JP2003113596A - Method of production for aqueous solution of hydrophillic polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of production for aqueous solution of hydrophilic polymer free from undissolved substance, imparting a recording sheet excellent in quality of a coated film, applicable to production of an ink jet recording sheet which is produced in a short time. SOLUTION: This method for production of the aqueous solution of the hydrophilic polymer applied to production of the ink jet recording sheet comprises following steps: (1) a swelling step mixing/dispersing powder of at least one kind of the hydrophilic polymers with water, agitating for 5-120 min while defoaming by a centrifugal defoaming means installed on the surface of the liquid, (2) a dissolving step dissolving the mixed liquid after swelling by directly mixing with steam or continuously heating at 100-150 deg.C with a heat exchanger in the line while feeding the mixed liquid with a liquid feeding means, and (3) a defoaming step defoaming after dissolution by float defoaming the liquid in a defoaming vessel at 90-105 deg.C.

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 an ink jet recording sheet (hereinafter also simply referred to as a recording sheet) having on a support an ink receiving layer containing at least one layer of a pigment and a hydrophilic polymer. The present invention relates to a method for producing a hydrophilic polymer aqueous solution for obtaining a recording sheet having excellent coating film quality.

[0002]

2. Description of the Related Art In recent years, ink jet recording has been rapidly improving in image quality, and is approaching photographic image quality. In order to achieve such photographic image quality by ink jet recording, improvements have also been made in the aspect of recording paper, and recording paper with a minute void layer provided on a highly smooth support has excellent ink absorbability and dryness. Being excellent, it is becoming one of the closest to photographic quality.

As a recording sheet, a large amount of ink is absorbed,
Excellent water resistance, foreign matter, cracks on the sheet
It is required that there is no failure such as.

In order to increase the ink absorption amount, it is effective to reduce the amount of the hydrophilic polymer with respect to the pigment. However, as the amount of the hydrophilic polymer decreases, failures such as cracks increase. On the other hand, various technologies have been disclosed in the past, but the fundamental solution has not been reached yet.

As a hydrophilic polymer, a hydrophilic polymer having a high degree of polymerization and high water resistance is increasingly used in order to increase the physical strength with a small amount, but the solubility is poor and a great amount of production time is required. And In addition, undissolved matter is generated, which causes cracks. Further, since it has a high viscosity, bubbles cannot be removed, which causes many problems such as an increase in manufacturing time and generation of manufacturing loss.

As a method for solving such a problem, Japanese Patent Laid-Open No. 2001-71633 and the like are disclosed. Regarding the method for dispersing / dissolving a hydrophilic polymer, particularly polyvinyl alcohol which is often used in ink jet recording sheets, JP-A-9-302023 and JP-A-5-20223 are referred to.
No. 186602, JP-A-5-239221 and the like, but it is difficult to apply them to the production of a recording sheet using a recent polyvinyl alcohol having a high polymerization degree and a high foaming property.

[0007]

The present invention relates to a method for producing an aqueous solution of a hydrophilic polymer which is applied to the production of an ink jet recording sheet having an ink receiving layer comprising at least one layer of a pigment and a hydrophilic polymer on a support. Another object of the present invention is to provide a method for producing an aqueous solution of a hydrophilic polymer, which is free of undissolved hydrophilic polymer, has excellent coating film quality when formed into a recording sheet, and can be produced in a short time.

[0008]

The above-mentioned problems have been solved by the following means.

1. In a method for producing an aqueous solution of a hydrophilic polymer applied to the production of an inkjet recording sheet having an ink receiving layer containing at least a hydrophilic polymer on a support, (1) mixing at least one hydrophilic polymer powder and water After the dispersion, a step of swelling while defoaming by a centrifugal defoaming means provided on the liquid surface while stirring for 5 to 120 minutes, (2) after swelling, the hydrophilic polymer powder and water Directly mixing with the water vapor while feeding the mixed solution of (1) with the liquid feeding means, or continuously melting at 100 ° C or higher and 150 ° C or lower in the line by a heat exchanger, (3) After melting, put in a defoaming container And a step of floating and defoaming at 90 to 105 ° C., the method for producing an aqueous hydrophilic polymer solution.

2. When the mixed solution is dissolved in the dissolving step, the melting temperature T [° C.] and the pressure P [Mp in the line]
a] satisfies the following conditions, the method for producing an aqueous hydrophilic polymer solution as described in 1 above.

