JP2012157806A - Method for producing aqueous foamed liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preparing an aqueous foamed coating liquid for forming a foamed resin coated film.SOLUTION: The method for preparing an aqueous foamed liquid for forming a foamed resin coated film includes passing an aqueous foamed liquid through a cooler for stirring and mixing the aqueous foamed liquid, wherein the aqueous foamed fluid is foamed by mechanically stirring and mixing an aqueous raw material liquid containing a resin for forming a coated film and a non-aqueous gas, and wherein the cooler is provided with: a static mixer with a function of dividing a fluid passing through a tubular body by a plurality of elements fixed and arranged in series within the tubular body, turning the direction of the fluid, and stirring and mixing the fluid with a reversed direction; and a cooling mechanism for cooling the fluid passing through the tubular body from outside the tubular body via a tubular wall of the static mixer.

Description

  The present invention relates to a method for preparing an aqueous foaming liquid containing a resin capable of forming a resin coating film 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 produced 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 obtain a foam coating layer with excellent heat insulation and cushioning properties, it is preferable that the volume ratio of the foam in the foam coating layer is large, and in order to obtain a foam coating layer having a smooth surface, the size of the bubbles is uniform. And it is preferable that the bubble diameter is small. In order to form such a foam coating layer, it is necessary to prepare a foam coating solution having a high volume ratio of bubbles and a small bubble diameter.

  There are chemical methods and mechanical methods for preparing a foaming liquid containing a large amount of bubbles. The chemical foaming method is a method of preparing a foaming liquid by generating a gas in the liquid by a chemical reaction, and the mechanical foaming method is a method of creating a foaming liquid by mechanically stirring and mixing the gas and the liquid. As a method, the mechanical foaming method is preferable because it does not use chemicals, so that the foam coating layer is chemically stable and economical.

JP 05-032052 A Japanese Patent Laid-Open No. 11-043699

  In the mechanical foaming method, a foaming liquid is prepared by mechanically stirring and mixing a gas and a liquid. However, when trying to reduce the bubble diameter in the foaming liquid, a strong shearing force is applied at the gas / liquid mixing part. Need to give. When the shearing force is weak, the bubble diameter does not become small, or foaming does not become uniform. However, when mechanically strong shear is applied, heat is generated due to friction, and the temperature of the foaming liquid rises. In general, the viscosity of solutions and emulsions often decreases with increasing temperature. When the temperature of the foaming liquid rises and the viscosity decreases, foam breakage, foam coalescence, etc. easily occur. For this reason, it is desirable to cool the stirring and mixing part of the mechanical foaming device, but in order to cool the rotating and moving parts such as the stirring rotor, it is necessary to provide a cooling water channel on the rotating shaft and the mechanism is complicated. Therefore, it is general to cool only the outside of the rotary stirring unit. However, in such a cooling method, since the cooling area is limited, the cooling efficiency is not high and sufficient cooling is difficult.

  In order to absorb the heat generated by stirring and mixing, it is possible to cool the liquid to be foamed in advance and then send it to the mechanical foaming device, but this will cause an increase in the viscosity of the liquid due to cooling, alteration due to freezing, etc. There is a fear, and it is difficult to cool below the freezing point with an aqueous solution or aqueous emulsion.

  Therefore, it is possible not only to cool the stirring and mixing unit, but also to install a cooling unit such as a double-pipe heat exchanger downstream of the stirring and mixing unit to cool the foaming liquid. Is easy to flow inside the cooling pipe by plug flow (piston flow), and since it is foaming and has high heat insulation, only the foaming liquid in contact with the pipe wall is cooled, and the foaming liquid flowing in the center part of the pipe is cooled. Not. It is also possible to obtain sufficient cooling by increasing the heat transfer area by thinning or elongating the flow path of the cooling section, but in that case, the arrival time from the stirring and mixing section to the cooling section outlet becomes longer, rather In many cases, bubble breaking and foam coalescence progress. Moreover, the installation of such a heat exchange device has a great demerit in terms of cleaning and maintenance.

