JPH06123098A - Production of cast coated paper - Google Patents

Abstract

PURPOSE:To obtain continuously and in high speed a highly lustered cast coated paper of high sizability, high in paper strength, with few surface defects such as pits, without causing the step of coater operation due to staining of cast drum surface. CONSTITUTION:This cast coated paper can be obtained by using a base paper whose surface pH is 5-8 and >=1.6X10<-3> (sec.m<4>/g<2>) in the value derived from dividing the Steckigt sizing degree by the square of the oven dry meter basis weight and also using, as the adhesive for the primer layer, an adhesive containing an acrylic emulsion >=70wt.% in gel content and/or a latex of the same gel content.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a cast coated paper by using a base paper which is made in a neutral region by using a sizing agent for neutral papermaking. More specifically, the present invention, when producing a cast coated paper having high size, strong paper strength and few surface defects such as pits, stop operation for removing paper scraps and stains on the surface of the cast drum. The present invention relates to a method for producing cast coated paper that enables stable continuous production without performing the above.

[0002]

2. Description of the Related Art As a method for producing cast coated paper, there are a direct method (wet casting method), a solidification method (gelling casting method), a rewetting method (rewet casting method) and the like.

The direct method is a method in which an aqueous coating solution containing a pigment and an adhesive is applied to a base paper, and then the coated surface is brought into close contact with a high-temperature mirror-finished drum surface (hereinafter referred to as a cast drum) in a wet state and dried. The coagulation method is a method in which a coagulant is added to an aqueous coating liquid and coated on the base paper, and then the coating surface is brought into close contact with the cast drum in a wet state and dried, or after coating the base paper with the aqueous coating liquid. This is a method in which a coagulant is applied and the coated surface is brought into close contact with the cast drum in a wet state and dried. The rewetting method is a method in which an aqueous coating solution is applied to a base paper, dried once, and then re-wet to bring the re-wetting surface into close contact with a cast drum to dry.

Therefore, while high gloss art paper is imparted with smoothness and glossiness by supercalendering in a dry state, cast coated paper is wet in a coated surface, that is, coated by any method. Since the layer is smoothed in a highly plastic state, a coated surface having high smoothness and higher gloss can be obtained.

In these cast coated papers, unlike general coated papers in which the coating composition is dried immediately after being coated on the base paper, the cast coated paper is wet by the heating drum until it is dried. Because tension is applied for a long time in the state,
Paper breakage is likely to occur, and for this reason, the base paper for cast coating is required to have strong paper strength, particularly wet paper strength.

Further, since cast coating paper has a large coating amount and a slow coating speed as compared with general coated paper in order to perform a cast finish, it is dried after the coating composition is coated. Since it takes a long time to get there, water in the coating composition easily penetrates into the base paper for cast coating, which is also a cause of paper breakage. For this reason, there is a demand for a high-size cast coating base paper with little water penetration.

[0007] In the conventional base paper for cast coating, an acidic paper is used in which a rosin-based sizing agent, which is a generally known acidic sizing agent for papermaking, and a sulfuric acid band are added as a fixing agent, and papermaking is performed under acidic conditions. There is.

However, it is necessary to add a large amount of a sizing agent and a sulfuric acid band in order to obtain the required high-size base paper for cast coating by the acid papermaking method, but if too much is added, the paper strength will be significantly reduced. There is a drawback that Therefore, although this decrease is usually compensated by the addition of a paper strength enhancer, it is possible to obtain a base paper for cast coating with a high level of size and strong paper strength as required today by the acid papermaking method.
It is already at the limit, and it is extremely expensive.

On the other hand, in cast coating, it is necessary to release the coated surface from the cast drum surface without resistance after the coated surface containing a large amount of water is brought into close contact with the cast drum surface and dried. This is an important requirement for obtaining a coated surface that does not have any defects.

It has been customary to provide an undercoat layer between the base paper and the cast coating layer in order to obtain a cast coating surface having uniform and high gloss without coating defects such as pinholes. ing. However, increasing the coating speed to increase the production amount increases the peeling resistance of the cast coating surface from the cast drum, so sometimes fine coating pieces are picked up on the drum surface, causing defects called pits, This led to lowering the product value by lowering the glossiness of the cast coated surface.

This phenomenon is considered as follows. In the drying after the cast coating, the cast coating layer provided on the undercoat layer is pressed against the cast drum while containing a large amount of water, but at this time, a large amount of water in the cast coating layer is cast. Moving in the opposite direction of the drum, from the primer layer to the base paper layer.

