JP2013063378A - Preparation device and preparation method for aqueous foam liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preparation device and a preparation method for an aqueous foam liquid, for preparing the stable aqueous foam liquid wherein foam breaking or the union of bubbles does not occur with high throughput.SOLUTION: This preparation device for the aqueous foam liquid is a device (b in Figure) obtained by improving a projection-equipped double cylinder type device (a in Figure) for the preparation of the aqueous foam liquid containing a foamed coating film-forming resin, and includes: a fixed projection-equipped outer cylinder S having a cooling function; and a projection-equipped inner cylinder R rotating inside the projection-equipped outer cylinder. The ratio of the outside diameter D2b (excluding projections) of the projection-equipped rotary inner cylinder to the inside diameter D1b (excluding projections) of the projection-equipped outer cylinder is 75-95%, and the occupying volume ratio of all the projections in a volume (a volume calculated by assuming that the projections are absent) between the outer cylinder and the inner cylinder is 30-50%.

Description

  The present invention relates to a method for preparing a resin-containing aqueous foam coating solution capable of forming a resin coating containing a large amount of uniform and fine bubbles.

  In recent years, there are an increasing number of fields that utilize the specific physical characteristics, thermal characteristics, and optical characteristics of a foam coating layer containing bubbles formed by applying a foam coating solution containing fine bubbles. For example, Patent Document 1 describes a high-sensitivity heat-sensitive recording paper in which a foamed coating layer is provided between a base material and a heat-sensitive coloring layer to provide heat insulation and cushioning properties.

  In order to be a foam coating layer with excellent heat insulation and cushioning, it is necessary that the volume ratio of the foam in the foam coating layer is appropriate, and in order to obtain a foam coating layer with a smooth surface, It is preferable that the size is uniform and the bubble diameter is small. In order to form such a foam coating layer, it is necessary to prepare a foam coating solution having an appropriate volume ratio of bubbles and a small bubble diameter.

  There are a chemical method and a mechanical method for preparing a foaming liquid containing a large amount of bubbles (the volume of gas is 0.1 times or more of the liquid). The chemical foaming method is a method of preparing a foaming liquid by generating a gas in the liquid by a chemical reaction. The mechanical foaming method is a method of preparing a foaming liquid by mechanically stirring and mixing the gas and the liquid. As a method, a mechanical foaming method is preferable because a reactive chemical is not used and the foam coating layer is chemically stable and is excellent in terms of economy.

  In the case of a mechanical foaming method, a foaming liquid is produced by mechanically mixing and stirring a gas and a liquid. As a device that mechanically mixes and stirs gas and liquid, a rotor type continuous foaming machine with a pin (consisting of a pin-shaped rotor with a protrusion and a pin-shaped outer cylinder tube with a protrusion is used to rotate the rotor at a high speed in a cylinder. An apparatus that stirs and mixes a liquid that has been fed and air or the like is widely used.

The above-mentioned rotor type continuous foaming machine with a pin is often used particularly for food processing, and is used for producing whipped cream, egg white meringue, bubble-containing chocolate and the like. Examples of the rotor-type continuous foaming machine with a pin used for this purpose include Aikosha turbomix, Mondo's mondomix, and the like. In fields other than food processing, a foam coating printing apparatus combining a rotor type continuous foaming machine with a pin and a screen printing machine is commercially available from Stoke.
The agitation foaming portion (foaming treatment tank) of the above-described rotor-type continuous foaming machine with a pin has a structure as shown in FIG.

  These rotor-type continuous foaming machines with pins are foaming devices designed for food applications and Braille printing applications, and for applications that require a foaming liquid with a relatively large foam diameter of several hundred μm to several mm. Is suitable. Moreover, these apparatuses are suitable for producing a foaming liquid containing a very large amount of air with respect to the liquid (foaming ratio of 3 times or more). Here, the expansion ratio is the volume of the foaming liquid / the volume of the liquid before foaming, and can be calculated as the volume of the foaming liquid (gas + liquid) / the liquid volume. A foaming liquid having a foaming ratio of 3 times or more and a foam diameter of several hundreds μm to several mm manufactured by these apparatuses is not suitable for an undercoat layer for increasing the sensitivity of thermal recording paper. Because, usually, the thickness of the heat-sensitive undercoat layer is only about several μm to several tens of μm, and when the foam diameter is several hundred μm to several mm, the smoothness of the coating surface becomes poor, the foam collapses during drying, This is because holes are sometimes formed on the surface of the coating film, and the heat-sensitive layer coating material coated thereon is sucked into the holes and the sensitivity is lowered.

  In order to reduce the bubble diameter in the foaming liquid, it is necessary to apply a strong shearing force at the gas / liquid mixing part and to refine the bubbles by mixing and dividing actions. When the shearing force is weak, the bubble diameter does not become small or the bubble diameter does not become uniform. In the case of the rotor type continuous foaming machine with a pin used for the preparation of the foaming liquid for food and printing, it is unsuitable for giving a high shearing force because the distance between the pins is designed to be wide. In order to apply a high shearing force with these devices, the rotational speed of the rotor must be very high. However, as shown in FIG. 2, the liquid is unevenly distributed outward (outer cylinder wall side) by centrifugal force. Since the gas passes through the inner side (rotor side) without being mixed with the liquid, the desired foaming liquid cannot be obtained.

  In order to give a high shearing force, it is also possible to use a dispersion stirrer having a higher shearing force, for example, an emulsifier, instead of the pin-type rotor type rotary foaming machine. For example, an emulsion disperser manufactured by IKA (rotary blade type continuous emulsifier with slits: a cylindrical type and a slit similar to the stator on the side surface in the gap between the multiple cylindrical stators with slits on the side surface. The rotor is fitted, the rotor is rotated at a high speed, and the resin-containing liquid and air are stirred and mixed when passing through the slit, whereby the air and the like are dispersed and mixed in the resin-containing aqueous raw material liquid. . In the case of this emulsifying apparatus, the foam can be miniaturized, but in order to obtain a high shearing force, the flow path of the fluid is designed to be extremely narrow and the processing flow rate is small. Therefore, it is unsuitable as a foaming liquid continuous supply apparatus used by connecting to a high-speed coating apparatus.