100 ≦ T ≦ 150 Pt ≦ P ≦ (Pt + 0.15) Pt; Water vapor pressure [Mpa] at temperature T [° C.] 3. A hydrophilic polymer aqueous solution characterized by extracting a fixed amount of the dissolved hydrophilic polymer aqueous solution from the defoaming container, and adjusting the flow rate sent from the swelling process to the dissolving process while monitoring the liquid level of the defoaming container. Manufacturing method.

4. At least one kind of the hydrophilic polymer is polyvinyl alcohol or modified polyvinyl alcohol having a polymerization degree of 2000 to 5000 and a saponification degree of 75 to 100%, and the hydrophilic polymer aqueous solution according to any one of 1 to 3 above. Manufacturing method.

The present invention will be described in detail below. Dispersion and swelling of the hydrophilic polymer powder can be achieved by using an apparatus as shown in FIGS. In FIG. 1, hydrophilic polymer powder and pure water are directly charged into a swelling container 4 from a pure water tank 2 and a polymer powder storage container 1 (a plurality of which are shown) by using a quantitative supply means 3. This is a form in which dispersion and swelling are performed.

Pure water and hydrophilic polymer powder may be directly charged into the swelling container 4 to disperse and swell therein. However, the use of the apparatus shown in FIG. 2 allows more rapid dissolution. More preferable.

That is, in FIG. 2, the hydrophilic polymer powder and the pure water are sent to the disperser 7 from the polymer powder storage container 1 and the pure water tank 2, respectively, using the quantitative supply means 3, and here they are uniformly distributed. Disperse. Several kinds of hydrophilic polymers can be used at the same time, and the polymer powders may be mixed by the powder mixer 6 and then dispersed, or may be separately sent to the disperser.

An apparatus for continuously mixing a hydrophilic polymer powder and pure water and dissolving or kneading the mixture is known, but generally, a hydrophilic polymer having a high molecular weight or a high degree of polymerization has a high foaming property, It is preferable to use the disperser described in Japanese Patent Application No. 2001-104333.

The temperature during dispersion is preferably 40 ° C. or lower, more preferably 30 ° C. or lower, and further preferably 25 ° C. or lower.

Known stirring means can be used. However, since the solution viscosity usually increases during swelling, a stirring means corresponding to low to high viscosity is preferable.

Swelling is usually 5 to 120 minutes under stirring,
It is carried out more preferably for 5 to 60 minutes, and even more preferably for 5 to 30 minutes. If the swelling time is insufficient, higher temperature will be required in the next melting step. Further, when liquid is sent, sedimentation or the like occurs in the liquid sending line, which makes stable manufacture difficult. On the other hand, if the swelling time becomes longer, the productivity will decrease. Therefore, it is necessary to select an optimum swelling time that matches the characteristics of the hydrophilic polymer.

Conventionally, gelatin having a molecular weight of 150,000 or less and polyvinyl alcohol having a degree of polymerization of 2,000 or less could be dispersed and swelled by the above-mentioned method, but the following problems occur for a polymer having a higher molecular weight and a higher degree of polymerization. It was That is, in the method described in FIGS. 1 and 2, a large amount of bubbles are generated in the swelling container and the viscosity is high, so that the defoaming cannot be completed within the time described above.

If the rotation speeds of the stirring means 5 and the disperser 7 are lowered in order to suppress foaming, lumps due to improper mixing occur and the equipment scale for the next melting step increases.

Even in the case of continuous dissolution in the line, if the content of bubbles is high, the flow rate must be increased in order to satisfy the production rate. Therefore, when the pipe length is constant, However, there is a problem that undissolved substances are generated due to insufficient dissolution time.

Further, there is a problem that the stability of the flow rate is deteriorated in the dissolving process and the dispersion of the polymer concentration becomes large if the bubbles are present.

As a result of diligent studies, we have found that the problem can be solved by adding a liquid level installed centrifugal defoaming device to the swelling container.

The defoaming device is well known in the world, and ultrasonic methods, vacuum / vacuum defoaming, centrifugal defoaming, etc. are also known as defoaming means. However, the scale of equipment is large in all of these devices, and particularly in the depressurization method, the swelling container needs to have a capacity of several times to several tens of times until the bubbles are broken. There is also a defoaming device that removes air bubbles by a cyclone system in the line, but it was difficult to send the liquid to the defoaming device due to the settling property of the swollen gel and clogging of the swollen polymer.
We have found that the object can be achieved by using the liquid surface-mounted centrifugal defoaming device 8 shown in FIG. That is, the object can be achieved by using a defoaming device having a function of (1) sucking bubbles from the liquid surface, (2) breaking bubbles by the centrifugal force of the rotating body, and (3) returning the swelling liquid to the liquid surface again. I found it. Examples of the centrifugal defoaming device having the above function include, but are not limited to, Babshut manufactured by Nisseki Mitsubishi Corp. and the like.

