Transparent physical gel and its manufacturing method

Abstract

To obtain a transparent physical gel when dispersing clay in water and to propose a novel physical gel which can be used in various fields using a thixotropic nature of the gel.SOLUTION: Provided is a transparent physical gel which is formed by dispersing clay minerals having a particle diameter of 10 to 100 nm in water in a volume fraction (φ) in a range of 0.001 to 0.01 and in a state of a salt concentration of 0.005 [M] or less, and which has a transmitted light intensity (%) of 80% or higher when the physical gel is filled in a rectangular parallelepiped quartz cell, which has a square cross section with one side of 10 mm, and transmittance of light with a beam diameter of 0.5 mm and a wavelength of 632.8 nm is measured.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a transparent physical gel having thixotropy and a method for producing the same, and more particularly to a transparent physical gel made of a liquid in which clay particles are dispersed in water, and a method for producing the same. [Background technology]

[0002] Gels prepared by dispersing known clays (clay minerals, etc.) in water are generally observed to be cloudy due to diffuse reflection from the clay particles. Clay-based physical gels exhibit excellent thixotropy, so if transparent physical gels could be produced, their range of applications would be greatly expanded, enabling their use in a variety of fields.

[0003] The present inventor has previously proposed a technique for imparting thixotropy to paint as a simple method for preventing dripping when applying a dye solution for purposes such as decorating walls, etc., in which the fluidity of the paint is improved by mechanical stirring during application, and the viscosity increases after application to the surface of the object to be coated, reducing the fluidity of the paint and suppressing dripping. Typical materials for imparting thixotropy are clays such as saponite, hectorite, and stevensite.

[0004] Other proposed paints include those containing 0.1% by weight or more of natural hectorite clay and 0.5 to 15% by weight of phosphonate based on the weight of the clay (Patent Document 1). This proposal claims that the use of natural hectorite is superior to the use of synthetic hectorite in terms of balance with fluidity, suspension control, stability, and the like.

[0005] However, these prior art documents do not state that a transparent physical gel is obtained or that the gel becomes transparent when clay is dispersed in water, etc. This is because simply dissolving clay in water does not make the gel transparent; in other words, it is generally observed that the gel becomes cloudy due to diffuse reflection from the clay particles.

[0006] For example, there is a proposal for an aqueous gel (Patent Document 2) that can be considered transparent if it is 6 mm or less in thickness, but this gel originally uses an organic thickener such as xanthan gum as a base material, to which clay such as aluminosilicate or smectite is added (as an inorganic thickener), and is not a proposal for a transparent gel whose main component is clay. Furthermore, because the thickness used is thin, it is likely to appear cloudy if used in a thick product.

[0007] None of the above proposals have investigated the production of a transparent gel by simply combining clay and water, and generally, each component is simply weighed out in a predetermined ratio and dispersed in water to produce a gel. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-154717 [Patent Document 2] Special Publication No. 2017-532532 Summary of the Invention [Problem to be solved by the invention]

[0009] The object of the present invention is to obtain a transparent physical gel when clay is dispersed in water, and to propose a novel physical gel that can be used in a variety of fields by utilizing the thixotropy of the gel. [Means for solving the problem]

[0010] The transparent physical gel of the present invention is prepared by dispersing clay minerals with particle diameters of 10 to 100 nm in water at a volume fraction (φ) of 0.001 to 0.01 and a salt concentration of 0.005 [M] or less. When the physical gel is filled into a rectangular quartz cell with a square cross section of 10 mm on each side (hence, an optical path length of 10 mm) and the transmittance of light with a beam diameter of 0.5 mm and a wavelength of 632.8 nm is measured, the transmitted light intensity (%) is 80% or more. Note that the M stands for mol / L, and refers to the salt concentration when used as a physical gel, not the salt concentration of the water before the clay mineral is dispersed, but the salt concentration when used as a physical gel.

[0011] When layered silicate minerals such as clay minerals are dispersed in water, the interlayer space becomes negatively charged and the edges of the layers become positively charged, resulting in electrostatic bonds, forming a house-of-cards structure. The force that forms this structure creates resistance, which generates elasticity and forms a physical gel. On the other hand, when a water-soluble metal salt is added to an aqueous gel composition formed from an aqueous dispersion of layered silicate minerals, a uniform house-of-cards structure is not formed, and aggregation and precipitation occur, resulting in either no gel or a sol-like gel. Therefore, in the present invention, the salt concentration must be below a predetermined concentration. This is because the characteristics of the physical gel formed depend on the overall salt concentration after mixing.

