JPH08183145A - Quality improvement of coated paper - Google Patents

Abstract

PROBLEM TO BE SOLVED: To coat a cellulose sheet base with two or more coatings capable of achieving a final surface of high quality having a final coating compsn. of a high solid concn. at a relatively high web speed in a coating machine. SOLUTION: A method of more simplifying the coating a cellulose sheet material coated with at least one preparatory inorg. pigment-containing coating among final inorg. pigment-containing coatings is disclosed. The compounding of a sizing agent such as an alkyleketene dimer up to 2 wt.% to preparatory coatings or at least one of them based on the wt. of inorg. pigment is included. The compsn. used in this method is also disclosed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to improving the quality of coated cellulosic sheet materials prepared by applying two or more mineral pigment-containing coating compositions to a cellulosic sheet material base.

[0002]

2. Description of the Related Art When a high-quality printed image is formed on a cellulose sheet material such as paper or cardboard, it is usually one or more of kaolin clay, calcium carbonate, calcium sulfate, titanium dioxide, barium sulfate, satin white and the like. It is necessary to apply to the surface at least one coating composition containing the mineral pigment of Application of such a coating composition improves the smoothness, gloss, whiteness and opacity of the surface to which the printed image is applied.
Often it is necessary to apply two or more layers of pigmented coating composition to obtain the desired quality of the final coated surface.

It is usually desirable to operate a coater at the maximum practical web speed in order to maximize the return on capital invested in the paper coater. Also, because the coating composition consists of pigments, adhesives, and sometimes other solid components suspended in water, it is necessary to remove the water content of the composition by thermal evaporation in order to dry the coating. In order to minimize the consumption of energy for thermal evaporation, it is desirable to handle coating compositions with the highest solids concentration possible.

[0004]

However, when a final coating composition having a relatively high solids concentration is applied to a base sheet having a relatively high moisture absorption, the excess coating composition is removed and the coating is smoothed. This final coating tends to be spoiled by scratches and other imperfections when a doctor blade is used to remove.

The object of the present invention is to apply two or more coatings to a cellulosic sheet base and to achieve a high quality final surface with a high solids concentration of the final coating composition at a relatively high web speed in a coating machine. It is to provide a way to enable.

The use of water repellent chemical reagents in the manufacture of cellulose sheet products is known. The absorption of water into sheet products can be controlled by a process known as "sizing". Generally, there are two main types of sizing process: internal sizing and surface sizing. In internal sizing, the water repellent is mixed with the pulp of cellulosic fibers prior to sheet formation. In surface sizing, a reactant, usually starch in this case, is applied to a web of sheet material that has already been formed by passing the web through a coating trough known as a "size press". Generally, in surface sizing, both sides of the web are coated with a film of water repellent.

The most commonly used sizing agent for internal sizing is rosin, which precipitates in a suspension of cellulosic fibers upon addition of aluminum sulfate. However, this treatment results in a pH of the fiber suspension of about 4-6.
Therefore, it is not suitable for use when an alkaline filler such as calcium carbonate is added to the suspension.

Neutral or alkaline pH for sizing cellulosic sheet materials containing alkaline fillers.
Sizing agents have been developed that give water-repellent properties to cellulosic fibers by value. These sizing agents include the alkylketene dimer type described in US Pat. No. 2,627,477 and the alkenyl succinic anhydride type described in US Pat.

[0009]

SUMMARY OF THE INVENTION The present invention provides at least one
Provided is a method for making it easier to apply a final inorganic pigment-containing coating to a cellulosic sheet material coated with one preliminary inorganic pigment-containing coating, the method comprising applying to the pre-coating or to at least one pre-coating. , Up to 2% by weight, based on the weight of the inorganic pigment, of a sizing agent.

The present invention also provides a method of coating a cellulosic sheet material, which method comprises at least one preliminary inorganic pigment-containing coating and then a final (finishing) inorganic pigment-containing coating. A method of coating a cellulose sheet material, wherein the precoating or at least one precoating comprises 2% by weight based on the weight of the inorganic pigment.
There are up to sizing agents.

The present invention further provides a composition for forming a preliminary inorganic pigment-containing coating on a cellulosic sheet material, the composition comprising 2% by weight, based on the weight of the inorganic pigment and the inorganic pigment. Up to sizing agent.

The sizing agent is preferably an alkyl ketene dimer of the type used as an internal size for paper under alkaline or neutral conditions. Such alkyl ketene dimers have the general formula:

[0013]

Embedded image

However, R is an alkyl group having 8 to 20 carbon atoms.

The sizing agent can also be, for example, styrene maleic anhydride copolymer, alkenyl succinic anhydride or anionic polyurethane.