By using these defoaming means, a hydrophilic polymer having a higher molecular weight and a higher degree of polymerization than hydrophilic polymers such as gelatin having a molecular weight of 150,000 or less and polyvinyl alcohol having a degree of polymerization of 2,000 or less is used. The swelling of the water-soluble polymer is usually 5 to 120 under stirring.
Minutes, more preferably 5 to 60 minutes, still more preferably 5 to 3 minutes.
It is done in a short time of 0 minutes.

Next, claims 2 and 3 of the present invention will be described. The hydrophilic polymer dispersion liquid that has undergone the swelling step is continuously mixed with steam while being continuously fed, or is continuously melted in a line by a heat exchanger at 100 ° C or higher and 150 ° C or lower, and then a defoaming container. At 90 to 105 ° C., it is floated and defoamed. Such a dissolving / defoaming method is already known, for example, JP-A-3-33130 and JP-A-5-18.
6602.

An example of the dissolving process is shown in FIG. The hydrophilic polymer dispersion liquid that has completed the swelling process is sent from the swelling container 4 by the liquid sending means 9 (a mass flowmeter 10 is provided in the line). The polymer dispersion is further heated rapidly in a vapor mixer 11 provided in the line and supplied with vapor through a vapor amount control means 12, so that the melting temperature is 100 ° C. or higher. Pressure can be applied to the heat retaining tube 14 using the pressure control valve 16. The liquid dissolved in the heat retaining tube is floated and defoamed in the defoaming container 17 at 95 to 105 ° C. for a certain period of time, and then is cooled by the liquid feeding means 20 through the flow meter 21 to a desired temperature in the cooler 22 by heat exchange or the like. It is sent and finished as a hydrophilic polymer aqueous solution (solution). The heat retaining tube is equipped with a temperature monitor 13 for monitoring the liquid temperature, and a line pressure monitor 15 for monitoring the line pressure applied to the heat retaining tube between the outlet of the heat retaining tube and the pressure adjusting valve. It is equipped.
Further, the defoaming container 17 is provided with a liquid amount monitor 18 and a steam discharge port 19 for defoaming.

The polymer swelling / dispersion liquid having a high molecular weight and a high degree of polymerization contains a large amount of bubbles in the production process unless a defoaming step is provided or an antifoaming agent is used. In the case of dissolving such a liquid, if the line pressure is too low with respect to the melting temperature, the heat retaining pipe 14 is generated due to the vapor pressure.
The temperature inside will decrease. On the other hand, if the line pressure is too high, the bubbles cannot be completely removed in the floating defoaming container,
Since the solution contains bubbles, the quality of the coating film using this deteriorates. In some cases, the liquid may flow out from the vapor outlet of the defoaming container. The cause of this is unknown at this time, but it is presumed that the defoaming load varies depending on the outflow state of the solution at the outlet of the heat insulation tube. As a result of diligent study, we further found that degassing can be completed completely in the degassing container by setting the melting temperature and the line pressure so that 100 ≦ T ≦ 150 Pt ≦ P ≦ (Pt + 0.15). It was

Where T is the temperature (° C.) immediately after the steam mixer,
Pt is the vapor pressure [Mpa] of water at the temperature (T ° C.),
P is the line pressure [Mpa] of the heat retaining tube.

The melting temperature is preferably 100 to 150 ° C.,
Furthermore, 110-130 degreeC is more preferable. The pressure is P
≦ Pt + 0.1 is preferable, and P ≦ Pt + 0.05 is more preferable. Further, the dissolution time, that is, the time from the steam mixer 11 to the outlet of the heat retaining tube 14 is preferably 10 to 60 minutes, more preferably 15 to 30 minutes.

Furthermore, since the swelling liquid (hydrophilic polymer dispersion) contains bubbles, the swelling liquid (hydrophilic polymer dispersion)
It is preferable that the flow rate is monitored by a mass flow meter. The production rate (dissolution rate) is finally the liquid feeding means 2 after the defoaming container.
However, in the present invention, the liquid amount monitor 18 that monitors the liquid level in the defoaming container 17 controls the liquid feeding means 9 in order to secure the floating time of the bubbles in the defoaming container 17. It can be dissolved without generation of undissolved substances and variation in concentration. The flow rate control method is not particularly limited, but in the ordinary feedback control, the vapor amount is generally delayed as compared with the liquid flow rate control, the control of the melting temperature is difficult, and the concentration varies. Therefore, not feedback control,
As shown in FIG. 5, in the binary value within ± 10% of the set value or the three-value control within the set value + set value ± 10%, at least the speed of change to each control value should be 10 minutes or more and 60 minutes or less. A method of gradually changing the flow rate is preferable.