At this time, if a high-sized base paper is used, it becomes difficult for the water to pass through the base paper layer, so that a large amount of water easily accumulates in the intermediate undercoat layer, and the cast coated paper is dried, Due to the pulling force in the Z (vertical) direction of the paper surface that occurs when the cast coating film is peeled from the cast drum, the weak part of the coating film, that is, between the undercoat layer and the base paper layer, between the undercoat layer itself and the undercoat layer and the cast coating layer Fine coating film pieces are easily separated from the gap.

In order to prevent such a phenomenon, in order to improve the releasability of the cast coating surface from the cast drum, a mold releasing agent is usually applied to the surface of the cast drum before the start of the operation. The fine coating film pieces picked up gradually accumulated on the cast drum, and finally the operation had to be stopped and the surface of the cast drum had to be wiped again, which was an obstacle to stable and continuous operation.

The technique for producing the above-mentioned base paper for cast coating of high size has already been disclosed in Japanese Patent Application Laid-Open No. 1-280094, but this alone cannot eliminate the pits, and particularly high-speed coating is attempted. In that case, it was not possible to operate for a long time while maintaining good cast surface quality.

Japanese Unexamined Patent Publication No. 62-162097 discloses an example in which a latex having a gel content of 5 to 60% is contained in an undercoat layer of coated paper for rotary offset printing. The gel content in the undercoat layer of coated paper for offset printing
Although an example using a latex of 15 to 70% is disclosed, all of them have the drawback that the adhesive strength is insufficient for use in the undercoat layer of cast coating.

In order to enable high-speed production of cast coated paper, Japanese Patent Application Laid-Open No. 1-223172 discloses a technique for specifying the gel content of the latex and acrylic emulsion contained in the cast coating layer to 50% or more. However, the knowledge of the base paper and the undercoat layer is unknown because it is not mentioned at all.

Japanese Examined Patent Publication (Kokoku) No. 3-45157 discloses that a cast coated paper can be manufactured very efficiently by using a latex having a gel content of 45 to 65% of a specific composition as an adhesive for the undercoat layer. However, no specific reference is made to the base paper used.

Japanese Patent Publication No. 4-9240 discloses a gel content of 70.
Although an example of a coating composition using at least 10% latex is disclosed, the relationship between the base paper and the undercoat layer is not described at all.

[0019]

Since the size and speed of the coating machine have been increased in response to the increasing demand and productivity of cast coated paper, the quality of the base paper for cast coating has been improved. Are required to have higher size and stronger paper quality than the conventional ones.

On the other hand, recently, in addition to printing paper, the use of cast coated paper has expanded into new markets such as packaging and paper bags.
Further, there is a demand for cast coated paper having a stronger wet paper strength and higher size.

In addition, aging and discoloration of paper, which are disadvantages of acidic papermaking, have been pointed out as important problems, and conversion to neutral papermaking is becoming more and more necessary. However, it is not enough to improve only the quality of the base paper in this way, and unless the phenomenon that a fine coating film is picked up on the drum surface is also reduced, stable continuous operability and high speed of cast coating can be achieved. There is a problem of not being connected to.

Therefore, the object of the present invention is to solve the above-mentioned drawbacks of the prior art, to have a strong wet paper strength so that the paper does not break during coating, and there is no pickup of the coating film onto the drum surface during cast coating. It is an object of the present invention to provide a method for producing cast-coated paper which enables continuous coating while maintaining good cast surface quality and enables high-speed coating.

[0023]

Means for Solving the Problems The present inventors have made diligent studies in order to solve the above-mentioned problems in view of the present situation, and as a result, alkyl ketene dimer-based and alkenyl succinic anhydride-based papers were used in comparison with conventional acidic papermaking. By adding a high-performance sizing agent for neutral papermaking such as cationized starch to the pulp and making paper in the neutral range, a base paper suitable for cast coated paper can be obtained, and in addition to this , Stabilizing and speeding up the cast coating operation by optimizing the gel content of the acrylic emulsion and / or latex as an adhesive contained in the undercoat layer provided between the base paper and the cast coating layer The present invention has been completed and the present invention has been completed.