  Further, in the mechanical foaming method, when the amount (volume) of bubbles in the foaming liquid is small, for example, a foaming liquid having a ratio of the volume of the foaming liquid (foaming ratio) to the volume of the liquid before foaming is less than 1.1. It is relatively easy to make and it is also relatively easy to reduce the bubble diameter. Devices capable of producing such a foaming liquid are commercially available at low cost as microbubble generators and nanobubble generators. However, when the expansion ratio is low, characteristic effects of bubbles such as cushioning properties and heat insulation properties cannot be expected.

  In order to develop the characteristic effect of bubbles, the amount of bubbles in the foaming liquid is increased, that is, when an attempt is made to increase the mixing ratio of gas to the liquid, the amount of gas introduced into the stirring and mixing part of the foaming device is increased. However, simply increasing the amount of gas introduced will cause the gas and liquid to pass through without being sufficiently stirred and mixed in the stirring and mixing section, and the bubble diameter will not be reduced or uneven foaming will occur. There is a problem that the gas is in a state, the gas and the liquid are separated, and a foaming liquid having a desired foaming ratio and a desired foam diameter cannot be obtained.

Therefore, when producing a foaming liquid having a high expansion ratio, a gas and a liquid pass through the stirring and mixing unit by causing a pressure loss (giving flow path resistance) to the downstream side of the stirring and mixing unit of the foaming apparatus. It is necessary to prevent this from occurring and to perform sufficient stirring and mixing. In general, a commercially available mechanical foaming apparatus is provided with a narrowed portion of the flow path downstream of the stirring and mixing portion in order to cause pressure loss. For example, Aikosha's turbo whip and Mondomix's Mondomix are equipped with a mechanism that generates a pressure loss by using part of the flow path as a rubber tube and constricting the flow path by applying pressure from the outside. ing. In some cases, pressure loss is generated by constricting the flow path with a valve such as a needle valve. However, when a local constriction is provided in the flow path to cause a pressure loss in this way, the pressure of the foaming liquid is abruptly decreased immediately after passing through the constriction. Often increases and breaks or coalesces.
In addition, when the above-mentioned locally constricted portion is provided to generate a desired pressure loss, heat is also generated locally due to friction between the foaming liquid and the foaming liquid-flow path. From the rise in the temperature of the liquid, it accelerates bubble breakage and coalescence of bubbles.

  The present invention has been made in view of the above circumstances, and in a mechanical foaming method for obtaining a foaming liquid by mechanically stirring and mixing a gas and a liquid, the foaming liquid contains a large amount of fine bubbles having a small bubble diameter. It aims at providing the manufacturing method of.

  The present invention that can solve the above-described problems is a fluid that passes through an aqueous foaming treatment liquid obtained by mechanically stirring and mixing an aqueous raw material liquid containing a resin for forming a coating film and a water-insoluble gas and foaming. It is integrated with a static mixer equipped with an element having a stirring and mixing function inside the tubular body, and is cooled by passing through a cooler of the type that cools the internal fluid through the tube wall of the static mixer. Thus, the invention relates to the following method for preparing an aqueous foam for forming a foamed resin coating film, which is based on a method for producing a stable aqueous foam that does not cause foam breakup or foam coalescence.

(1) A plurality of elements in which an aqueous foaming liquid obtained by mechanically stirring and mixing an aqueous raw material liquid containing a resin for forming a coating film and a water-insoluble gas is foamed and fixed in series inside the tube body The fluid passing through the tube through the tube wall of the static mixer having the function of dividing the fluid passing through the tube, changing the direction and reversing the direction and stirring and mixing the fluid A method for preparing an aqueous foaming liquid for forming a foamed resin coating film, characterized in that the mixture is stirred and cooled by passing through a cooler having a cooling mechanism for cooling the tube from the outside.