The method for producing an aqueous solution of a hydrophilic polymer of the present invention can be used for producing an ink absorbing layer containing a hydrophilic polymer. In particular, recently, an ink receiving layer contains fine particles of an inorganic pigment and a hydrophilic polymer. The so-called void type inkjet recording sheet has become the mainstream in terms of the amount of ink absorbed, but the production method of the present invention is applied to the method for dissolving the hydrophilic polymer used in the production of such an inkjet recording sheet. Here, the aqueous solution refers to a solution containing water as a main component, and a small amount of other organic solvent that is brought in when a small amount of additives is added in addition to the hydrophilic polymer in order to form an inkjet recording sheet or the like. Also, a system in which a hydrophilic or hydrophobic solvent other than water is mixed, that is, a system in which these solvents other than water are mixed in an amount of 10% or less is not excluded.

The hydrophilic polymer used in the present invention is, for example, gelatin or a gelatin derivative, polyvinylpyrrolidone (average molecular weight is preferably about 200,000 or more), pullulan, polyvinyl alcohol or its derivative (average molecular weight is about 20,000 or more). Preferred), polyacrylamide, polyethylene glycol (average molecular weight 10
10,000 or more), carboxymethyl cellulose, hydroxyethyl cellulose, dextran, dextrin, polyacrylic acid and salts thereof, agar, κ-carrageenan, λ-carrageenan, ι-carrageenan, xanthene gum, locust bean gum, alginic acid, gum arabic, pullulan. JP-A-7-195826 and 7
No. 9757, a polyalkylene oxide-based copolymerizable polymer, water-soluble polyvinyl butyral, or a vinyl monomer having a carboxyl group or a sulfonic acid group described in JP-A No. 62-245260, alone or in combination with these vinyl monomers. Examples thereof include polymers such as copolymers that are repeatedly contained. These hydrophilic binders may be used alone or in combination of two or more.

Of these, the hydrophilic polymer preferably used in the present invention is polyvinyl alcohol. This polyvinyl alcohol includes, in addition to ordinary polyvinyl alcohol obtained by hydrolyzing polyvinyl acetate, modified polyvinyl alcohol such as cation-modified polyvinyl alcohol having terminals and anion-modified polyvinyl alcohol having an anionic group. .

The polyvinyl alcohol obtained by hydrolyzing vinyl acetate preferably has an average degree of polymerization of 1000 or more, more preferably 2000 to 5000. In particular, those having an average degree of polymerization of 3000 to 5000 have a great effect of the present invention. The saponification degree is preferably 70 to 100%, particularly preferably 80 to 99.5%.

As the cation-modified polyvinyl alcohol, for example, a primary to tertiary amino group or a quaternary ammonium group as described in JP-A-61-10483 can be used in the main chain or side chain of the polyvinyl alcohol. Which is obtained by saponifying a copolymer of an ethylenically unsaturated monomer having a cationic group and vinyl acetate.

Examples of the ethylenically unsaturated monomer having a cationic group include trimethyl- (2-acrylamido-2,2-dimethylethyl) ammonium chloride and trimethyl- (3-acrylamido-3,3-dimethylpropyl). Ammonium chloride, N-vinyl imidazole, N-vinyl-2-methyl imidazole, N
-(3-dimethylaminopropyl) methacrylamide,
Hydroxylethyl-trimethylammonium chloride, trimethyl- (methacrylamidopropyl) ammonium chloride, N- (1,1-dimethyl-3-dimethylaminopropyl) acrylamide and the like can be mentioned.

The ratio of the cation-modified group-containing monomer of the cation-modified polyvinyl alcohol is 0.1 to 10 mol%, preferably 0.2 to 5 mol%, based on vinyl acetate.

The anion-modified polyvinyl alcohol is, for example, polyvinyl alcohol having an anionic group as described in JP-A-1-206088, JP-A-61-2.
Copolymers of vinyl alcohol and a vinyl compound having a water-soluble group as described in JP-A-37681 and 63-307979, and modification having a water-soluble group as described in JP-A-7-285265. Examples include polyvinyl alcohol.

As the nonion-modified polyvinyl alcohol, for example, a polyvinyl alcohol derivative in which a polyalkylene oxide group is added to a part of vinyl alcohol, as described in JP-A-7-9758, is disclosed.
No. 25795, a block copolymer of a vinyl compound having a hydrophobic group and vinyl alcohol, and the like.