That is, the present invention provides a cast coated paper in which an undercoat coating layer containing a pigment and an adhesive as a main component is provided on at least one side of a base paper, and a cast coating layer is provided on the undercoat coating layer. In the method, the paper pH as J.TAPPI paper pulp test method No. 6-75 (coating method) as the base paper is in the range of 5 to 8 and the Steckigt sizing degree of the paper according to JIS P 8122 The value divided by the square of 1.6 × 10 ^-3 (sec
m ⁴ / g ²⁾ it is one which uses the above base paper, further the undercoat layer of the adhesive as a gel content of at least 70% acrylic emulsion and / or adhesive containing a gel content of 70% or more latex Is used to produce a cast-coated paper.

The present invention is characterized in that a neutral paper is used, whereas the base paper for cast coated paper is conventionally acidic paper. More specifically, the paper pH is J.TAPPI Paper Pulp Test Method No. According to the method specified in .6-75, CR (cresol red), BT, which is an indicator solution for measuring pH on paper, is used.
B. (Bromthymol blue), BCP (Bromcresol purple), BCG (Bromcresol green) to TBPB (Tetrabromophenol blue)
After being thinly applied to the paper and becoming semi-dry, the hue is compared with the pH standard color change table, and the paper in the range of 5 to 8 is used as the cast coated base paper.

In order to make the base paper for cast coating with neutrality, the pH of the stock is maintained near neutrality by using an alkaline chemical such as heavy calcium carbonate, light calcium carbonate, sodium hydroxide, etc. A paper may be prepared after adding a neutral sizing agent such as an alkyl ketene dimer sizing agent or an alkenyl succinic anhydride sizing agent and a cationized starch for fixing the sizing agent to the stock. Also, depending on the application
Even when the base paper is a multi-layer paper, each layer may be made in the same manner.

When the paper surface pH of the base paper is measured, the measured value differs depending on the measuring method. When the paper surface pH indicator solution according to the present invention is used, the pH of the paper stock adjusted for papermaking is 6-9. The pH of the surface of the paper which is neutral and papermaking is 5-8.

The sizing degree of the cast coating base paper produced by the above method is preferably higher in view of controlling the operability in the cast coating machine and the quality of the cast coated paper.
It is necessary to manage the sizing degree of the base paper so that it satisfies 1.

[0029]

[Formula 1] S / W ² ≥ 1.6 × 10 ^-3 (sec ・ m ⁴ / g ² )

Here, S is the Steckigt sizing degree (sec) of the base paper for cast coating, measured according to JIS P 8122, and is the average value of the measured values of the Steckigt sizing degree on the front and back surfaces of the base paper. is there. W is the absolute dry basis weight (g / m ² ) of the base paper of cast coated paper, and is measured according to JIS P8124.
After cutting it to the specified size, place it in a constant temperature dryer at 105 ° C,
The value that reached the constant weight was taken as the measured value.

If the Steckigt sizing degree of the base paper of the cast coated paper is low and the formula 1 is not satisfied, the water content in the cast coating composition permeates the base paper excessively and a paper breakage problem occurs during coating. In addition, the cast coated paper lacks sizing property, and therefore, customers will complain that they tend to tear under wet conditions.

In order to secure the sizing degree of the base paper, the effect of the present invention can also be obtained by applying a sizing agent for external addition with a size press and using the sizing agent for internal addition together with the sizing agent for internal addition. Is one way.

Next, an acrylic emulsion and / or a latex is used as the adhesive in the undercoating layer containing the pigment and the adhesive of the present invention as the main components, and the molecular weight and the degree of crosslinking of the polymer of the acrylic emulsion and the latex are used. And the percentage by weight of benzene insoluble matter in the dry film related to polarity (this value is called gel content) is 70%
The above content enables stable continuous production of cast coated paper.

In the present invention, the reason why the gel contents of both the acrylic emulsion and the latex are limited to 70% or more is that if the gel contents of both of them are less than 70%, fine coating film pieces may be generated during cast coating. It becomes easier to be picked up and gradually accumulates on the cast drum, and as a result the quality of the cast surface gradually deteriorates, and it is necessary to stop coating and wipe the cast drum again.

In the present invention, the gel content of each of the acrylic emulsion and the latex is 70% or more, and the upper limit thereof is 98%. If the gel content of the acrylic emulsion is less than 70%, the water resistance of the undercoat layer is poor, and if the gel content of the latex is less than 70%, the adhesive strength is poor, which is not suitable. On the other hand, if the gel content exceeds 98%, it may take time to manufacture the gel and it may not be easily available.