(2) Stirring / cooling treatment by the cooler allows the foamed aqueous foaming liquid to pass through the static mixer under conditions where pressure loss occurs at a rate of 4 to 50 kPa / cm in the flow direction. The method for preparing an aqueous foaming liquid for forming a foamed resin coating film according to item (1), which is a process of stirring and cooling.

(3) Stirring / cooling treatment by the cooler passes through the foamed aqueous foam liquid under the condition that a pressure loss of 100 to 500 kPa (0.1 to 0.5 MPa) occurs in the static mixer. The method for preparing an aqueous foaming liquid for forming a foamed resin coating film according to (1) or (2), which is a process of stirring and cooling.

(4) Any one of (1) to (3), wherein the aqueous raw material liquid containing the resin for forming a coating film is an aqueous raw material liquid selected from a resin aqueous solution and an aqueous resin emulsion-based resin-containing liquid. A method for preparing an aqueous foaming liquid for forming a foamed resin coating film according to the item.

(5) The diameter of bubbles in the aqueous foamed liquid that has been stirred and cooled after passing through the cooler including the static mixer and the cooling mechanism is 15 μm or less, preferably 1 to 10 μm, and the expansion ratio is The method for preparing an aqueous foaming liquid for forming a foamed resin coating film according to any one of (1) to (4), which is adjusted to exceed 1.1.

(6) The method for preparing an aqueous foaming liquid for forming a foamed resin coating film according to any one of (1) to (5), wherein the water-insoluble gas is air and / or nitrogen.

(7) 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. 6. A method for preparing an aqueous foaming liquid for forming a foamed resin coating film according to any one of items 6).

(8) Applying the aqueous foam liquid for forming a foamed resin coating film prepared by the preparation method described in the above items (1) to (7) to the base sheet surface as a coating liquid, and drying. A base sheet for a heat-sensitive recording material having a formed foamed resin layer.

  ADVANTAGE OF THE INVENTION According to this invention, the method which can produce the resin-containing aqueous | water-based foaming liquid which has a uniform foam diameter and contains a lot of fine bubbles in large quantities at a low cost is possible. Further, the foamed resin coating layer formed by coating the resin-containing aqueous foaming liquid is a foamed resin coating layer having a smooth surface state and excellent heat insulation and cushioning properties. The present invention can be applied to various products that are required to have a layer having excellent heat insulation and cushioning properties, such as an intermediate layer made of a foamed resin layer.

It is a schematic diagram of the apparatus which can implement the preparation method of the aqueous foaming liquid for foaming resin coating film formation of this invention.

Hereinafter, a method for preparing an aqueous foam coating solution for forming a foamed resin coating film of the present invention will be described with reference to the drawings.
FIG. 1 shows a continuous production apparatus capable of carrying out the method for preparing an aqueous foaming liquid for forming a foamed resin coating film of the present invention.

  In the apparatus of FIG. 1, the code | symbol 1 shows the "raw material liquid preparation tank" which prepares the aqueous raw material liquid containing resin for film formation. In the “raw material liquid preparation tank 1”, an aqueous raw material liquid containing a resin for forming a coating film composed of “resin aqueous solution” or “aqueous resin emulsion” containing water and resin at a predetermined ratio is prepared. The prepared aqueous raw material liquid is sent by the “pump 2” to the “foaming treatment tank 3” having the “cooling jacket 4” and supplied from the “gas storage tank 5” through the “flow rate adjusting valve 6”. Aqueous foaming liquid in which bubbles are formed is prepared by mixing together with nitrogen or air and stirring and mixing with a stirrer M.