Also, two or more kinds of polyvinyl alcohols can be used in combination depending on the degree of polymerization and the type of modification.

Examples of the inorganic fine particles include calcium carbonate, magnesium carbonate, kaolin, clay, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc hydroxide, zinc sulfide, zinc carbonate, hydrotalcite, Examples thereof include white inorganic pigments such as aluminum silicate, silica fine particles, alumina, aluminum hydroxide, boehmite aluminum hydroxide or its hydrate, and magnesium hydroxide.

Among the above fine particles, the low refractive index (1.3 to
Inorganic fine particles having an average particle size (3 to 30 nm) of 1.8) are preferable, and examples thereof include fine particles of silica, colloidal silica, calcium silicate, calcium carbonate, boehmite aluminum hydroxide, or a hydrate thereof. Silica fine particles are preferable.

In the above, the average particle size of the inorganic fine particles is obtained by observing the particle itself or the cross-section or surface of the void layer with an electron microscope, obtaining the particle size of 100 arbitrary particles, and taking the simple average value (number average). Desired. Here, each grain size is represented by its diameter assuming a circle equal to the projected area.

Silica fine particles are roughly classified into a dry method and a wet method depending on the production method, and the dry method has the same meaning as the gas phase method.
As the vapor-phase method silica fine particles, a method by vapor-phase method hydrolysis of silicon halide at a high temperature (flame hydrolysis method) and a method in which silica sand and coke are heated and reduced by an arc in an electric furnace to be air-oxidized ( Arc method) is known. The wet process silica can be obtained by generating active silica by acid decomposition of silicate, and then appropriately polymerizing it to cause aggregation / precipitation.

In the present invention, among the silica fine powders,
In particular, anhydrous silica fine particles synthesized by a vapor phase method are preferable in that porosity and strong film strength can be obtained. When the inorganic fine particles are vapor grown silica fine particles, the average particle diameter of the primary particles is preferably 3 to 30 nm, particularly 6 to 2
0 nm is the most preferable. The vapor-phase method silica fine particles can be secondary aggregated in the coating liquid to form larger particles, but in this case, the average particle diameter of the particles before secondary aggregation is 0.03.
.About.0.2 .mu.m is preferred.

The ink jet recording sheet is prepared by dissolving the hydrophilic polymer solution prepared by the above-mentioned method of the present invention to contain a hydrophilic polymer, inorganic pigment fine particles and, if necessary, various conventionally known additives and the like. A layer coating solution is prepared, and for example, US Pat. No. 2,761,419,
It is manufactured by coating on a support using a slide bead coating method using a hopper described in the above-mentioned No. 2,761,791, an extrusion coating method, or the like.

The support used for the recording sheet is a support conventionally used for ink jet recording media,
For example, paper supports such as plain paper, art paper, coated paper and cast coated paper, plastic supports, especially paper supports with both sides coated with polyolefin, and paper supports with both sides of the base paper support laminated with polyethylene, etc. It is preferable to use the body because the recorded image is close to photographic quality and a high quality image can be obtained at low cost.

[0050]

The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

Example 1 A hydrophilic polymer was dissolved using the apparatus shown in FIGS.

(1-1) Using the apparatus shown in FIG. 2, 183.0 L of pure water at a temperature of 20 ° C. was supplied by a pump, and 2.3 kg of ossein gelatin (average molecular weight 120,000) was quantitatively supplied. Was used for 6 minutes at low speed and was continuously dispersed by being sent to a disperser (flow jet mixer 300 type (pin mixer type, manufactured by Koken Powtex Co., Ltd., hereinafter referred to as FJM)). Immediately send the dispersed liquid to the swelling container.
It swelled with stirring for 0 minutes. The concentration during swelling was 11.5%. Then, using the melting apparatus shown in FIG.
Melted at 20 ° C. The flow rate of the liquid fed to the dissolution apparatus was first set so that the dissolution time would be 10 minutes, the solubility was confirmed on the outlet side of the cooler, and the set value was gradually lowered so that undissolved matter disappeared. Set the value so that the amount of liquid in the degassing tank is constant ±
Binary control of 10% was performed, and the change time was set to 30 minutes. The line pressure at the time of dissolution was 0.2 MPa, followed by defoaming in a defoaming container and cooling to 50 ° C. in a cooler to take out the dissolved liquid. Finally, dissolution time = (steam mixer-heat retention tube outlet piping volume (L)) / (liquid flow rate when there is no undissolved material (L /
Min)) was taken as the dissolution time. During this dissolution time, about 10 points of the solution on the outlet side of the cooler when dissolved were sampled with time, and the concentration was determined by a refractometer. At the same time, the presence or absence of air bubbles in the liquid was visually confirmed.