The gel content in the present invention means that a sample obtained by accurately weighing 0.3 g of a film obtained by drying an acrylic emulsion or latex at room temperature is used as a sample.
After immersing in 0 ml of benzene for 20 hours, the benzene-insoluble matter was measured, and it is shown in% by weight based on the original sample.

In the present invention, the adhesive for the undercoat layer contains an acrylic emulsion and a latex each alone or as a mixture of both, and 0.5 to 15 parts by weight of the acrylic emulsion per 100 parts by weight of the pigment, respectively. , Preferably 3 to 10 parts by weight, and latex is 0.5.
-20 parts by weight, preferably 5-15 parts by weight.

In the present invention, latex is a general term for rubber emulsions, and from this meaning, the components contained in the latex are essentially composed of diene monomers such as butadiene, isoprene and 2-chlorobutadiene. Emulsion is a general term for polymer emulsions that do not contain these diene-based monomers and that contain monomers as described below as a main component.

Aromatic alkenyl such as styrene, α-methylstyrene, chlorostyrene and dimethylstyrene is used as a copolymerizable monomer component other than the diene monomer in the latex and as a main monomer component in the acrylic emulsion. Compound and methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate,
Glycidyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycidyl methacrylate, acrylamide, N-methylol acrylamide, N-methoxymethyl acrylamide, methacryl Amide, N-methylol methacrylamide, N-methoxymethyl methacrylamide, acrylic acid, methacrylic acid, crotonic acid, fumaric acid alkyl ester, itaconic acid alkyl ester,
A mono-olefin unsaturated compound such as acrylonitrile, methacrylonitrile and vinyl acetate is used as a monomer, and these monomer components may be used in combination of two or more kinds.

The gel content of the latex can be adjusted by using mercaptans such as alkyl mercaptans and tertiary mercaptans and chain transfer agents such as carbon tetrachloride and higher alcohols. It is effective to use not only one of these but also two or more of them in combination, and the amount of these used is usually 5.0% by weight or less based on the total monomers.

The gel content of the acrylic emulsion is as follows: a monomer having a carboxyl group, a monomer having a hydroxyl group,
Monomer having a methylol group, a method of adjusting by intramolecular or intermolecular crosslinking reaction using a monomer having a glycidyl group, etc. as a sub-monomer component, and a monomer having a divinyl group as a sub-monomer There is a method of adjusting by using as a component. Either method is effective, and both methods can be used in combination.

In the above, the monomer having a carboxyl group is acrylic acid, methacrylic acid, itaconic acid, maleic acid, aconitic acid, citraconic acid and the like, and the monomer having a hydroxyl group is (meth) acrylic acid. Hydroxyethyl, hydroxypropyl (meth) acrylate and the like, the monomer having a methylol group is methylol (meth) acrylamide, methoxylmethyl (meth) acrylamide and the like, and the monomer having a glycidyl group is (meth ) Glycidyl acrylate and the like, it is preferable to use two or more kinds of these functional group-containing monomers in combination,
The amount of the monomer having a functional group based on all the monomers is usually
It is 1.0 to 10% by weight.

The divinyl group-containing monomer includes allyl (meth) acrylate, ethylene di (meth) acrylate, phenylenediacrylonitrile, divinylbenzene and the like. These may be used alone or in combination of two or more.

The above-mentioned monomer having a functional group and monomer having a divinyl group are examples, and similarly, a monomer having a reactive functional group and a monomer having a polymerizable vinyl group. If so, it can be used for the present invention.

In the preparation of the adhesive for the undercoat layer of the present invention, the above-mentioned main component monomer and the chain transfer agent or monomer which is a gel content adjusting agent are used, and a usual initiator is used as a polymerization initiation catalyst. For example, water-soluble peroxides such as potassium persulfate, sodium persulfate and ammonium persulfate, or a combination thereof with a water-soluble reducing agent such as sodium bisulfite, sodium sulfite and sodium thiosulfate can be used.

The polymerization of the monomers is usually carried out at a temperature of 50 to 100.
C., and the pressure is 0 to 10 kg / cm ^{2 in} gauge pressure. The addition of all the monomers used can be carried out by batch addition, divided addition or continuous addition. In order to stabilize the particles during polymerization, for example, an emulsifier such as sodium alkylbenzenesulfonate, sodium alkylsulfate, sodium alkylalcohol sulfate, or a protective colloid agent such as hydroxyethyl cellulose, carboxymethyl cellulose, or polyvinyl alcohol can be added. .