[0012] The clay mineral is one or more selected from the group consisting of fluorine-modified hectorite, hectorite, and stevensite, which are suitable for expressing and controlling thixotropy, are highly safe substances that are used in cosmetics as viscosity modifiers and dispersants, and can maintain transparency when made into an aqueous gel.

[0013] Furthermore, the method for producing a physical gel of the present invention is characterized by comprising the steps of: dispersing the clay mineral in water with a volume fraction (φ) of 0.001 to 0.01 and a salt concentration of 0.005 M or less to obtain a dispersion; adding 10 to 20 g of ion exchange resin or ion exchange resin directly in a mesh bag to the dispersion in an amount of 10 to 20 g per 100 mL of the dispersion; and shaking the container containing the dispersion periodically or intermittently (every few hours to a dozen hours) to liquefy the dispersion, and repeating this process for 24 hours to a week. In the first step, it is preferable to disperse a small amount of clay mineral in water in advance to improve the dispersibility of the clay mineral, and then gradually increasing the amount of clay mineral added. [Effects of the Invention]

[0014] The transparent physical gel of the present invention is prepared from highly safe clay minerals, and the gel is transparent when viewed over a certain volume. Therefore, other objects (e.g., miniature submarines or fish models) can be placed inside the transparent gel and used as a three-dimensional display. In other words, the physical gel of the present invention becomes liquid when subjected to an appropriate external force, making it easy to propel objects independently (using a built-in motor, for example) or to move objects from the outside. Furthermore, when the self-propelling force or external force is cut off, the surrounding area gels in that position and state, allowing the object to remain floating in water or on the water surface.

[0015] This allows the built-in motor to be started and stopped repeatedly at appropriate intervals, and only moved when the object is to be viewed by those around as a three-dimensional display, thereby extending the life of the built-in battery, or allowing the object to be used for viewing even when not in motion. [Brief explanation of the drawings]

[0016] [Figure 1] Figure 1 shows photographs of the degree of cloudiness depending on the salt concentration when sodium chloride was added to the transparent physical gel obtained in Example 1 so that the salt concentrations in the gel were 0.005 [M], 0.01 [M], 0.05 [M], and 0.1 [M], respectively, from the left. [Figure 2] FIG. 2 is a graph showing the relationship between the transmitted light intensity when salt is gradually added to the transparent physical gel measured in Example 2. [Figure 3] FIG. 3 is a graph showing the relationship between the transmitted light intensity when salt is gradually added to the transparent physical gel measured in Example 3. [Figure 4] FIG. 4 is a diagram showing the state when five white plastic balls are placed into the transparent physical gel of the present invention obtained in Example 2 and placed at predetermined positions within the physical gel using tweezers. DETAILED DESCRIPTION OF THE INVENTION

[0017] The transparent physical gel of the present invention is prepared by dispersing clay minerals with particle diameters of 10 to 100 nm in water at a volume fraction (φ) of 0.001 to 0.01 and a salt concentration of 0.005 M or less. When the physical gel is filled into a rectangular quartz cell with a square cross section measuring 10 mm on each side and the transmittance of light with a wavelength of 632.8 nm and a beam diameter of 0.5 mm is measured, the transmitted light intensity (%) is 80% or more. Because this transparent physical gel contains clay minerals, it has so-called thixotropy (a property in which, although it initially appears solid, its viscosity decreases and it becomes liquid when subjected to continued shear stress such as stirring or shaking, and then returns to its original viscosity when the stress is removed).

[0018] The objective of the present invention is to make the physical gel transparent. Therefore, the salt concentration after mixing is important. As mentioned above, the house-of-cards structure formed by the clay minerals is strongly influenced by the metal salts in the gel, which affects the dispersion state of the clay minerals.

[0019] Conventionally, when dispersing clay minerals in water, the salt concentration in the water to be used (before dispersion) has been taken into consideration. However, even if the salt in the water before dispersion is sufficiently removed in advance through an ion exchange resin, the clay mineral to be mixed generally contains salt as an impurity, so it cannot be said that the salt concentration of the dispersion liquid has been strictly controlled.