JP 05-032052 A

The present invention has been made in view of the above circumstances, and is a foaming apparatus capable of highly efficiently producing a foaming liquid containing a large amount of uniform fine bubbles by mechanically mixing and stirring a gas and a liquid; It aims at providing the preparation method of the resin containing water-based foam coating liquid which uses this foaming apparatus.
In particular, the present invention is a stable aqueous foaming liquid in which an aqueous raw material liquid containing a resin for forming a coating film and a water-insoluble gas are passed through a rotor-type continuous foaming machine, and foam breakage and foam coalescence do not occur. Can be manufactured with high throughput and supplied in real time to a high-speed coating apparatus, and a rotor-type continuous foaming machine having protrusions in a special arrangement state, and a foamed resin coating film formation using the rotor-type continuous foaming machine It is an object to provide a method for preparing an aqueous foaming liquid.

  The present invention capable of solving the above problems is a rotor-type continuous foaming machine having protrusions in a special arrangement state defined below, and a water base for forming a foamed resin layer using the rotor-type continuous foaming machine. The present invention relates to a method for preparing a foaming liquid.

(1) An apparatus for preparing an aqueous foamed liquid by mechanically stirring and mixing a mixed fluid composed of an aqueous raw material liquid containing a resin for forming a foamed coating film and a water-insoluble gas, and having a cooling function. The outer cylinder with protrusions and the inner cylinder with protrusions that rotate within the outer cylinder with protrusions. The outer diameter of the rotating inner cylinder with protrusions (excluding protrusions) with respect to the inner diameter of the outer cylinder with protrusions (excluding protrusions) ) Is 75 to 95%, and the occupied volume ratio of all protrusions in the volume between the outer cylinder and the inner cylinder (the volume calculated assuming that there are no protrusions) is 30 to 50%. An apparatus for preparing an aqueous foaming liquid.

(2) The gap between the projections when the projection of the outer cylinder with projections and the projection of the inner cylinder with projections are closest to each other is 0.2 to 3.0 mm. An aqueous foaming liquid preparation apparatus.

(3) The occupied volume ratio of the protrusion in the volume between the outer cylinder and the inner cylinder (the volume calculated assuming that there is no protrusion) is gradually increased from the inlet side of the mixed fluid toward the outlet side of the aqueous foam liquid. The apparatus for preparing an aqueous foaming liquid according to (1) or (2), characterized in that it is set high.

(4) A mixed fluid comprising an aqueous raw material liquid containing a foamed coating film forming resin and a water-insoluble gas is supplied to the aqueous foaming liquid preparation apparatus according to any one of (1) to (3). The dwell time calculated by dividing the space volume between the protruding outer cylinder and the protruding inner cylinder in the apparatus by the inflow velocity of the supplied mixed fluid is set to 1.0 to 15 seconds, and the preparation apparatus A method for preparing an aqueous foaming liquid for forming a foamed resin coating film, characterized in that the foaming treatment is carried out by passing the inside.

(5) The water-based raw material liquid containing the resin for forming a foamed coating film is a resin-containing raw material liquid of a resin aqueous solution system or an aqueous resin emulsion system. Preparation method of aqueous foaming liquid.

(6) The aqueous raw material liquid containing the resin for forming a foamed coating film contains a carboxy-modified styrene / butadiene copolymer latex having a particle diameter of 150 to 250 nm (4) or (5) Preparation method of the aqueous | water-based foaming liquid for foaming resin coating film formation as described in any one of.

(7) The aqueous raw material liquid containing the foamed coating film-forming resin is an aqueous raw material liquid containing a styrene / butadiene copolymer latex and a polyoxyethylene alkyl ether surfactant. The method for preparing an aqueous foaming liquid for forming a foamed resin coating film according to any one of (4) to (6).

(8) The bubble diameter in the aqueous foaming liquid that has undergone the foaming treatment by the aqueous foaming preparation device is less than 20 μm, preferably 1 to 15 μm, and the foaming ratio is adjusted to 1.1 to 2.0. The method for preparing an aqueous foaming liquid for forming a foamed resin coating film according to any one of (4) to (7).

(9) The aqueous foaming liquid for forming the foamed resin coating film is an aqueous foaming coating liquid for forming a foamed resin coating film layer between the base material and the thermosensitive coloring layer in the thermal recording paper (4) to (8). ) For preparing a foamed resin coating film.

 (10) An aqueous foam liquid for forming a foamed resin coating film prepared by the method for preparing an aqueous foam liquid described in (4) to (9) is used as a coating liquid within 5 minutes after the preparation of the aqueous foam liquid. A method for producing a base sheet for a thermal recording material, wherein the base sheet is coated and dried to form a foamed resin layer.

ADVANTAGE OF THE INVENTION According to this invention, the apparatus and method which can prepare the resin-containing aqueous | water-based foaming liquid containing a large amount of fine bubbles with uniform foam diameter continuously and with high productivity at low cost are provided. The foamed resin coating layer formed by applying the resin-containing aqueous foamed liquid on the surface of the base sheet as a coating liquid is a foamed resin coated layer having a smooth surface state and excellent heat insulation and cushioning properties. Therefore, it can be applied to various products that are required to have a layer having excellent heat insulating properties and cushioning properties, such as an intermediate layer made of a foamed resin layer for a heat sensitive recording material.
In addition, according to the present invention, a fine resin-containing aqueous foaming liquid having a uniform foam diameter can be prepared at high speed, so that the foamed resin coating layer can be formed at high speed by directly connecting the foaming apparatus to a high-speed coating machine. It can be formed on the material surface.