(1-2) Except for changing the following, (1-
As in 1), ossein gelatin was dispersed / swelled / dissolved. That is, as shown in FIG. 3, a centrifugal defoaming device (Nabishi Mitsubishi Babshut Co., Ltd.) was installed so that the height of the bottom of the swelling container from the liquid surface was 10 cm.
Centrifugal degassing was performed for a minute.

(1-3) Partially saponified polyvinyl alcohol (PVA-2 manufactured by Kuraray Co., Ltd.) was filled with 185.8 L of pure water at a temperature of 20 ° C. using the apparatus shown in FIG.
35: average degree of polymerization 3500, degree of saponification 88%) 18.4
kg was sent to a disperser (TK Homogenter manufactured by Tokushu Kika Co., Ltd.) for 6 minutes to disperse. Then, the mixture was stirred for 20 minutes and swollen. The concentration during swelling was 9.2%. After that, it was melted at a melting temperature of 120 ° C. by using the melting apparatus shown in FIG. The flow rate of the solution sent to the dissolution equipment is initially 1
It was set to be 0 minutes, the solubility was confirmed on the outlet side of the cooler, and the set value was gradually lowered so that the undissolved matter disappeared. Finally, dissolution time = (steam mixer-heat retention tube outlet piping volume (L)) / (liquid flow rate when there is no undissolved material (L /
Min)) was taken as the dissolution time. About 10 points of the liquid on the outlet side of the cooler when dissolved in this dissolution time were sampled over time, and the concentration was determined by a refractometer. At the same time, the presence or absence of air bubbles in the liquid was visually confirmed.

(1-4) The same procedure as (1-3) was carried out except that the centrifugal defoaming device used in (1-2) was used. (1-1) to (1-
The results of 4) are shown in Table 1.

By the defoaming apparatus of the present invention, a hydrophilic polymer aqueous solution (dissolution) having a short dissolution time and a small concentration deviation
It was found that can be manufactured.

[0057]

[Table 1]

Example 2 The melting temperature and line pressure are shown in Table 2 as (2-1) to (2-8).
Polyvinyl alcohol (PVA manufactured by Kuraray Co., Ltd.) under the same apparatus and conditions as in (1-4) of Example 1 except that
-235) was dispersed / swelled / dissolved.

[0059]

[Table 2]

The results are shown in Table 3. According to the present invention, it has been found that an aqueous hydrophilic polymer solution having no undissolved substance and no residual bubbles can be produced.

[0061]

[Table 3]

Example 3 Polyvinyl alcohol was dissolved under the same conditions as in Example 2 (2-7) except that the flow rate at the time of dissolution was changed as follows.

(3-1) The number of rotations of the liquid feeding means 9 (Honoshin Equipment Co., Ltd. Mono pump) shown in FIG. 4 was fixed to a set value and dissolved.

The liquid feeding means 20 (Honoshin Equipment Co., Ltd., Mono pump) was controlled so that the liquid amount in the defoaming container 17 was constant at the set value.

(3-2) The mass flow meter 10 shown in FIG. 4 was monitored, and the number of rotations of the liquid feeding means 9 (Hayshin Equipment Co., Ltd., Mono pump) was controlled so as to reach a set value. The liquid feeding means 20 (Hayshin Equipment Co., Ltd. Mono pump) was controlled so that the liquid amount in the defoaming container 17 was constant at the set value.

(3-3) The number of revolutions of the liquid feeding means 9 (Hayshin Equipment Co., Ltd. MONO PUMP) is used by using two values of ± 10% of the set value so that the liquid amount in the defoaming container 17 becomes constant. Was controlled and dissolved. That is, when the liquid amount in the defoaming container 17 is higher than the set value, the set value of the liquid feeding means 9 is set to -10%, and conversely, when it is low, the set value is controlled to + 10%. The time to shift to each set value (response time) was set to 10 minutes.

(3-4) to (3-6) Dissolution was performed in the same manner as in (3-3) except that the response time of (3-3) was changed. The results are shown in Table 4.

[0068]

[Table 4]

It can be seen that the methods (3-3) to (3-5) are excellent in controlling the flow rate when the hydrophilic polymer of the present invention is dissolved, because the concentration deviation is small.