Examples of pigments used in the undercoating coating solution of the present invention include kaolin, clay, calcium carbonate, titanium oxide, aluminum hydroxide, zinc oxide, barium sulfate, calcium sulfate, talc, silica, plastic pigment, and satin. White and the like can be mentioned, and it is appropriately selected and selected from these.

In addition to the above acrylic emulsion and latex, casein, soybean protein, yeast protein, starch, oxidized starch and esterified starch, etherified starch, cationized starch, enzyme as an adhesive for the undercoat layer of the present invention. Examples include modified starches such as modified starches, natural adhesives such as cellulose derivatives and olefin-maleic anhydride resins, synthetic adhesives such as polyvinyl alcohol, etc., and one or more kinds of them are appropriately selected from these. .

The amount of the adhesive used in the undercoat layer is 8 to 30% by weight, preferably 10 to 20% by weight, based on the pigment used. If the amount of the adhesive used is less than 8% by weight, the strength of the coated surface will be weak, and if it exceeds 30% by weight, the cost will be high, which is not suitable for the present invention.

In the preparation of the coating liquid for the undercoat layer, various aids such as waterproofing agents, dispersants, flow modifiers, defoaming agents, coloring agents, and the like, which are added to ordinary coating liquids for coated paper, are used. The agent is appropriately selected and used as necessary to obtain desired properties.

The solid content concentration of this coating solution is generally 45 to 75.
Although it is adjusted to about wt%, considering the drying load in the dryer and the workability affected by the viscosity of the coating liquid,
It is preferably applied at a solid content of the coating solution in the range of 55 to 70% by weight. The aqueous coating solution prepared in this way is applied to one side or both sides of the above-mentioned high-sized neutral base paper.
To 30 g / m ^2, and preferably 5 to 20 g / m ² coating.

The basis weight of the base paper used in the present invention is 50 to 400 g / m 2.
^{The number is 2,} which may be single-layer papermaking or multi-layer papermaking. In other words, what is used in the form of a leaf such as a catalog or pamphlet
80 to 150 g / m ^2, also for box making, postcard, those used for card is preferably 200 to 300 g / m ² about basis weight of the base paper.

In the present invention, the undercoat coating and the drying system are not particularly limited, and a blade coater, an air knife coater, a bar coater, a roll coater, a chanplex coater, and a size used in the production of general coated papers are used. After being coated in a single layer or multiple layers on one side or both sides of the paper with a press coater, a gravure coater, etc., it is dried to a paper moisture content of 3 to 8% by weight.

The coated paper thus obtained was cast-coated as it was, or if necessary, surface-finished by using a super calender, a mat calender, etc. in an on-machine or off-machine state. Later, cast coating is applied. The undercoated paper before the cast coating is referred to as a base paper in the present invention.

In the present invention, one side may be undercoated, and then cast coated, and the other side may be uncoated and remain as the base paper surface. Both sides may be undercoated and only one side is cast coated. Alternatively, an undercoat layer and a cast layer may be provided on both sides, and either one may be used. Further, in the present invention, the cast coating itself is not particularly limited, and a conventional direct method, coagulation method, rewetting method or the like is appropriately selected and used.

[0056]

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples. The parts and% shown in Examples and Comparative Examples all represent absolute dry weight parts and absolute dry weight%. In addition, all coating amounts are shown in absolute dry weight.

Example 1 Bleached kraft pulp of softwood (NBKP) and bleached kraft pulp of hardwood (LBKP) were separately beaten to a freeness of 480 ml CSF, and NBKP: LBKP was mixed at a ratio of 15:85, and this pulp slurry was mixed. Sequentially, alkyl ketene dimer sizing agent (Kao, Cyrene) 0.20% per absolutely dry pulp, cationized starch (Oji National, Kate F) were pre-gelatinized, and 1.
2% concentration) was added to 0.60%, and a cationized polyacrylamide retention aid (made by Allied Colors, Percoll) was added to 0.02%, and the pH was adjusted to 8.8 using sodium hydroxide solution. Basis weight 105 g / m using a Fourdrinier paper machine
² of the base paper and papermaking, oxidized starch was adjusted to a concentration of 4% in the size press (Oji Cornstarch Co., Ltd., Ace A) was applied,
It was dried so that the water content was 4% to obtain a cast coated base paper.