Next, the aqueous foaming liquid prepared in the foaming treatment tank 3 is installed so as to cover the “static mixer 7” (static mixer) and its outer wall after the introduction pressure is measured by the “inlet side pressure gauge 7a”. It is introduced into a static mixer 7 of a “cooler 8” having a “cooling mechanism 10” composed of a cooling jacket or the like. The numerical value of the pressure loss set in the cooler 8 as a difference between the numerical value of the inlet pressure in the “inlet side pressure gauge 7a” and the numerical value of the outlet side pressure in the “outlet side pressure gauge 7b” of the cooler 8 will be described later. Furthermore, the arrangement state of the plurality of elements installed in the static mixer 7 in the cooler 8 and the pressure loss of the fluid passing through the arrangement state of the plurality of elements are designed to be proportional to the length. It is adjusted by adjusting the length of the stationary mixer 7.
The resin-containing aqueous foamed liquid, which has been further miniaturized at the same time through the cooler 8 and is uniformly cooled to be a stable foamed liquid, is stored in the “aqueous foamed liquid storage tank 9”, and the foamed resin coating layer Used as a coating solution to form

  In the continuous production apparatus of FIG. 1, the temperature of the aqueous raw material liquid prepared in the “raw material liquid preparation tank 1” is kept at a temperature that 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 that the raw material liquid is within a range that does not cause freezing or extreme increase in viscosity that hinders handling in liquid form. It is preferable to cool from the outside of the preparation tank 1.

“Pump 2” that sends an aqueous raw material solution made of a resin aqueous solution or an aqueous resin emulsion prepared in “raw material solution preparation tank 1” to “foaming treatment tank 3”, air, nitrogen gas, etc. from “gas storage tank 5” “ There is no limitation on the type of “flow rate adjusting valve 6” sent to the “foaming treatment tank 3”.
The gas sent from the “gas storage tank 5” by the “flow rate adjusting valve 6” is introduced into the “foaming treatment tank 3” from a supply path different from the supply path of the aqueous raw material liquid in FIG. Can be supplied to the supply path of the aqueous raw material liquid and introduced into the “foaming treatment tank 3” together with the aqueous raw material liquid.

  The “foaming treatment tank 3” disperses and mixes gas such as air as fine bubbles in a resin-containing aqueous raw material liquid by mechanical stirring while continuously supplying gas and liquid in a closed system. It is a device for. For example, a multi-cylindrical continuous foaming machine with slits (a cylindrical rotor with a slit on the side is fitted in the gap between the cylindrical multiple stators with slits on the side, and the rotor rotates at high speed. The resin-containing aqueous raw material liquid and air are fed into the resin-containing aqueous raw material liquid by stirring and mixing the resin-containing liquid and air when passing through the slit. , Double-cylindrical continuous foaming machine (consisting of resin by stirring and mixing the resin-containing aqueous raw material liquid, which is composed of a rotor with a pin and an outer tube with a pin, and rotated into the cylinder at high speed) Disperse-type mixers that shear between the inner blade rotating at high speed and the fixed outer blade can be used.

  The “foaming treatment tank 3” is desirably cooled by installing a “cooling jacket 4” or the like on the outside thereof. When the rotation speed of the stirrer M in the “foaming treatment tank 3” can be set low (about 3000 ppm or less), the cooling efficiency can be increased by cooling the inside of the rotating portion through cooling water.

In the method of the present invention, the rotational speed of the stirrer M in the “foaming treatment tank 3”, the aqueous raw material liquid and air, etc. The size of the 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 aqueous foaming liquid prepared in the “foaming treatment tank 3” which is a closed system is sent to the cooler 8 as it is prepared.

The “cooler 8” includes a static mixer 7 and a cooling mechanism 10 that covers the tube wall.
In the cooler 8, the entire part of the aqueous foaming liquid that passes through the dividing action, the direction changing action, and the direction reversing action on the aqueous foaming liquid by each of the plurality of elements arranged in the static mixer 7 is the cooling mechanism 10. In addition, the air bubbles in contact with the inner wall of the pipe body cooled in (1) are cooled evenly, and the bubbles in the aqueous foaming liquid are further refined by the element so that the bubbles have a uniform diameter.
As the static mixer 7 integrated with the cooling mechanism 10, a stirring mixer having no driving unit of the type known as “static mixer” is used.