[0020] In the present invention, to remove salts believed to be originally present in clay minerals, the clay mineral is dispersed in water (ion-exchanged water or ultrapure water) at the predetermined volume fraction, and then an ion-exchange resin is introduced into the dispersion, either directly or in a mesh bag. The introduction of the resin into a mesh bag facilitates the removal of salts to a predetermined concentration or below, and the ion-exchange resin can then be easily removed from the dispersion. This process removes as much salt as possible from the dispersion (particularly, but not limited to, salts derived from clay minerals) (hereinafter referred to simply as "desalting treatment"). Note that, in this specification, "dispersion" refers to the state before the desalting treatment of the present invention, and "transparent physical gel" refers to the state after the desalting treatment. While there is no significant difference in thixotropy between the two, the transparent physical gel of the present invention is one that exhibits a transmitted light intensity (%) of 80% or less at a wavelength of 632.8 nm.

[0021] To perform efficient desalination, after adding the ion exchange resin, the container containing the dispersion is vibrated periodically or intermittently (every few to 10-odd hours) to liquefy the dispersion, and this process is continued for 24 hours to a week. This is because the dispersion remains liquid (due to thixotropy) while an external force (such as shear force) is applied, and such stirring and vibration can improve the desalination effect of the ion exchange resin. "Periodic" refers to vibration at a preset time, and "intermittent" refers to vibration at irregular intervals (with intervals of several to 10-odd hours).

[0022] The container can be vibrated using a shaking incubator such as that used for culturing microorganisms, a rotary shaker, or by manually moving the container to vibrate it, etc. A stirring bar or agitator may also be used, but since only the rotating part of the stirring bar or stirring blade will liquefy and it is difficult to liquefy the entire dispersion, it is desirable to stir the entire dispersion by moving the rotation position of the stirring blade, etc.

[0023] The desalination treatment using ion exchange resin is preferably carried out for a period of 24 hours to one week. Even if the treatment is carried out for a longer period, the desalination effect is not significantly improved, and the transmitted light intensity remains at 80% or more. On the other hand, a transparent physical gel can be obtained even if the treatment is carried out for a shorter period than 24 hours, as long as there is almost no salt in the original clay mineral. Furthermore, the treatment temperature is around room temperature, and there is no need to heat or cool the gel.

[0024] Examples of ion exchange resins that can be used in the present invention include AG501-X8(D) (manufactured by Bio-Rad) and Amberlite (manufactured by Organo Corporation). Among these, Amberlite (manufactured by Organo Corporation) is preferred in terms of versatility, price, ion exchange capacity, etc.

[0025] The amount of ion exchange resin to be added varies depending on the type of resin used, but is generally about 10 to 20 g per 100 mL of dispersion (physical gel). If the amount is less than this, desalination takes longer, and if the amount is more than this, it becomes difficult to separate the resin after desalination, especially when the resin is added directly.

[0026] Clay minerals used in the present invention include natural clay, synthetic clay, and organized clay, and particularly, at least one selected from the group consisting of clays containing silicon and magnesium as main components, and organized clays is preferred.

[0027] Clays primarily composed of silicon and magnesium refer to clays in which the metal components of the metal oxides constituting the clay are primarily composed of silicon and magnesium, and may contain other metal oxides (aluminum, iron, etc.) as secondary components. Clays primarily composed of silicon and magnesium are not particularly limited, and known clays can be used as appropriate. By using clays primarily composed of silicon and magnesium, it is possible to increase dispersibility due to the small particle size. Furthermore, clays having a smectite structure are preferred as such clays primarily composed of silicon and magnesium, in terms of availability.

[0028] Examples of such clays containing silicon and magnesium as the main components include stevensite, hectorite, saponite, and talc. Among these, it is more preferable to use hectorite and fluorine-modified hectorite from the viewpoint of the transparency of the gel.

[0029] When the clay mineral concentration (volume fraction) is low, the shear modulus tends to decrease rapidly as the salt concentration increases. On the other hand, when the clay mineral concentration is high, the effect is relatively small even when the salt concentration increases. This indicates that even if the clay minerals that form the house-of-cards structure are lost due to aggregation in the presence of salt, there is still enough capacity in the solution to compensate for the loss.

[0030] Since the objective of the present invention is to form a transparent physical gel, the amount of clay mineral must be determined taking into consideration the balance between the shear modulus of the gel and not affecting transparency. Specifically, it is preferable to use clay mineral in a volume fraction (φ) range of 0.001 to 0.01. Here, the volume fraction is the value obtained by dividing the volume of the clay mineral before dispersion by the volume of the dispersion liquid.