Next, 120 parts of deionized water, 0.1 part of sodium dodecylbenzene sulfonate, 0.8 part of ammonium persulfate, 0.5 part of divinylbenzene and 40 parts of butyl acrylate as a monomer composition were placed in a nitrogen-replaced three-neck glass reactor.
Part, styrene 40 parts, acrylonitrile 17 parts, and methacrylic acid 3 parts, a total of 100 parts was charged and polymerization was carried out at 70 ° C. After 8 hours from the start of the polymerization, the polymerization rate exceeded 97%, so the reaction was stopped and after cooling. The pH was adjusted to 7 with an aqueous ammonia solution to obtain an acrylic emulsion (A1) having a gel content of 75%.

Separately, 120 parts of deionized water and sodium dodecylbenzene sulfonate were placed in an autoclave which was replaced with nitrogen.
0.2 part, potassium persulfate 0.8 part, tertiary reed decyl mercaptan (hereinafter referred to as TDM) 0.6 part, butadiene 40 parts as monomer composition, styrene 45 parts, ethyl methacrylate 8 parts and acrylic acid 2 parts as functional group monomer,
A total of 100 parts of 2 parts of acrylamide and 3 parts of hydroxyethyl methacrylate was charged and polymerization was carried out at 70 ° C. The polymerization rate exceeded 98% in 15 hours after the initiation of the polymerization, so the reaction was stopped,
After cooling, adjust the pH to 7 with sodium hydroxide and gel content
75% latex (B1) was obtained.

An aqueous coating solution having the composition shown below was applied to both sides of the base paper at 8 g / m ^{2 on} each side with a blade coater to apply an undercoat layer on both sides, followed by supercalendering at a nip pressure of 200 kg / cm to prepare a base. Paper was manufactured.

Composition of aqueous coating solution for undercoating Kaolin (manufactured by US EMC, UW-90) 30 parts Heavy calcium carbonate (manufactured, particle size 0.5 to 3 μm) 70 parts Oxidized starch (Oji Ace A 10%) 2 Part Acrylic emulsion (A1) 5 parts Latex (B1) 9 parts

To the above composition, 0.3% of sodium polyacrylate as a dispersant per pigment, 0.5% of calcium stearate as a lubricant, and 0.2% of a fluorescent dye were sequentially added, thoroughly mixed and dispersed, and a 25% aqueous ammonia solution was used. The pH was adjusted to alkaline. The solid content concentration was 60%.

Next, in order to prepare a coating liquid for casting,
0.4% of sodium polyacrylate as a dispersant was added to the following pigment composition as a dispersant and dispersed with water by a Serie deleter to prepare a pigment slurry (S) having a solid content concentration of 55%.

Pigment composition for cast coating Kaolin (US EMC, UW-90) 65 parts Heavy calcium carbonate (self-made, particle size 0.5-4 μm) 35 parts

On the other hand, casein was dissolved by heating in ammonia water to prepare an aqueous casein solution having a solid content concentration of 15%, and a coating solution was prepared in the following mixing ratio.

Coating liquid composition for cast coating Pigment (pigment slurry (S)) 80 parts Casein (casein aqueous solution) 9 parts Styrene-butadiene latex (L-1225-09 manufactured by Asahi Kasei) 10 parts Release agent ( San Nopco, wax emulsion) 1 part

Fluorescent dye was added to the coating solution for cast coating described above.
2%, antifoaming agent 0.1% and water were added sequentially and mixed well with stirring, and then adjusted to pH 9.5 with 25% aqueous ammonia to obtain an aqueous coating solution with a solid content of 40%. It was This coating liquid was coated on one side of the base paper with a roll coater so that the dry weight was 15 g / m ^2, and the coating film was immediately wiped in a wet state. It was pressed against and dried to obtain a cast coated paper. The coating speed at this time is 40
A continuous coating of 5000 m was performed at m / min. This method is generally called "direct method".

The quality of the obtained cast paper was evaluated by the following method. 1) Cast surface glossiness Measured according to JIS P 8142 (75 degree method). The larger the value, the better the gloss.

2) Contamination of the cast drum surface Visually observing the cast drum after continuous coating of 5000 m,
It evaluated as follows. ○: Clean and can be continuously coated. Δ: Some white and light dirt is attached, but a little more continuous coating is possible. X: There is a lot of dirt, and it is necessary to stop the coater and wipe the drum surface again. In addition, ◯ to Δ and Δ to × indicate the middle of each.