  In the method of the present invention, the aqueous foaming liquid introduced into the static mixer 7 in the cooler 8 is introduced into the static mixer of the cooler 8 while maintaining the pressure as prepared in the foaming treatment tank 3. However, the cooler 8 is configured so that the introduced foaming treatment liquid passes through the flow direction at a rate of 4 to 20 kPa / cm and a pressure loss of 0.1 to 0.5 MPa as a whole. The flow path length of the static mixer portion, the shape of the element in the static mixer, the number of elements arranged, etc. are adjusted. The pressure loss of the aqueous foaming liquid that passes while being cooled uniformly in the static mixer varies depending on the flow rate and viscosity of the aqueous foaming liquid. Adjust the flow length of the static mixer of the cooler 8, the shape of the static mixer element, the number of elements, etc., and the cooling temperature so that the aqueous foam can pass through the cooler 8 with pressure loss. To do.

  When the pressure loss in the cooler 8 is set to a value lower than 0.1 MPa as a whole, the “foaming treatment tank 3” directly connected to the cooler 8 allows sufficient mixing of gas and liquid. Accordingly, the aqueous foaming liquid having the foaming ratio required in the cooler 8 cannot be prepared. On the other hand, if the value is set higher than 0.5 MPa, the raw material liquid or gas stays in the “foaming treatment tank 3”, where the temperature rises by receiving severe shear, and cooling of the cooler 8 As a result of an excessive load on the mechanism 10, the aqueous foaming liquid exiting the cooler 8 is likely to be altered, and the required power for feeding the liquid and gas to the “foaming treatment tank 3” increases, which is not preferable.

The range of pressure loss per unit length in the flow direction in the static mixer portion of the cooler 8 is desirably 4 kPa / cm to 40 kPa / cm. If the value is less than 4 kPa / cm 2, the length of the portion of the static mixer necessary to obtain the desired pressure loss is increased, which is not economically preferable, and the time required to pass through the cooler 8 Since it becomes too long and it becomes easy to foam and to unite, it is not preferable.
On the other hand, when the value is larger than 40 kPa / cm, the pressure of the aqueous foaming liquid suddenly decreases when leaving the cooler 8, so that the bubbles in the foaming liquid rapidly expand and the broken bubbles are united. It is not preferable because it often occurs.

  In the cooler 8 used in the method of the present invention, the “static mixer 7” integrated with the cooling mechanism 10 has functions such as dividing the fluid passing therethrough, changing the direction, and reversing the direction. A stirring mixer that does not have a drive unit generally called a “static mixer” is used, in which a plurality of elements are fixedly arranged in a pipe line. Examples of the static mixer that can be used include a mixer of the type used in the manufacture of lightweight soaps described in Patent Document 2. As such a static mixer, a rectangular plate inside a tubular member twisted 180 degrees around its longitudinal axis is used as a minimum unit member, and a plurality of minimum unit members (elements) are alternately turned in different directions. What has the structure arrange | positioned integrally in series so that it may become.

In addition, a combination of notched cones as shown in Japanese Patent Laid-Open No. 5-131126, or a combination of comb-like elements as shown in Japanese Patent Laid-Open No. 2004-195542, which is rotated It is also possible to use a static mixer that divides and mixes fluids without accompanying.
There are types of static mixers in which liquid is stirred and mixed by installing a disk (baffle plate, partition) or the like with holes in the flow path so as to be orthogonal to the flow of the fluid. Due to the local narrowing, the coalescence of the bubbles is likely to occur, and even after washing after use, a residue is likely to be generated inside, which is not suitable for the method of the present invention.
As the static mixer element, various materials such as metal and resin can be used, but stainless steel or resin material is preferably used from the viewpoint of chemical resistance.

  In the cooler 8, the portion of the static mixer 7 that is cooled by the cooling mechanism 10 does not necessarily match the length of the cooling mechanism 10 portion. Prepare a static mixer in which the flow path length of the part where the cooling mechanism is arranged is long and the pressure loss value per unit length is known, and the appropriate pressure loss as described above The method of increasing / decreasing the length of the static mixer is simple.