The inorganic pigments in the preliminary and final coating compositions can both be selected from the group consisting of kaolin clay, calcium carbonate, titanium dioxide, calcium sulfate, barium sulfate and satin white. In addition to the inorganic pigments, both the final and pre-coating compositions are 4-20% by weight, based on the weight of the inorganic pigments.
Also included are proteinaceous adhesives such as starch, casein, and the like, and pigmentary adhesives typically selected from the group consisting of, for example, styrene-butadiene rubber or latex of acrylic polymers. The coating composition also usually contains from 0.02 to 1% by weight, based on pigment weight, of a dispersant for inorganic pigments.

The amount of sizing agent used in the precoat composition is based on the weight of the inorganic pigment.
The range of 0.01 to 0.30% by weight is preferable.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings of FIGS.

Example 1 Three coating compositions are prepared and the first two coatings are applied to a base paper to form a double coated paper. Each composition was prepared according to the general formulation shown below.

Ingredients by Weight Calcium Carbonate Pigment 100 Adhesive 15 Calcium carbonate pigment is 60% by weight and has a spherical equivalent diameter of 2
It was a ground natural marble with a particle size distribution consisting of particles smaller than μm.

The adhesive used for each of the three compositions was: A starch 15 parts by weight B starch 12 parts by weight and latex solids 3 parts by weight C starch 10 parts by weight and latex solids 5 parts by weight.

The starch is a Celesta.
It was an oxidized corn starch available under the trade name "AMISOL 05591" by r).
The latex contains 50% by weight of styrene butadiene rubber polymer and is available from Dow Chemical Company (The D
It is available under the trade name "Dow 950" from the ow Chemical Company.
The amount of latex used in the above formulation is expressed as the weight of dry polymer solids.

Each composition was divided into two parts 1 and 2. In part 1, per 100 parts by weight of calcium carbonate pigment, Hercules Corporation (the
0.25 parts by weight, on a dry weight basis, of a weak cationic alkyl ketene dimer, available under the tradename "AQUAPEL C519" by Hercules Corporation. Part 2
No alkyl ketene dimer was added to.

Each composition was applied to an unsized, absorbent, wood-free base paper by means of a laboratory paper coating machine of the type described in British Patent No. 1032536 at 400 m. It was applied at a paper speed of mim ^-1 . In each case the coating was dried by blowing air for 2 minutes.

Each sample of paper coated with the first coating composition was then coated with a second composition having the following general formulation by means of a laboratory bench blade coating machine.

Ingredients by weight Fine calcium carbonate pigment 100 Latex adhesive 12 Carboxymethyl cellulose sodium 1 Fine calcium carbonate pigment has a particle size distribution in which 95% by weight consists of particles having a sphere-converted diameter of less than 2 μm. Met. The latex adhesive was the same as that used for the first coat, and sodium carboxymethyl cellulose was available under the trade name "FINNFIX 5" by Metsa Serla. Each sample of paper coated with each of the six different first coating compositions was divided into many parts and the blade pressure in the coating apparatus was 8-20 g. ^Varying to give a series of different weights in the m ^-2 range.

The coating device was equipped with a device for monitoring the drying rate of the second coating composition by measuring the intensity of light reflected from the surface of the coated paper. Immediately after passing under the blade, the coating wets uniformly and is therefore very light reflective. However, the appearance became dull as the coating dried. An adjustable light source and detector were mounted above the coating device to obtain incident and measurement light at an angle of 75 degrees from the paper normal. The signal from the detector was applied to the input of the personal computer via a voltage measuring connector. The computer can record up to 15,000 measurements of illumination per second, so an average of 100 measurements is calculated to provide 150 data points per second,
It became each data point.

For each sample of paper to be coated, the reflected illuminance measurements were made on dry paper for about 2 seconds. The coating equipment was then turned on and the drying curve of illumination and time was recorded by the computer. A typical drying curve was that the illuminance first dropped to near zero as the blade passed under the light source and detector, followed by a rapid increase in illuminance upon exposure of the wet coating film. The illuminance then begins to decrease as the coating dries and eventually becomes constant, making a measurement of the reflection of light from the dry coated paper. For each sample of paper, the drying rate was expressed as the drying parameter δ. The δ value displays the rate of change in illuminance over time as a curve, the maximum positive slope of the illuminance / time curve when the first wet coating is sensed, and the coating with the highest rate of change in illuminance. The time interval between the maximum negative slope of this curve when partially dry was determined exactly by δ.