3) Pit of cast coated paper The surface of the cast coated paper is magnified with a loupe and visually observed,
The presence or absence of pits (fine dents in the coating film, which lacked gloss) was evaluated as follows. ○: There is no pit. Δ: There are a few pits, but the product can be barely shipped. ×: There are many pits and there is no commercial value. In addition, ◯ to Δ and Δ to × indicate the middle of each.

Example 2 Using the same base paper and cast coating solution as in Example 1, one side of the base paper was coated with a roll coater to a dry weight of 18 g / m ^2, and a solid coating film was obtained. Preliminary drying was carried out so that the concentration was 55-60%. A coagulation liquid (0.5% calcium formate aqueous solution) was applied to the surface of the coating film, and then pressed and dried on a cast drum having a surface temperature of 110 ° C. whose surface was wiped to obtain a cast coated paper. The coating speed at this time was 60 m / min. This is a method generally called "coagulation method". The quality evaluation was performed in the same manner as in Example 1.

Example 3 Using the same base paper and cast coating solution as in Example 1, one side of the base paper was coated with an air knife coater so that the dry weight was 23 g / m ^2, and the paper moisture was 5.5. Dry to wt%. A 0.3% zinc sulfate aqueous solution was sprayed onto this cast coated surface, and immediately thereafter, the surface was wiped and pressed against a cast drum having a surface temperature of 110 ° C. and dried to obtain a cast coated paper. The coating speed at this time was 100 m / min. This is a method generally called "rewetting method". The quality evaluation of the coated paper was performed in the same manner as in Example 1.

Example 4 Alkenyl succinic anhydride (Fibran made by Oji National Co., Ltd.) as a sizing agent was emulsified in the same beating pulp slurry as in Example 1 together with twice the amount of the cationized starch, and then dried. After adding 0.15% based on the weight of pulp, then 0.30% cationized starch and 0.02% cationized polyacrylamide retention aid, the pH was adjusted to 6.7 with an aqueous sodium hydroxide solution, and Example 1 was added. The base paper was made into paper in the same manner as. Thereafter, cast coated paper was manufactured in the same manner as in Example 3 and the quality of the coated paper was evaluated.

Example 5 Using the same pulp, internal additives, and size press liquid as in Example 1, a known three-layer papermaking machine was used, in which the middle layer was 50 g / m ² and both outer layers were 80 g / m ² , respectively. 210 g / m ² base paper was made into paper. Using this base paper, a cast coated paper was manufactured in the same manner as in Example 3, and the quality of the coated paper was evaluated.

Example 6 An undercoating coating solution was prepared in the same manner as in Example 1 except that the composition of the aqueous undercoating coating solution was changed as follows, and the undercoating coating and cast coating were carried out in the same manner as in Example 3. Then, cast coated paper was manufactured and the quality of the coated paper was evaluated.

Composition of aqueous coating solution for undercoating Kaolin (manufactured by EMC of the United States, UW-90) 30 parts Heavy calcium carbonate (manufactured, particle size 0.5 to 3 μm) 70 parts Oxidized starch (Oji Ace A) 2 parts Acrylic Emulsion (A1 above) 14 parts

Example 7 An undercoating coating solution was prepared in the same manner as in Example 1 except that the composition of the aqueous undercoating coating solution was changed as follows, and the undercoating coating and cast coating were carried out in the same manner as in Example 3. Then, cast coated paper was manufactured and the quality of the coated paper was evaluated.

Composition of aqueous coating solution for undercoating Kaolin (manufactured by EMC of the United States, UW-90) 30 parts Heavy calcium carbonate (self-made, particle size 0.5 to 3 μm) 70 parts Oxidized starch (Oji Ace A) 2 parts Latex (Above B1) 14 parts

Example 8 An acrylic emulsion was prepared in the same manner as in Example 1 except that the amount of divinylbenzene was changed to 1.5 parts instead of 0.5 parts in the preparation of the acrylic emulsion (A1).
An acrylic emulsion (A2) having a gel content of 95% was obtained. An undercoated paper was produced in the same manner as in Example 1 except that (A2) was used in place of the acrylic emulsion (A1), and then a cast coated paper was produced in the same manner as in Example 3. Then, the quality of the coated paper was evaluated.