  The “cooling mechanism 10” of the cooler 8 is not particularly limited. A normal cooling mechanism such as water cooling, air cooling, or cooling with a Peltier element can be employed. The static mixer part is installed in the cooling tank, or the cooling jacket 10 is installed outside the static mixer, and heat is exchanged by bringing the coolant into contact with the outer wall of the static mixer 7. The cooling method is efficient.

  The cooler 8 having the static mixer 7 is not necessarily a single unit. A plurality of coolers may be installed in parallel to the flow path of the foaming liquid so as to obtain a desired pressure loss and cooling effect. Moreover, it is good also as a structure which can increase / decrease the number of connections so that a several pressure cooler may be connected in series and a desired pressure loss and a cooling effect may be acquired. If the cooling in the cooler 8 is insufficient, the temperature of the aqueous foam liquid to be prepared becomes high, and bubbles break and coalesce with time, which is not preferable.

A foamed resin coating layer can be formed on a sheet using an aqueous foaming liquid prepared 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 foaming 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>
An aqueous raw material liquid (solid content concentration of 31%) prepared in the raw material liquid preparation tank 1 of FIG. 1 at a flow rate of 100 mL / min is supplied to a “foaming treatment tank 3” (double cylindrical continuous foaming machine) by a pump 2. : It consists of an 80 mm diameter rotor with a pin and a 100 mm diameter outer tube with a pin, and was sent to a rotation speed of 2000 rpm. Simultaneously with the aqueous raw material liquid, air whose flow rate was adjusted to 20 mL / min in terms of atmospheric pressure by the flow rate control valve 6 was sent from the “gas storage tank 5” to the “foaming treatment tank 3”. “Cooler 8” (channel tube inner diameter 8 mm) equipped with “static mixer 7” (static mixer manufactured by Noritake Co., Ltd., diameter 8 mm, length 25 cm) was prepared as the aqueous foaming treatment liquid prepared in “foaming tank 3”. ). Cooling water at 10 ° C. was passed through the “cooling mechanism 10” (cooling jacket) outside the cooler 8 to cool the foamed liquid in the static mixer. The pressure loss per unit length of the aqueous foaming liquid passing through the cooler 8 was 20 kPa / cm, and the overall pressure loss was 0.5 MPa. When the specific gravity of the aqueous foaming liquid sent out from the cooler 8 was measured and the expansion ratio was determined, the expansion ratio was 1.2. 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.

[Raw material composition]
Water-dispersible polyurethane resin (trade name: Adekabon titer HUX-381, manufactured by Asahi Denka Kogyo Co., Ltd.) 100 parts Foam stabilizer: Higher fatty acid ammonium salt (trade name: F-1) 5 parts Thickener: Carboxymethylcellulose ( (Product name: AG gum, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 3 parts 31 parts were taken from the mixture of the above components, and water was added to make 100 parts as a raw material solution.

[Production of foamed resin-coated sheet]
The aqueous foamed liquid prepared by the above method has a coating weight of 10 g after drying with an applicator bar on one side of a high-quality paper (trade name: Marshmallow, manufactured by Oji Paper Co., Ltd.) having a basis weight of 104.7 g / m ^2. / M ² was applied. A paper base sheet having a foamed resin coating layer excellent in surface smoothness was obtained.

<Example 2>
In the method of Example 1, the length of the static mixer 7 in the cooler 8 of FIG. 1 is 5 cm, and the pressure loss of the foaming liquid passing through the cooler 8 is 20 kPa / cm per unit length, which is 0 in total. An aqueous foaming liquid was prepared in the same manner as in Example 1 except that the pressure was 1 MPa.
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, the length of the static mixer 7 in the cooler 8 of FIG. 1 is 12.5 cm, and the pressure loss of the foaming liquid passing through the cooler 8 is 40 kPa / cm per unit length. An aqueous foaming liquid was prepared in the same manner as in Example 1 except that a static mixer of 0.5 MPa was incorporated.
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, an aqueous foaming liquid was prepared in the same manner as in Example 1 except that the static mixer 7 was not inserted into the cooler 8 of FIG.