For each of the six first coating compositions, the graph is a plot of the drying parameter δ vs. coat weight, the results of which are shown in FIGS. FIG. 1 shows the results of the first coating compositions A1 and A2 with and without the alkyl ketene dimer, respectively. FIG. 2 shows the results of the first coating compositions B1 and B2, FIG.
2 shows the results for coating compositions C1 and C2 of FIG.

In any case, the drying parameter δ,
Therefore, the drying time increases with the coat weight, but in each sticking system used in the first coating composition, the second coat was added when the alkyl ketene dimer was added to the first coating composition. The drying speed becomes slow.

Example 2 Weight 83 g. A batch of m ^-2 absorbent wood-free base paper was made into four different first
Was pre-coated with the coating compositions of and each of the compositions was prepared with the general formulation shown below.

Ingredients by Weight Calcium Carbonate Pigment 100 Oxidized Starch Adhesive 18 Sodium Hydroxide Up to pH 8.5 Alkylketene Dimer Water shown below Up to 62% solids Calcium carbonate pigment is the first coating composition of Example It was the same as that used for the thing.

The amount of alkyl ketene dimer in the four compositions was 0, 100 parts by weight of pigment, respectively.
0.02, 0.05 and 0.1 parts by weight of active alkyl ketene dimer. The alkyl ketene dimer was the same as that used in Example 1. When using alkyl ketene dimer, at temperatures below 40 ° C., added to the composition after the starch adhesive.

The first coating composition was applied to the base paper in each case by means of a test-scale paper coating machine equipped with a roll applicator and a doctor blade.
600 m. It was applied at a web speed of min ^-1 and a blade angle of 49 degrees. The blade pressure is 10 g. It was adjusted to give a coat weight of m ^-2 . During the second coating step, the first coating composition was also added at 8.5 g. A coat weight of m ^-2 was also applied to the opposite side of the paper web.

After applying the first coating composition to each batch of paper, a line pressure of 50 kN. m ^-1 , 60 ℃, speed 600
m. Lustered by passing through two nips of a supercalender at min ^-1 .

Each sample of paper coated with the first coating composition was then coated with a second coating composition having the general formula shown below.

Ingredients by Weight Fine Calcium Carbonate Pigment 100 Styrene Butadiene Latex 12 Sodium Carboxymethyl Cellulose 1 Optical Brightener 0.5 Fine calcium carbonate pigment, latex and sodium carboxymethyl cellulose were the same as those used in Example 1.

The second coat was applied to each batch of precoated paper by a test scale paper coater equipped with a roll applicator and a doctor blade. The blade pressure is 9 g. It was held constant at the appropriate value to give a coat weight of the second coating of m ^-2 .

The runnability of the second coat, or resistance to scratches, was examined by the following method.

First, the second coat was applied to a batch of base paper which was pre-coated with the first coating composition containing no alkylketene dimer. Second
Coating composition of 9 g. web speed 300m at the maximum solid density that allows coating of m ^-2. m
It was applied in ^-1 . The web speed was then increased until the blade was scratched. When scratches are observed, the base paper is changed to a base paper pre-coated with a first coating composition containing an alkyl ketene dimer and a second
Was applied to this paper while maintaining the second coating composition and the setting of the coater. If resistance to scratches is improved, until scratches are observed or web speed is 800
m. The web speed was increased until it reached min ^-1 .

The second coating composition is then added to
It was diluted with water to a solids content of about 1-2% by weight and applied to a base paper which was pre-coated with a first coating containing no alkyl ketene dimer. This process was then repeated until no scratches were detected while applying the second coat to the base paper that was pre-coated with the first coating that did not contain the alkylketene dimer.

The entire process was then repeated with the base paper pre-coated with the first coating composition containing different amounts of alkyl ketene dimer. The results are shown in Table 1 below.

[0043]

[Table 1]

These results show that the second coating composition has a high solids concentration (68-69% by weight) on the base paper pre-coated with the first coating composition which does not contain the alkylketene dimer. It shows that the scratches were most prominent when applied at. When the second coating composition was applied at a solids concentration of 68-69% by weight, only 0.0% was used to significantly reduce the scratches.
It was sufficient to include 2 parts by weight of the alkyl ketene dimer in the first coating composition. When the first coating containing 0.1 parts by weight of alkyl ketene dimer was applied, the scratches during the application of the second coating were completely eliminated under the same conditions.

(Example 3) 94 g. Batches of m ^-2 weight absorbent wood-free base paper were pre-coated with three different first coating compositions having the formulations shown below.

1. 100 parts by weight of calcium carbonate pigment A; 15 parts by weight of oxidized corn starch. 2. 100 parts by weight of calcium carbonate pigment B; 15 parts by weight of oxidized corn starch; 0.6 part by weight of sodium salt of styrene-maleic acid copolymer.