It is a figure which shows the structure (structure which notched a part of outer cylinder) of the general rotor-type continuous foaming apparatus with a pin. It is a figure which shows the gas-liquid separation state produced in an apparatus when a general rotor type continuous foaming apparatus with a pin is rotated at high speed. It is a preparation process figure of the aqueous foaming liquid for foaming resin coating layer formation. FIG. 2 is a cross-sectional view of a rotor-type continuous foaming device with a pin, and shows an arrangement state of pins formed on the rotor and the stator. It is sectional drawing which cut | disconnected the rotor type continuous foaming apparatus with a pin in the longitudinal direction, and is a figure which shows the arrangement | positioning state of the pin currently formed in the rotor and the stator. It is a figure which shows the example of arrangement | positioning of the pin by the side of a rotor. It is an exploded view of a rotor type continuous foaming apparatus with a pin, and is a partially cutaway view showing an arrangement state of pins of a rotor and a stator.

  Hereinafter, with reference to the drawings, an aqueous foam preparation apparatus for forming a foamed resin coating film of the present invention and a method for preparing an aqueous foam liquid for forming a foamed resin film using the apparatus will be described.

<Foaming liquid preparation device>
The foaming liquid preparation apparatus of the present invention is basically the same as the general rotor-type continuous foaming apparatus with pins shown in FIG. 1, and includes a fixed protruding outer cylinder S (stator), It is composed of an installed rotor R with protrusions (an inner cylinder with protrusions: a rotor) that rotates. As shown in FIG. 5, for example, the protrusion of the outer cylinder S and the protrusion of the rotor R are arranged so as not to collide even when the rotor rotates. Further, as shown in FIG. 4b and FIG. 7, the space between the outer cylinder S and the rotor R is set narrower than in the case of a general rotor type continuous foaming device with a pin. The material of the outer cylinder S and the rotor R is not particularly limited, but metals such as aluminum and stainless steel are preferably used from the viewpoint of strength and thermal conductivity. The outer cylinder S main body and the protrusion may be integral or separate members. Further, the outer cylinder S may be integral or a combination of a plurality of parts. The same applies to the rotor R. The method for forming the protrusion is not particularly limited. Arbitrary methods such as integral casting, machining, welding, and screwing can be used. In particular, in recent years, it has become possible to directly create a shape designed by a three-dimensional CAD with a multi-axis machine tool (machining center), so it is relatively easy to make an outer cylinder, a rotor, and a protrusion of any shape, It is possible to create an outer cylinder and a rotor having an optimal shape suitable for the purpose of foaming.
As the shape of the protrusion, a prism, a cylinder, a cone, a pyramid, a fan, or the like is preferable. The projections of the outer cylinder S and the rotor R may be similar in shape or completely different.

<Ratio between outer cylinder inner diameter and rotor outer diameter>
In many commercially available foaming apparatuses for food, the ratio of the rotor outer diameter (not including protrusions) to the outer cylinder inner diameter (not including protrusions) is often about 40-70%. For example, in the shape as shown in FIG. 4a, the outer diameter D2 of the inner cylinder R with respect to the inner diameter D1 of the outer cylinder S is about 40-70%. This is because, when the bubble diameter may be large, it is suitable for efficiently producing a foaming liquid having a high expansion ratio. With such a device, when trying to obtain a foaming liquid with a fine bubble diameter, if the rotational speed of the device is increased, the gas G and the liquid L can be separated and flow easily by centrifugal force as shown in FIG. Is less likely to occur. In addition, the peripheral speed is different between the inside and the outside, and the shearing force is weak on the inside, so that it is difficult to obtain uniform and fine foaming. In contrast, in the present invention, the ratio of the outer diameter D2b (excluding protrusions) of the rotor R to the inner diameter D1b (excluding protrusions) of the outer cylinder S is 75 to 95% as shown in FIG.

When the ratio of the outer diameter (excluding protrusions) of the rotor R to the inner diameter (excluding protrusions) of the outer cylinder S is selected in this way, it is difficult for gas-liquid separation to occur, and the fluid receives a substantially uniform shearing force. Bubbles are uniformly refined. In addition, most of the fluid passes through the vicinity of the cooled outer cylinder, which is efficient in absorbing heat generated by friction.
If the ratio of the outer diameter of the rotor (excluding protrusions) to the inner diameter of the outer cylinder (excluding protrusions) exceeds 95%, the gap between the outer cylinder S and the rotor R becomes too narrow to obtain a sufficient processing amount. Is very inefficient because the overall diameter must be very large.

<Distance between protrusion on outer cylinder and protrusion on rotor>
In the foamed liquid preparation apparatus of the present invention, when the rotor rotates and the outer cylinder projection and the rotor projection are closest to each other, the maximum shearing force is generated on the adjacent surfaces. Therefore, the distance (clearance) between the protrusion on the outer cylinder and the protrusion on the rotor at this time is an important factor that affects the foaming state. FIG. 5 shows an example of the distance (C) between the protrusion of the outer cylinder S and the protrusion of the rotor R. Note that depending on the shape of the protrusion, the closest distance between the protrusion on the outer cylinder and the protrusion on the inner cylinder may not necessarily be the position shown in FIG.
From the viewpoint of shearing force, when the outer cylinder protrusion and the rotor protrusion are closest to each other, the closest distance between the two is better, but if it is too close, the liquid will deteriorate due to excessive shearing force. Or the volume of the liquid existing between adjacent surfaces is reduced and the processing capacity is reduced. If the distance is too close, it is difficult not only to manufacture the device in terms of mechanical processing accuracy, but also prone to problems such as protrusions coming into contact due to temperature rise or vibration during use. On the other hand, if it is too wide, the shearing force necessary for miniaturizing the bubbles cannot be obtained in a practical rotational speed region. It is desirable that the gap between the protrusions is 0.2 to 3.0 mm when the protrusions of the protrusion-provided outer cylinder and the protrusions of the protrusion-provided inner cylinder are closest to each other.