[0070]   Example 4   (4-1)   (Preparation of Inorganic Fine Particle Dispersion (S-1))   Liquid A   Water 400L   Boric acid 2.9 kg   Borax 3.2 kg   5% nitric acid 1.7L   Ethanol 8.0L   P-9 (10% solution) 220L

[0071]

[Chemical 1]

The ingredients were mixed and dissolved. 170 kg of vapor-phase process silica (A300 (hereinafter referred to as A300) manufactured by Nippon Aerosil Co., Ltd.) having an average primary particle size of about 7 nm as inorganic fine particles
Prepared.

Liquid A at a rate of 8.3 kg / min and A300 at a rate of 2.2 kg / min were produced by Koken Powtex Co., Ltd.
It was supplied to FJM. Then, using RL125V (continuous wet media type crusher, manufactured by Ashizawa, hereinafter referred to as RL), the dispersion liquid obtained from FJM was supplied to the RL at 13 kg / min using a mono pump. FJM condition is peripheral speed 30m / sec, RL condition is bead diameter 0.3mm
Zirconia, residence time 3 minutes, rotor peripheral speed 13 m / s
It went in ec. The temperature of the liquid A was 5 ° C, and the temperature of the dispersion liquid emerging from the RL was 25 ° C. Water was added to the obtained dispersion liquid to adjust the silica mass concentration to 17%, and the temperature was adjusted to 35 ° C. to obtain an inorganic fine particle dispersion (S-1).

[Preparation of Hydrophilic Polymer Solution (PVA-1)] Polyvinyl alcohol (Kuraray Industry Co., Ltd .: P
21 kg of VA235) and 280 L of pure water at 25 ° C. were mixed with a stirrer in a kettle equipped with a jacket, swollen for 30 minutes, and then the jacket temperature was adjusted to 80 ° C. to dissolve for 5 hours. Then, the stirring was stopped and the mixture was cooled to 50 ° C. Some fine suspended matter was observed. Further, it was left standing for 20 hours to float and defoam to obtain a hydrophilic polymer solution (PVA-1).

[Preparation of coating liquid and preparation of recording sheet] The inorganic fine particle dispersion (S-1) was continuously added to the static mixer at 10 L / min, and the water-soluble polymer solution (PVA-1) was added at 3 L / min to a static mixer. Supply and mix. The static mixer used 24 elements. After mixing, the mixture was supplied to a kettle and 1000 L was stored with stirring.

This coating solution was supplied at a rate of 13 L / min to a slide hopper coating machine and continuously coated on a support at a thickness of 200 μm to obtain a recording sheet. The application was successful.

A paper support having both sides coated with polyethylene (having a thickness of 220 μm and containing 13% by mass of anatase-type titanium oxide in polyethylene in the polyethylene of the ink absorption layer) was used as a support immediately after coating. After cooling for 20 seconds in a cooling zone kept at ℃, 25 ℃ wind (relative humidity 15%) for 60 seconds, 45 ℃ wind (relative humidity 25%) for 60 seconds, 50 ℃ wind (relative humidity Humidity is 25%)
Sequentially dry for 60 seconds at 20 ~ 25 ℃, relative humidity 40
The humidity was controlled for 2 minutes in an atmosphere of -60%.

(Evaluation of Recording Sheet) (Evaluation of Water Absorption) The water absorption of the ink absorbing layer was measured by the following method to evaluate the ink absorbability. First, the recording paper is cut into a size of 15 cm × 15 cm, and the mass during drying (this is referred to as (a)) is measured. Then, soak it in pure water for 30 seconds, wipe the surface water, and weigh the water (this is (b)
And)) is measured. The mass (c) of only the support having no ink absorbing layer is measured. From these, the water absorption ((b)-(a)) / ((a)-(c)) was calculated as follows, and m
Converted to mass per ² . By the way, since the support is RC paper, it is assumed that the water absorption of the support itself is zero.

(Cracks) The number of cracks per 0.3 m ^{2 of the} coated surface was visually counted. The crack score is
Usually, it is considered that there is no problem in practical use if the score is 10 or less.