Example 9 A latex having a gel content of 95% was prepared in the same manner as in Example 1 except that the amount of TDM was 0.2 part instead of 0.6 part in the production of the latex (B1). (B2)
Got An undercoat coated paper was produced in the same manner as in Example 1 except that (B2) was used instead of the latex (B1), and then a cast coated paper was produced in the same manner as in Example 3. Then, the quality of the coated paper was evaluated.

Comparative Example 1 To the same beating pulp slurry of N: L = 15: 85 as in Example 1, was added alkenyl succinic acid saponification product (Mitsubishi Petroleum, SPS300) as a sizing agent in an amount of 1.6% per absolutely dry pulp, Next, a sulfuric acid band was added in an amount of 2.5% to produce a base paper in the same manner as in Example 1. Then, cast coated paper was manufactured in the same manner as in Example 3, and the quality of the coated paper was evaluated.

Comparative Example 2 In the production of the base paper of Example 1, 0.13% of alkyl ketene dimer sizing agent (Cyrene) was added instead of 0.2% of absolutely dry pulp, and the pH was adjusted to 6.2. A base paper was made in the same manner as in Example 1 except for the above. Thereafter, cast coated paper was manufactured in the same manner as in Example 3 and the quality of the coated paper was evaluated.

Comparative Example 3 An acrylic emulsion (A3) was prepared in the same manner as in Example 1 except that 0.3 part of divinylbenzene was added instead of 0.5 part in the preparation of the acrylic emulsion of Example 1. did. The gel content of this acrylic emulsion is 60
%Met. Example 6 The composition of the undercoating coating solution of Example 6 was changed to Example 3 using (A3) instead of acrylic emulsion (A1).
A cast coated paper was manufactured in the same manner as in 1. and the quality of the coated paper was evaluated.

Comparative Example 4 In the production of the latex of Example 1, the amount of TDM was 0.6.
A latex (B3) was produced in the same manner as in Example 1 except that 0.8 part was added instead of the part. The gel content of this latex was 60%. A cast coated paper was produced in the same manner as in Example 3, except that (B3) was used instead of the latex (B1) in the composition of the undercoating coating liquid of Example 7, and the quality of the coated paper was evaluated.

The results measured and evaluated in Examples and Comparative Examples are shown in Table 1.

[0086]

[Table 1]

As is clear from the table, according to the method of the present invention, the drum surface is not contaminated, the obtained cast coated paper has no pits, the glossiness is extremely high, and the paper breaks during coating. However, when the paper surface pH was lower than 5, the drum surface was slightly soiled and the paper was broken (Comparative Example 1). If the value of / W ² is lower than 1.6 × 10 ^-3 sec ・ m ⁴ / g ² , even if the gel content of acrylic emulsion and latex is high, paper breakage will occur during coating, stains on the drum surface and cast surface Pits were generated (see Comparative Example 2).

Furthermore, the gel content of the acrylic emulsion or latex used as the adhesive for the undercoat paint is
When it is lower than 70%, the dirt on the drum surface and the pits on the cast surface increase, the glossiness of the surface of the cast coated paper decreases, and the value of the obtained product is lost (Comparative Examples 3 and 4).
reference).

[0089]

As described in detail above, according to the present invention, the pH of the paper surface is in the range of 5 to 8, and the value obtained by dividing the Steckigt sizing degree by the square of the absolute dry meter basis weight of the paper is 1.6 × 10 ^-3. sec ・ m ⁴
Using a base paper of more than / g ² and further using an acrylic emulsion having a gel content of 70% or more as an adhesive for the undercoat layer and /
Alternatively, by using latex, cast paper with high size, strong paper strength, few surface defects such as pits, and extremely high gloss is accompanied by suspension of the coating machine due to dirt on the surface of the cast drum. It has an effect that it can be manufactured continuously without high speed.

Claims (1)

[Claims] 1. A method for producing a cast coated paper, comprising providing a base coating layer containing a pigment and an adhesive as a main component on at least one side of a base paper, and forming a cast coating layer on the base coating layer. J.TAPPI paper pulp test method No. 6-
75 (coating method) paper surface pH in the range of 5-8, and JIS
The value obtained by dividing the Steckigt sizing degree of paper according to P 8122 by the square of the absolute dry meter basis weight of the paper is 1.6 × 10 ^-3 (sec ・ m ⁴ / g ² ) or more is used as the base paper. A method for producing cast coated paper, characterized in that an adhesive containing an acrylic emulsion having a gel content of 70% or more and / or a latex having a gel content of 70% or more is used as an adhesive.