  In commercially available foaming apparatuses, the closest distance between the outer cylinder upper protrusion and the rotor upper protrusion is often constant from the fluid inlet side to the outlet side, but in the present invention it is not necessarily constant. Since the bubbles in the foaming treatment tank become finer from the inlet side toward the outlet, the protrusions of the outer cylinder protrusion and the rotor upper protrusion are also agitated and sheared so as to become stronger as the bubbles become smaller. A closest distance may be set. The closest distance between the outer cylinder upper protrusion and the rotor upper protrusion is adjusted by the shape (shape, thickness) of the protrusion and the arrangement of the protrusion.

<Occupied volume of protrusion>
In many commercially available foaming apparatuses for food, the ratio of the occupied volume of protrusions to the space between the outer cylinder and the rotor (the volume calculated as having no protrusions) is often about 20%. This is because in the case where the bubble diameter may be large, increasing the internal volume is more efficient for mixing a large amount of air into the liquid. Also, the larger the internal volume, the less the pressure loss inside, and it is suitable for processing a large amount of viscous liquid.

On the other hand, in the present invention for the purpose of preparing a foaming liquid containing fine bubbles with high productivity, the ratio of the occupied volume of the projection to the space between the outer cylinder and the rotor (the volume calculated as having no projection) 30 to 50%. The ratio of the occupied volume is adjusted by appropriately adjusting the number of protrusions, the shape of the protrusions, the distance between the protrusions, and the distance between the rotor and the outer cylinder.
If the ratio of the volume occupied by the protrusion to the space between the outer cylinder and the rotor (the volume calculated as having no protrusion) is larger than 50%, the amount of fluid in the foaming tank is reduced and the flow path is also narrowed. The amount of processing is reduced. In order to compensate for this, the apparatus itself must be enlarged, which is inefficient. On the other hand, if it is smaller than 30%, the stirring and shearing effects of the protrusions on the fluid are not sufficient, and a fine foaming liquid cannot be obtained.

<Arrangement of protrusions>
In the foaming liquid preparation apparatus of the present invention, the protrusions may be evenly installed from the fluid inlet to the outlet in the same manner as a commercially available foaming apparatus. However, it is preferable to dispose from coarse to dense from the inlet side to the outlet because it is efficient). That is, it is efficient if the ratio of the occupied volume of the protrusion to the space between the outer cylinder and the rotor (the volume calculated as having no protrusion) is increased gradually or stepwise from the fluid inlet to the outlet. . This is because the mixed state of fluid and gas is not sufficient on the inlet side, and it becomes finer as it goes to the outlet side. Therefore, the protrusions are arranged so that the stirring and shearing force are increased according to the stage of finer foam. This is because the processing capacity of the apparatus can be increased. As a method of increasing the arrangement of the protrusions from coarse to dense, it can be achieved by increasing the number of protrusions or increasing the protrusions themselves to narrow the gaps. FIG. 6 shows an example of a foamed layer rotor in which the proportion of the volume occupied by the protrusions is increased gradually or stepwise from the fluid inlet to the outlet by increasing the number of protrusions.

<Cooling>
It is desirable that the “foaming liquid preparation device” is provided with a cooling jacket or the like on the outside thereof, and a cooling medium is flowed to cool the foaming station preparation device. The cooling efficiency may be increased by cooling the cooling liquid through the protruding rotor of the foaming liquid preparation apparatus.
The cooling method of the cooler which cools a foaming liquid preparation apparatus is not specifically limited. Ordinary cooling methods such as water cooling, air cooling, and cooling with a Peltier element can be employed. The cooler may be integrated with the outer cylinder with projections of the foaming liquid preparation apparatus or may be separate. In particular, the outer cylinder of the foaming liquid preparation device has a double tube structure or a structure in which a cooling jacket is installed on the outside, so that the cooling liquid is brought into contact with the outer wall of the outer cylinder with protrusions to perform heat exchange and cool down. The method is efficient.

The preparation method of the aqueous foaming liquid for foamed resin coating film formation of this invention can be implemented according to the process of FIG.
In the process diagram of FIG. 3, reference numeral 1 denotes a “raw material solution preparation tank” for preparing an aqueous material solution containing a coating film forming resin. In the “raw material solution preparation tank 1”, an aqueous raw material solution containing a coating film forming resin is prepared. The prepared aqueous raw material liquid is sent by the “pump 2” to the “foaming liquid preparation device 3” having the “cooling jacket 4”, and supplied from the “gas storage tank 5” via the “flow rate adjusting valve 6”. Aqueous foaming liquid in which bubbles are formed is prepared by stirring and mixing with a gas such as nitrogen or air. An aqueous foaming liquid is apply | coated on a base material with the coating apparatus 8 (coating head).

There are no particular restrictions on the types of “raw material solution preparation tank 1” and “drive motor M”. The temperature of the raw material liquid prepared in the “raw material liquid preparation tank 1” is maintained at a temperature at which it can be handled in a liquid state. The prepared resin-containing aqueous raw material liquid absorbs heat generated by stirring and the temperature rises, so the raw material liquid is prepared within a range that does not cause freezing and extreme increase in viscosity that impede liquid handling. It is preferable to cool from the outside of the tank 1.
“Pump 2” that sends an aqueous raw material solution made of resin aqueous solution or resin emulsion prepared in “raw material solution preparation tank 1” to “aqueous foam preparation apparatus 3”, air, nitrogen gas, etc. from “gas storage tank 5” There is no limitation on the type of the “flow rate adjusting valve 6” sent to the “aqueous foam preparation apparatus 3”.
The gas sent from the “gas storage tank 5” by the “flow rate adjusting valve 6” is supplied to the aqueous raw material liquid supply path in FIG. 3, but the gas is different from the aqueous raw material liquid supply path. It is also possible to supply to the “aqueous foam preparation apparatus 3” from the supply route, and stir and mix together with the aqueous raw material liquid to perform foaming treatment.