3. 100 parts by weight of calcium carbonate pigment A; 15 parts by weight of oxidized corn starch; 0.25 parts by weight of alkenyl succinic anhydride.

Calcium carbonate pigment A is the same as in Example 1
Was the same as that used in the coating composition.

Calcium carbonate pigment B was a natural marble that was ground to a particle size distribution similar to calcium carbonate pigment A but had a low solids concentration and was in an aqueous suspension containing no dispersant.

The oxidized corn starch was the same as that used in Example 1.

The sodium salt of styrene-maleic acid copolymer is commercially available from Atochem under the trade name "S".
MA3000 ”.

Alkenyl succinic anhydride is based on Claymore Chemical Limited.
Product name "Clay size (C
LAYSIZE) PR4 ”.

In each case, 30% by weight of oxidized cornstarch was cooked for 20 minutes at 90 ° C. before addition.
It was added to the coating composition in the form of a solution.

For compositions 1 and 3, the cooked starch solution was added to an aqueous suspension containing 78% by weight of calcium carbonate pigment A and sodium polyacrylate dispersant. For Composition 3, alkenyl succinic anhydride was mixed into the composition just prior to coating.

Composition 2 was prepared by mixing 1333 g of a block containing 75% by weight of dry calcium carbonate pigment B with 6 g of the sodium salt of a styrene maleic acid copolymer. A peptized suspension of calcium carbonate pigment having a solids concentration of 74.4% by weight was obtained.

Each of the first coating compositions,
By the laboratory paper coating machine described in Example 1,
Paper speed 400 m. It was applied to a base paper at min ^-1 and a blade angle of 35 degrees. The blade angle was adjusted to 8.0 ± 0.5, if necessary, for each first composition.
g. Adjusted to give m ^-2 . The coating was dried by infrared heating in a hot air stream for 25 seconds, followed by 25 seconds of cold air blowing on the coated surface.

Each sample of paper coated with the first coating composition was then coated with a second coating composition having the general formula:

Ingredients by Weight Fine Calcium Carbonate Pigment 100 Latex Adhesive 12 Carboxymethyl Cellulose Sodium 1 Fine calcium carbonate pigment, latex adhesive and sodium carboxymethyl cellulose were the same as those used in Example 1. Each sample of paper coated with each of the three different first coating compositions was divided into many parts and the blade pressure in the bench coating apparatus was 8-20 g per unit area of the second coating composition. ． ^Varying to give a series of different weights in the m ^-2 range. First of each
A coating composition graph of is drawn from the drying parameter δ against coat weight and the results are shown in FIG. In the control of the first coating composition 1, the drying parameters remain essentially constant with the coat weight of the second composition, whereas according to the invention in the case of the first compositions 2 and 3 In, the drying parameters increase sharply with the coat weight of the second composition, indicating that the second coat dries more slowly when the sizing agent is added to the first composition.

Example 4 Weight 83 g. A batch of m ^-2 absorbent wood-free base paper was applied to three different primary
Was pre-coated with the coating compositions of and each of the compositions was prepared with the general formulation shown below.

Ingredients by Weight Calcium Carbonate Pigment 100 Oxidized Starch Adhesive 18 Sodium Hydroxide Up to pH 8.5 Sizing Agent Water Shown Below Up to 62% Solids Calcium carbonate pigment is used in the first coating composition of Example 1. It was the same as it was.

The sizing agent is Eka Nobel (Eka
Nobel) product name "CYCLO PAL (CYCLO
PAL) A "anionic polyurethane, the amounts used in the three compositions being 0, 0.1 and 0.2 parts by weight, respectively, of active anionic polyurethane per 100 parts by weight of pigment. It was polyurethane. Anionic polyurethane was added to the composition before the starch adhesive.

The first coating composition was applied to the base paper in each case by a test scale paper coating machine equipped with a roll applicator and a doctor blade at 600 m. It was applied at a web speed of min ^-1 and a blade angle of 49 degrees. The blade pressure is 10 g. m ^-2
Was adjusted to give a coat weight of In this case, the first
Coating need not be applied to the other side of the paper web. Because the paper coated on only one side is
This is because it was found that there was sufficient resistance to rolling up after glossing.

After applying the first coating composition to each batch of paper, a line pressure of 50 kN. m ^-1 , 60 ℃, speed 600
m. Lustered by passing through two nips of a supercalender at min ^-1 .

Each sample of paper coated with the first coating composition was then coated with a second coating composition having the general formula shown below.

