i02, x H20 in which x can vary from 1 to 8 * more particularly -from 4 to 5, having a particle distribution of less than 5 · μ, 10 with a dispersant. · * · 2. Process as rsiendiqué under 1. in which the zeolite.represent ju ^ u'à 100% of the totality of the pigments. and · 3. The dispersions tilles that defined sojus 1; "'