  The “foaming liquid preparation device 3” performs mechanical stirring while continuously supplying gas and liquid in a closed system, and disperses the gas such as air in the resin-containing aqueous raw material liquid as fine bubbles. It is a device that can be mixed. This is a double-cylindrical type with protrusions, which consists of a rotating inner cylinder (rotor) with protrusions and a fixed outer cylinder (stator) with protrusions. And agitation and mixing between the projections on the rotor rotating at high speed and the projections of the fixed outer cylinder, and the air is dispersed and mixed in the resin-containing aqueous raw material liquid to produce a foamed liquid.

<Residence time>
In the foaming method of the present invention, the residence time of the fluid to be foamed in the foaming liquid preparation apparatus is preferably 1.0 to 15 seconds. The residence time in the foaming liquid preparation apparatus is obtained by dividing the space volume between the outer cylinder and the inner cylinder by the processing fluid inflow velocity. For example, if the total inflow of gas and liquid is 1000 mL / min and the space volume between the outer cylinder and the inner cylinder is 100 mL, it is 1/10 min, that is, 6 seconds. When the residence time in the foaming liquid preparation apparatus is shorter than 1 second, the fluid exits from the apparatus without receiving sufficient stirring and shearing action, and fine bubbles cannot be obtained. On the other hand, if it exceeds 15 seconds, it is often undesirable that the fluid is altered or overheated in the foaming apparatus. Further, in order to increase the residence time in the foaming liquid preparation device, the device is made larger with respect to the fluid flow rate. Therefore, an excessively long residence time is not desirable from the viewpoint of economy.

In the method of the present invention, the rotational speed of the rotor drive motor M of the foaming liquid preparation apparatus, the aqueous raw material liquid and air, etc., depending on the composition and properties (viscosity, surfactant addition rate, type) of the resin-containing aqueous raw material liquid The size of bubbles in the aqueous foaming liquid can be adjusted by appropriately setting the residence time (stirring time) in the apparatus. For example, when the rotation speed is constant and the ratio between the amount of raw material liquid supplied to the apparatus and the amount of air is the same, the bubble size tends to decrease as the stirring time in the apparatus increases. The expansion ratio can be adjusted by selecting the ratio of the amount of raw material liquid supplied to the apparatus and the amount of air.
The pressure loss in the foaming liquid preparation apparatus is calculated as the difference between the pre-introduction pressure measured by the “inlet side pressure gauge 7a” and the outlet side pressure value by the “outlet side pressure gauge 7b” in FIG.

<Rotation speed of drive motor M>
In the method of the present invention, the rotation speed of the stirrer drive motor M of the “foaming liquid preparation device 3”, the aqueous raw material liquid, depending on the composition and properties (viscosity, surfactant addition rate, type) of the aqueous raw material liquid containing the resin The size of the bubbles in the aqueous foaming liquid can be adjusted by appropriately setting the residence time (stirring time) in the apparatus such as air. For example, when the rotation speed is constant and the ratio between the amount of raw material liquid supplied to the apparatus and the amount of air is the same, the bubble size tends to decrease as the stirring time in the apparatus increases. The expansion ratio can be adjusted by selecting the ratio of the amount of raw material liquid supplied to the apparatus and the amount of air.

  In order to produce a foam coating liquid in which the volume ratio of bubbles is controlled, it is necessary to mechanically mix and stir the gas and liquid while continuously feeding the gas and liquid into the closed system. When the gas and liquid are mechanically mixed and stirred in an open system, it is difficult to control the volume ratio of the bubbles because air in the atmosphere may be involved during stirring. Moreover, in order to produce a foaming coating liquid having a small bubble diameter, high-speed rotation is required in order to give a strong shearing force at the gas-liquid mixing portion. In a rotating device such as a stirrer, a mechanical seal is used to mechanically seal leakage from a rotating shaft that penetrates the pressure vessel.

  The basic structure of the mechanical seal is composed of a rotating ring that can move in the axial direction by a spring or the like, and a fixed ring. The sliding surfaces perpendicular to the axes of both rings come into contact with each other and rotate relatively. Thus, it serves to minimize fluid leakage. In order to remove the frictional heat generated by this sliding, the mechanical seal requires cooling water. When the rotation speed is high, the coating material easily enters the sliding surface of the seal, and the resin dispersion is dispersed and broken (aggregated) on the sliding surface, and the coating material adheres and accumulates on the sealing surface. As a result, there is a possibility of causing a sealing failure trouble that the sealing water is mixed into the foam coating liquid. When the sealing water is mixed into the foamed coating liquid, the coating liquid is diluted, and as a result, bubble breakage, foam coalescence, etc. are likely to occur, which may be disadvantageous for miniaturization of the bubbles.

  According to the method of the present invention, the gas is mechanically mixed and stirred while continuously supplying the gas and the water-based resin aqueous solution or water-based resin emulsion-based aqueous raw material liquid into the closed system, thereby causing a sealing failure trouble. Therefore, it is possible to produce fine bubbles, and it is possible to continuously produce a heat-sensitive recording material having a foam coating layer obtained by applying and drying a foam coating solution as a heat-sensitive undercoat layer.

<Aqueous raw material liquid>
The aqueous raw material liquid is preferably a resin water-soluble or aqueous resin emulsion-based raw material liquid. Among them, it is preferable to contain a styrene / butadiene copolymer latex. Styrene / butadiene copolymer latex is relatively inexpensive and has a relatively small effect on heat-sensitive color developability, and is therefore effective as a foam coating layer resin. Moreover, since it is easy to obtain relatively fine bubbles, the film thickness of the foam coating layer can be reduced, which is advantageous in terms of cost.