Ingredients by Weight Fine Calcium Carbonate Pigment 100 Styrene Butadiene Latex 12 Sodium Carboxymethyl Cellulose 1 Optical Brightener 0.5 Fine calcium carbonate pigment, latex and sodium carboxymethyl cellulose were the same as used in Example 1.

The second coat was applied to each batch of precoated paper by a test scale paper coater equipped with a roll applicator and a doctor blade. The blade pressure is 9 g. It was held constant at the appropriate value to give a coat weight of the second coating of m ^-2 .

The runnability of the second coating, or resistance to scratches, was examined by the method described in Example 2. The results are shown in Table 2 below.

[0068]

[Table 2]

These results show that by including the anionic polyurethane in the first coating composition at a level of 0.1 parts by weight per 100 parts by weight of pigment, the second coating composition is about 69% solids by weight. It shows that scratches are reduced when applied at a concentration.

[0070]

In accordance with the present invention, two or more coatings of cellulose are provided in a coating machine at relatively high web speeds that allow the achievement of a high quality final surface having a high solids final coating composition. A method of applying to a sheet base can be provided.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the coating weight of the first coating compositions A1 and A2 with and without the alkylketene dimer and the drying parameter, respectively.

FIG. 2 is a graph showing the relationship between coat weights of the first coating compositions B1 and B2 and drying parameters.

FIG. 3 is a graph showing the relationship between the coat weights of the first compositions C1 and C2 and the drying parameters.

FIG. 4 is a graph showing the relationship between the coat weight of each composition and the drying index.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ulrika Elofson Cornwall P25 25 DK, Estee. Austell, Egg Cum Broad 26 (72) Inventor John Claude Husband England Cornwall P25 25 4 H.R. Estee. Austell, Parkway 32

Claims (19)

[Claims] 1. A final inorganic pigment-containing coating, comprising:
A method for simplifying application to a cellulosic sheet material coated with at least one preliminary inorganic pigment-containing coating, the method comprising the preliminary coating or at least one of the preliminary coatings. To a sizing agent up to 2% by weight, based on the weight of the inorganic pigment. 2. A method for coating a cellulosic sheet material, the method comprising coating the cellulosic sheet material with at least one preliminary inorganic pigment-containing coating and then with a final inorganic pigment-containing coating. Included in the preliminary coating or in at least one of the preliminary coatings is up to 2% by weight of sizing agent, based on the weight of the inorganic pigment. 3. The method according to claim 1, wherein the inorganic pigment is kaolin clay, calcium carbonate, titanium dioxide, calcium sulfate, barium sulfate or satin white. 4. The method according to claim 1, wherein the sizing agent is an alkyl ketene dimer. 5. The method according to claim 1, wherein the sizing agent is present in an amount of 0.01 to 0.30% by weight, based on the weight of the inorganic pigment. 6. A method according to any of claims 1 to 5, wherein the preliminary and / or final composition further comprises an adhesive. 7. The method of claim 6, wherein the adhesive is starch, a proteinaceous adhesive or a polymer latex. 8. The adhesive according to claim 6, wherein the adhesive is present in an amount of 4 to 20% by weight, based on the inorganic pigment.
The method described in. 9. A method according to any of claims 1 to 8, wherein the preliminary and / or final composition further comprises a dispersant. 10. The method according to claim 9, wherein the dispersant is present in an amount of 0.02 to 1% by weight, based on the weight of the inorganic pigment. 11. A composition for forming a preliminary inorganic pigment-containing coating on a cellulosic sheet material, the composition comprising an inorganic pigment and up to 2% by weight, based on the weight of the inorganic pigment, of a sizing agent. Composition. 12. The composition according to claim 11, wherein the inorganic pigment is kaolin clay, calcium carbonate, titanium dioxide, calcium sulfate, barium sulfate or satin white. 13. The composition according to claim 11 or 12, wherein the sizing agent is an alkyl ketene dimer. 14. The composition according to claim 11, wherein the sizing agent is present in an amount of 0.01 to 0.30% by weight, based on the weight of the inorganic pigment. 15. The method according to claim 11, wherein the preliminary and / or final composition further comprises an adhesive.
4. The composition according to any one of 4 above. 16. The adhesive is starch, a proteinaceous adhesive or a polymer latex.
The composition according to. 17. The composition according to claim 15, wherein the adhesive is present in an amount of 4 to 20% by weight, based on the inorganic pigment. 18. The composition according to claim 11, wherein the composition further comprises a dispersant. 19. The composition of claim 18, wherein the dispersant is present in an amount of 0.02-1% by weight, based on the weight of the inorganic pigment.