(4-2) A recording sheet was produced in the same manner as in (4-1) except that the method for producing the hydrophilic polymer solution in (4-1) was changed. [Preparation of Hydrophilic Polymer Solution (PVA-2)] Using the apparatus shown in FIG. 3, 183.0 L of pure water at a temperature of 25 ° C. was fed by a pump, and polyvinyl alcohol (Kuraray Industries Co., Ltd .: PVA235) 28 Disperser (Kouken Powtex Co., Ltd.) at a constant speed for 10 minutes by a constant quantity feeder of 0.2 kg
FJM) and continuously dispersed. The dispersed liquid was immediately sent to a swelling container and swelled by stirring for 30 minutes. A centrifugal defoaming device (Bab shut manufactured by Nisseki Mitsubishi Corp.) was installed so that the height of the bottom surface from the liquid surface of the swelling container was 10 cm, and centrifugal defoaming was performed for 30 minutes from the start to the end of swelling.
The concentration during swelling was 8.05%. After that, it was melted at a melting temperature of 120 ° C. by using the melting apparatus shown in FIG. The flow rate is set so that the dissolution time is 15 minutes, and binary control of ± 10% of the set value is performed so that the liquid volume in the defoaming container is constant, and the change time is 30 minutes. Set. The line pressure at the time of dissolution was 0.2 MPa, after which defoaming was performed in a defoaming container and cooled to 50 ° C. in a cooler. After cooling, about 300 L of the liquid was primarily stocked while stirring in a container with a jacket.

Table 5 shows the water absorption and cracks of the recording sheet.
Shown in. It was confirmed by the present invention that an inkjet recording sheet with excellent coating film quality can be produced with high productivity.

[0082]

[Table 5]

[0083]

EFFECT OF THE INVENTION A method for producing an aqueous hydrophilic polymer solution, which has excellent coating film quality when used as an ink jet recording sheet and can be produced in a short time, can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a polymer powder dispersion / swelling apparatus.

FIG. 2 is a view showing another example of a polymer powder dispersing / swelling device.

FIG. 3 is a view showing an example of a swelling container using a liquid surface-mounted centrifugal defoaming device.

FIG. 4 is a diagram showing an example of a melting step.

FIG. 5 is a diagram showing an example of liquid supply flow rate control by binary control.

[Explanation of symbols]

1 Polymer powder storage container 2 Pure water tank 3 quantitative supply means 4 Swelling container 5 stirring means 6 powder mixer 7 Disperser 8 Centrifugal defoaming device (liquid level installation type) 9 Liquid transfer means 10 mass flow meter 11 Steam mixer 12 Steam amount control means 13 Temperature monitor 14 Insulation tube 15 line pressure monitor 16 Pressure regulating valve 17 Defoaming container 18 Liquid monitor 19 Steam outlet 20 Liquid transfer means 21 Flowmeter 22 Cooler

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C09D 129/04 C08L 29:04 4L055 // C08L 29:04 B41J 3/04 101Y (72) Inventor Masako Kikuchi In-house F-term (reference) 2K056 FC06 2H086 BA02 BA35 4F070 AA01 AA02 AA26 AA36 AA52 AB01 AB13 CB02 CB11 4G035 AA19 4J038 CE021 GA06 GA08 HA216 HA266 HA446 MA08 MA10 A14 A02 PB11 1111 AJ04 BE07 BE08 EA20 EA23 EA24 EA30 EA33 FA22 FA30 GA09

Claims (4)

[Claims] 1. A method for producing an aqueous solution of a hydrophilic polymer which is applied to the production of an ink jet recording sheet having an ink receiving layer containing at least a hydrophilic polymer on a support, wherein (1) at least one hydrophilic polymer powder is used. After mixing and dispersing the body and water, a step of swelling while defoaming by a centrifugal defoaming means provided on the liquid surface while stirring for 5 to 120 minutes, (2) the hydrophilic polymer after swelling A step of directly mixing with a water vapor while sending a mixed solution of powder and water with a liquid sending means, or continuously melting at 100 ° C. or more and 150 ° C. or less in a line by a heat exchanger, (3) after melting And a step of floating and defoaming at 90 to 105 ° C. in a defoaming container. 2. The melting temperature T [° C.] and the pressure P [Mpa] in the line when the mixed solution is melted in the melting step.
Satisfies the following condition, the method for producing an aqueous hydrophilic polymer solution according to claim 1. 100 ≦ T ≦ 150 Pt ≦ P ≦ (Pt + 0.15) Pt; Water vapor pressure [Mpa] at temperature T [° C.] 3. The hydrophilic polymer aqueous solution after dissolution is extracted from the defoaming container in a fixed amount, and the flow rate sent from the swelling process to the dissolving process is adjusted while monitoring the liquid level in the defoaming container. A method for producing an aqueous hydrophilic polymer solution. 4. At least one kind of hydrophilic polymer is polyvinyl alcohol or modified polyvinyl alcohol having a polymerization degree of 2000 to 5000 and a saponification degree of 75 to 100%. A method for producing the hydrophilic polymer aqueous solution described.