  Of course, various aqueous resins can be used in combination with the styrene / butadiene copolymer-based latex as appropriate, as long as the effects of the present invention are not impaired. Examples of aqueous resins that can be used in combination include fully (partially) saponified polyvinyl alcohol, silicon-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, sodium polyacrylate, carboxymethylcellulose, polyvinylpyrrolidone, casein, and styrene- Water-soluble resin such as alkali salt of maleic acid copolymer, sodium alginate, alkali salt of acrylic acid amide / acrylic acid ester / methacrylic acid copolymer, acrylic resin latex, colloidal silica-containing acrylic resin latex, polyester polyurethane Water-dispersible resins such as latex, polyether polyurethane latex, vinyl chloride / vinyl acetate copolymer latex, ethylene / vinyl acetate copolymer latex, etc. It is. Although it does not specifically limit as content of aqueous resin, 20 mass% or more is preferable with respect to the total solid of a foam coating layer.

When a styrene / butadiene copolymer latex is used, the average particle size is preferably 150 to 250 nm. If the average particle diameter of the copolymer latex exceeds 250 nm, the fluidity of the foamed coating liquid containing the copolymer latex is lowered, and there is a possibility that the coating operation may be hindered. Further, when the average particle size of the copolymer latex is less than 150 nm, in the method of preparing the foam coating liquid at high speed rotation, dispersion failure (aggregation) of the resin dispersion occurs on the sliding surface of the seal, and the sealing surface As a result, the coating material adheres and accumulates, and as a result, there is a possibility of causing a sealing failure problem that the sealing water is mixed into the foam coating liquid.
The average particle size of the copolymer latex can be adjusted by the type and amount of emulsifier, the type and amount of polymerization initiator, the type and amount of monomer having a polar group, the monomer concentration, the polymerization temperature, etc. it can. The average particle diameter of the obtained copolymer latex can be obtained by a conventional method with a submicron analyzer (model N4) manufactured by Coulter.

It has also been found that it is preferable to contain a polyoxyethylene alkyl ether surfactant as the surfactant. Polyoxyethylene alkyl ether surfactants are particularly effective for the dispersion stability of styrene / butadiene copolymer latex. Examples of the polyoxyethylene alkyl ether surfactant include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether.
The amount of the polyoxyethylene alkyl ether surfactant used is preferably 0.3 to 20% by mass, more preferably 0.5 to 10% by mass with respect to 100% by mass of the total solid content in the resin-containing liquid. %. If the addition amount of the polyoxyethylene alkyl ether surfactant is less than 0.3% by mass, the effect is not exhibited, and even if the addition amount of the polyoxyethylene alkyl ether surfactant exceeds 20% by mass. , The effect is saturated, but rather economically disadvantageous

<Formation of foamed resin coating layer>
A foamed resin coating layer can be formed on a sheet using the aqueous foaming liquid produced by the method of the present invention as a coating liquid. As a method for forming the foamed resin coating layer on the sheet, a conventionally known method can be used. For example, extrusion molding, injection molding, coating molding, etc. can be used. In particular, a coating molding method for obtaining a foamed resin-coated sheet by coating and drying an aqueous foam coating solution on a sheet is preferable because of its high productivity.
In the case of coating molding, a foamed coating liquid is applied to a support using a coating head, and then moisture and solvent are removed by a drier to form a foamed resin coating layer on the support. At this time, the foamed resin coating layer can be peeled from the support to obtain a single foamed sheet composed of the foamed resin coating layer.

  Coating methods include bar coating, air doctor coating, blade coating, squeeze coating, air knife coating, roll coating, gravure coating, transfer coating, comma coating, smoothing coating, and microgravure. Examples include coating method, reverse roll coating method, multi-roll coating method, dip coating method, rod coating method, spray coating method, gate roll coating method, falling curtain coating method, slide coating method, fountain coating method, and slit die coating method. It is done.

  Hereinafter, although the specific preparation method of the aqueous | water-based foam coating liquid of this invention is demonstrated based on an Example, this invention is not limited by these Examples. In the examples and comparative examples, “parts” and “%” represent “parts by mass” and “mass%”.

<Example 1>
In the preparation step of the aqueous foam liquid of FIG. 3, an aqueous raw material liquid having the following composition is prepared in the aqueous raw material liquid preparation tank 1, and sent to a double-cylindrical “foamed liquid preparation apparatus 3” with a projection described later for foaming treatment. did.

[Aqueous raw material liquid]
100 parts water-dispersible polyurethane resin (trade name: Adekabon titer HUX-381, manufactured by Asahi Denka Kogyo Co., Ltd.) Foam stabilizer: higher fatty acid ammonium salt (trade name: F-1) 5 parts (Product name: AG gum, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 3 parts From the mixture of the above components uniformly mixed, 31 parts are taken, and water is added to make the total amount 100 parts. did.

[Foam preparation equipment]
Install the rotor (generator) and outer cylinder (jacket) of “Pacific Kiko Milder Emulsifier MDN304” [Horizontal (Horizontal Rotating Shaft) Rotating Three-stage Slit Blade Type Emulsifier] instead of the following rotor and outer cylinder. , “Foamed liquid preparation device 3”.
Rotor: cylinder with protrusions with an outer diameter of 175 mm (excluding protrusions), protrusion height 4.8 mm
Outer cylinder: cylinder with protrusions with an inner diameter of 185 mm (excluding protrusions), protrusion height 4.8 mm
Cylindrical part length: 100mm
Rotation speed: 2000rpm
Protrusion volume ratio: 47%
Distance between protrusion in outer cylinder and protrusion on rotor (C): 0.5 mm

Together with the aqueous raw material liquid having a flow rate of 600 ml / min, air whose flow rate was adjusted to 300 ml / min in terms of atmospheric pressure by the flow control valve 6 was sent from the gas storage tank 5 to the foaming liquid preparation device 3 and mixed and stirred to obtain a foaming treatment liquid. (Residence time: equivalent to 10 seconds).
Cooling water at 10 ° C. was allowed to flow through the cooling jacket 4 installed on the outer cylinder of the foaming liquid preparation apparatus 3 to cool the foaming liquid preparation apparatus 3. When the specific gravity of the aqueous foaming liquid sent out from the foaming liquid preparation apparatus 3 was measured and the foaming ratio was determined, the foaming ratio was 1.45. The aqueous foam was dropped on a glass plate and spread, and the bubble diameter was measured with a digital microscope.
Table 1 shows the measurement results of “foaming ratio”, “foam diameter”, and “foaming liquid temperature” in the prepared aqueous foaming liquid.