<Comparative Example 2>
In the method of Example 1, an aqueous foaming liquid was prepared in the same manner as in Example 1 except that cooling by passing cooling water was not performed in the cooler 8 of FIG.
Table 1 shows the measurement results of “foaming ratio”, “foam diameter”, and “foaming liquid temperature” in the prepared aqueous foaming liquid.

<Comparative Example 3>
The aqueous foaming liquid was prepared in the same manner as in Example 1 except that the length of the static mixer used in Example 1 was 4.0 cm, and the pressure loss of the cooler 8 was 20 kPa / cm per unit length and 80 KPa in total. Prepared.
Table 1 shows the measurement results of “foaming ratio”, “foam diameter”, and “foaming liquid temperature” in the prepared aqueous foaming liquid.

<Comparative Example 4>
In the method of Example 1, the aqueous solution was the same as Example 1 except that a static mixer in which the pressure loss of the foaming liquid passing through the cooler 8 was 100 kPa / cm per unit length and the total was 0.5 MPa was incorporated. A foaming liquid was prepared.
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 4 are the downstream side of the foam processing apparatus that mechanically stirs and mixes air and liquid in the method of producing the foamed liquid by mechanically stirring and mixing air and liquid. In addition, by providing a cooler equipped with a static mixer and uniformly cooling while controlling the pressure loss value of the foaming liquid passing through to a predetermined value, bubbles are uniformly contained and contain small bubbles in a stable state. It shows that a foaming liquid can be produced.

  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 treatment tank 4: Cooling jacket 5: Gas storage tank 6: Flow control valve 7: Static mixer 7a: Inlet side pressure gauge 7b: Outlet side pressure gauge 8: Cooler 9 : Aqueous foam storage tank 10: Cooling mechanism

Claims (7)

  An aqueous foamed liquid obtained by mechanically stirring and mixing an aqueous raw material liquid containing a resin for forming a coating film and a water-insoluble gas is foamed by a plurality of elements fixedly arranged in series inside the tubular body. The fluid passing through the tubular body is separated from the outside of the tubular body through a stationary mixer having a function of stirring and mixing the fluid by dividing the fluid passing through the fluid, changing the direction and reversing the direction, and the tube wall of the stationary mixer. A method for preparing an aqueous foaming liquid for forming a foamed resin coating film, characterized in that the mixture is stirred and cooled by passing through a cooler having a cooling mechanism for cooling from the outside.   Stirring / cooling treatment by the cooler is performed by passing the foamed aqueous foam liquid through the static mixer at a rate of 4 to 50 kPa / cm in the flow direction and stirring and cooling. The method for preparing an aqueous foaming liquid for forming a foamed resin coating film according to claim 1, wherein   The stirring / cooling process by the cooler is a process of stirring and cooling the stationary foam mixer by passing the foamed aqueous foaming liquid under a condition that causes a pressure loss of 100 to 500 kPa. Or the preparation method of the aqueous | water-based foaming liquid for foaming resin coating-film formation of 2.   The foamed resin coating according to any one of claims 1 to 3, wherein the aqueous raw material liquid containing the coating film-forming resin is an aqueous raw material liquid selected from a resin-containing liquid of an aqueous resin system and an aqueous resin emulsion system. A method for preparing an aqueous foaming liquid for film formation.   The diameter of bubbles in the aqueous foamed liquid that has been stirred and cooled through the cooler including the static mixer and the cooling mechanism is 15 μm or less, and the foaming ratio is adjusted to more than 1.1. The preparation method of the aqueous | water-based foaming liquid for foaming resin coating-film formation of any one of Claims 1-4 characterized by the above-mentioned.   The said water-insoluble gas is air and / or nitrogen, The preparation method of the aqueous | water-based foaming liquid for foaming resin coating film formation of any one of Claims 1-5. 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. A method for preparing an aqueous foaming liquid for forming a foamed resin coating film according to the item.

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