<Example 2>
In the method of Example 1, an aqueous foaming liquid was prepared in the same manner as in Example 1 except that the rotor and outer cylinder of the foaming liquid preparation apparatus 3 were changed to the following.
Rotor: cylinder with protrusions with an outer diameter of 157 mm (excluding protrusions), protrusion height of 13.0 mm
Outer cylinder: cylinder with protrusions with an inner diameter of 185 mm (excluding protrusions), protrusion height of 13.0 mm
Cylindrical part length: 100mm
Protrusion volume ratio: 40%
Rotation speed: 2000rpm
Distance between protrusion in outer cylinder and protrusion on rotor (C): 0.5 mm
Aqueous raw material flow rate: 1800 ml / min
Air flow rate: 900ml / min
Residence time: 10 seconds Table 1 shows the measurement results of “foaming ratio”, “foam diameter”, and “foaming liquid temperature” in the prepared aqueous foaming liquid.

<Example 3>
In the method of Example 1, an aqueous foaming liquid was prepared in the same manner as in Example 1 except that the foaming liquid preparation apparatus 3 was changed to the following.
Rotor: Cylinder with protrusions with outer diameter 141 mm (excluding protrusions), protrusion height 20.8 mm
Outer cylinder: cylinder with protrusions with an inner diameter of 185 mm (excluding protrusions), protrusion height of 20.8 mm
Cylindrical part length: 100mm
Protrusion volume ratio: 32%
Rotation speed: 2000rpm
Distance between protrusion in outer cylinder and protrusion on rotor (C): 0.5 mm
Aqueous raw material flow rate 4500ml / min
Air flow rate 2250ml / min
Residence time: 10 seconds Table 1 shows the measurement results of “foaming ratio”, “foam diameter”, and “foaming liquid temperature” in the prepared aqueous foaming liquid.

<Comparative Example 1>
In the method of Example 1, the following rotor-type foaming machine with food pins was used as the foaming liquid preparation device 3, and the same procedure as in Example 1 was performed except that the aqueous raw material liquid flow rate and air flow rate were changed as follows. An aqueous foaming solution was prepared.
Double cylindrical continuous foaming machine with food pin (Mondmix foaming machine manufactured by Mondmix)
Rotor: a cylinder with a pin with an outer diameter of 34 mm (excluding the pin), pin height 20 mm
Outer cylinder: A cylinder with a pin with an inner diameter of 81 mm (excluding the pin), a pin height of 20 mm
Cylindrical part length: 200mm
Pin part volume ratio: 20%
Rotation speed: 2000rpm
Distance between pin in outer cylinder and pin on rotor (C): 5mm
Aqueous raw material liquid flow rate 2715 ml / min
Air flow rate 1357ml / min
Residence time: 10 seconds Table 1 shows the measurement results of “foaming ratio”, “foam diameter”, and “foaming liquid temperature” in the prepared aqueous foaming liquid. Since the gas exited the foaming tank without being completely mixed with the liquid, the predetermined foaming ratio was not reached. Further, a foaming liquid having a large bubble diameter and fine bubbles could not be obtained.

<Comparative example 2>
In the method of Example 1, an aqueous foaming liquid was prepared in the same manner as in Example 3 except that the following rotor-type foaming machine with a pin was used as the foaming liquid preparation apparatus 3.
Foaming liquid preparation apparatus: The rotor (generator) and outer cylinder (jacket) of “Miheida emulsifier MDN304 type manufactured by Taiheiyo Kiko” were installed in place of the following rotor and outer cylinder, and used as “foaming liquid preparation apparatus 3”.
Rotor: Cylinder with protrusions with outer diameter 141 mm (excluding protrusions), protrusion height 20.8 mm
Outer cylinder: cylinder with protrusions with an inner diameter of 185 mm (excluding protrusions), protrusion height of 20.8 mm
(The outer cylinder was installed in two parts so as to sandwich the rotor.)
Cylindrical part length: 100mm
Protrusion volume ratio: 70%
Rotation speed: 2000rpm
Distance between outer cylinder protrusion and rotor protrusion (C): 0.5 mm
Aqueous raw material flow rate 1800ml / min
Air flow rate 900ml / min
Residence time: 10 seconds Table 1 shows the measurement results of “foaming ratio”, “foam diameter”, and “foaming liquid temperature” in the prepared aqueous foaming liquid.

<Comparative Example 3>
In the method of Example 1, the following rotor-type foaming machine with a pin was used as the foaming liquid preparation device 3, and the aqueous raw material liquid flow rate and air flow rate were changed as described below. A foaming liquid was prepared.
Foaming liquid preparation device: “Maider made by Taiheiyo Kiko MDN304 type [Horizontal (horizontal rotating shaft type) rotating three-stage slit blade type emulsifying disperser]” rotor (generator) and outer cylinder (jacket) to the following rotor and outer cylinder It replaced and was used as "foaming liquid preparation apparatus 3".
Rotor: a cylinder with a pin with an outer diameter of 130 mm (excluding the pin part), pin height 27.0 mm
Outer cylinder: A cylinder with a pin with an inner diameter of 185 mm (not including the pin part), the height of the pin is 27.0 mm
Protrusion volume ratio: 50%
Cylindrical part length: 100mm
Rotation speed: 2000rpm
Distance between pin in outer cylinder and pin on rotor (C): 0.5mm
Aqueous raw material liquid flow rate 5440ml / min
Air flow rate 2720ml / min
Residence time: 10 seconds Table 1 shows the measurement results of “foaming ratio”, “foam diameter”, and “foaming liquid temperature” in the prepared aqueous foaming liquid.

The results of Examples 1 to 3 and Comparative Examples 1 to 3 contain a film-forming resin suitable for a high-speed rotating foaming machine in a method of producing a foaming liquid by mechanically stirring and mixing air and liquid. It shows that a foaming liquid containing a uniform bubble diameter and containing small bubbles in a stable state can be produced by treating the aqueous raw material liquid with a specific type of foaming machine with a specific residence time.
Then, the aqueous foam solution prepared in the process of each embodiment, those commercially available wood free paper having a basis weight of 104.7 g / m ² (trade name: Marshmallow, manufactured by Oji Paper Co., Ltd.) dried applicator bar on one side of the It was confirmed that a paper base sheet having a foamed resin coating layer excellent in surface smoothness was obtained even when the coating amount was 10 g / m ² later.

  According to the method of the present invention, there is provided a method capable of simply and continuously producing a resin-containing aqueous foam containing a large amount of fine bubbles with a uniform foam diameter in a stable state. By using the liquid as a coating liquid for forming a foamed resin coating layer, various fields are required to form a foamed resin coating layer having a smooth surface state and excellent heat insulation and cushioning properties on the substrate surface. This greatly contributes to the improvement of product quality.

1: Raw material liquid preparation tank 2: Pump 3: Foaming liquid preparation apparatus 4: Cooling jacket 5: Gas storage tank 6: Flow control valve 7a: Inlet side pressure gauge 7b: Outlet side pressure gauge 8: Coater head M: Drive motor S: Outer cylinder (stator)
R: Inner cylinder (rotor)
L: Liquid part G: Gas part C: Distance between projections D1, D1b: Inner diameter D2 of outer cylinder S, D2b: Outer diameter of inner cylinder R

Claims (10)

  An apparatus for preparing an aqueous foamed liquid by mechanically stirring and mixing a mixed fluid composed of an aqueous raw material liquid containing a resin for forming a foamed coating film and a water-insoluble gas, with a fixed protrusion having a cooling function The ratio of the outer diameter (excluding protrusions) of the rotating inner cylinder with protrusions to the inner diameter (excluding protrusions) of the outer cylinder with protrusions and the inner cylinder with protrusions rotating within the outer cylinder with protrusions. Is 75 to 95%, and the volume ratio of all protrusions in the volume between the outer cylinder and the inner cylinder (the volume calculated assuming no protrusions) is 30 to 50%. Preparation equipment.   The aqueous foam according to claim 1, wherein a gap between the protrusions is 0.2 to 3.0 mm when the protrusion of the outer cylinder with protrusions and the protrusion of the inner cylinder with protrusions are closest to each other. Liquid preparation equipment.   The occupied volume ratio of the protrusions in the volume between the outer cylinder and the inner cylinder (the volume calculated assuming that there are no protrusions) is gradually set higher from the inlet side of the mixed fluid toward the outlet side of the aqueous foam liquid. The apparatus for preparing an aqueous foaming liquid according to claim 1 or 2, wherein   A mixed fluid composed of an aqueous raw material liquid containing a foamed coating film-forming resin and a water-insoluble gas is supplied to the aqueous foaming liquid preparation apparatus according to any one of claims 1 to 3, The residence time calculated by dividing the space volume between the outer cylinder with protrusions and the inner cylinder with protrusions by the inflow velocity of the supplied mixed fluid is set to 1.0 to 15 seconds and allowed to pass through the preparation device. A method for preparing an aqueous foaming liquid for forming a foamed resin coating film, characterized by performing foaming treatment.   The aqueous foam liquid for forming a foamed resin coating film according to claim 4, wherein the aqueous raw material liquid containing the resin for forming a foamed coating film is a resin-containing raw material liquid of an aqueous resin system or an aqueous resin emulsion system. Preparation method.   6. The foamed resin according to claim 4, wherein the aqueous raw material liquid containing the foamed coating film-forming resin contains a carboxy-modified styrene / butadiene copolymer latex having a particle diameter of 150 to 250 nm. A method for preparing an aqueous foaming liquid for forming a coating film.   The aqueous raw material liquid containing the foamed coating film-forming resin is an aqueous raw material liquid containing a styrene / butadiene copolymer latex and a polyoxyethylene alkyl ether surfactant. Item 7. A method for preparing an aqueous foaming liquid for forming a foamed resin coating film according to any one of Items 4 to 6.   The diameter of the bubbles in the aqueous foaming liquid that has undergone the foaming treatment by the aqueous foaming liquid preparation device is 1 to 15 µm, and the foaming ratio is adjusted to 1.1 to 2.0. The preparation method of the aqueous | water-based foaming liquid for foaming resin coating film formation in any one.   The aqueous foaming liquid for forming the foamed resin coating film is an aqueous foaming coating liquid for forming a foamed resin coating film layer between the substrate and the thermosensitive coloring layer in the thermal recording paper. The preparation method of the aqueous foaming liquid for foaming resin film formation of description.    The aqueous foam for forming a foamed resin coating film prepared by the method for preparing an aqueous foam according to any one of claims 4 to 9 is applied to the substrate sheet surface as a coating liquid within 5 minutes after the preparation of the aqueous foam. A method for producing a base sheet for a heat-sensitive recording material, wherein the foamed resin layer is formed by coating and drying.

Images