[0031] Since thixotropy is a characteristic of the transparent physical gel of the present invention, if the volume fraction of the clay mineral is lower than 0.001, the shear modulus of the physical gel becomes too low, making it difficult to capture and maintain an object placed in the gel in a stationary state when used as a three-dimensional display. On the other hand, if the volume fraction is higher than 0.01, the salt concentration in the clay mineral-derived dispersion becomes high, requiring a long time for desalination treatment using an ion exchange resin, and in some cases, making it difficult to obtain a transparent gel. Therefore, as mentioned above, a volume fraction (φ) in the range of 0.001 to 0.01 is appropriate.

[0032] The water used to disperse the clay mineral is preferably pure water that has been desalted by ion exchange or the like, and specifically has an electrical conductivity of about 0.01 to 1 mS / m. Of course, even if the electrical conductivity is higher than the above, this is not a big problem because salts can be removed by desalting, but since the salt concentration must ultimately be reduced, water with a high salt concentration from the beginning is not used.

[0033] The particle size of the clay mineral used in the present invention is preferably in the range of 10 to 100 nm. This is because it is generally easy to obtain and has excellent handling and operability (for example, it is less likely to scatter when measuring). In addition, when dispersing in water, if the particles are too fine, they will form clumps and become difficult to disperse, and if the particles are too large, they will be difficult to disperse uniformly.

[0034] As mentioned above, the desalination process takes place over a period of 24 hours to a week, with the salt concentration after the process being 0.005 M or less. Even if the concentration is above this level, a transparent physical gel can be formed if the volume fraction of clay minerals is small. However, the shear modulus of the gel is low, which places restrictions on the materials that can be trapped within the physical gel. In other words, when attempting to hold an object still in a predetermined position, objects with a specific gravity heavier than water tend to sink, expelling the gel, while lighter objects tend to float.

[0035] The transparency after desalination treatment according to the present invention is evaluated by placing the physical gel in a rectangular quartz cell with a square cross section of 10 mm on each side (hence, the optical path length is 10 mm), and measuring the transmittance of light with a beam diameter of 0.5 mm and a wavelength of 632.8 nm. The transmitted light intensity (%) is 80% or more. The transmitted light intensity can be easily measured using, for example, a photoelectric colorimeter CANA-3030 (manufactured by Tokyo Koden Co., Ltd.).

[0036] In order to clarify the present invention more specifically, some examples will be given below.

[0037] Example 1 0.25 g of fluorine-modified hectorite (Kunimine Industries Co., Ltd.) was dispersed in 10 g of ion-exchanged water (electrical conductivity 0.01 mS / m) to obtain dispersion (a). The volume fraction was 0.01. The salt concentration of dispersion (a) was approximately 0.05 [M].

[0038] 0.3 g of AG501-X8(D) (Bio-Rad) ion exchange resin was directly added to the dispersion (a), and the container was shaken intermittently (about 1 minute every 2 to 10 hours), and this was repeated for 72 hours to reduce the salt concentration to below the detection limit (0.001 [M]). Then, the ion exchange was removed using a clean mesh sheet.

[0039] Sodium chloride was then added to the transparent physical gels obtained in this way so that the salt concentrations in the gels were 0.005 M, 0.01 M, 0.05 M, and 0.1 M, respectively, and the gels were stirred thoroughly. The states after standing were compared. The results are shown in Figure 1.

[0040] As can be seen from Figure 1, when the salt concentration in the gel reaches 0.05 [M] or higher, the gel becomes clearly cloudy.

[0041] Example 2 Fluorine-modified hectorite (Kunimine Industries Co., Ltd.) was weighed out in amounts of 0.06 g, 0.13 g, and 0.25 g, respectively, and dispersed in 10 g of ion-exchanged water (electrical conductivity 0.01 mS / m) to obtain dispersions with volume fractions (φ) of 0.0025, 0.005, and 0.01, respectively.

[0042] 0.3 g of AG501-X8(D) (Bio-Rad) ion exchange resin was directly added to each dispersion, and the container was shaken intermittently (approximately 1 minute every 2 to 10 hours) for 72 hours, until the salt concentration reached the detection limit (0.001 [M]). The ion exchange resin was then removed using a clean mesh sheet.

[0043] Sodium chloride was added to the transparent physical gels thus obtained in the same manner as in Example 1 so that the salt concentrations in each gel were 0.005 [M], 0.01 [M], 0.05 [M], and 0.1 [M], respectively, and the gels were stirred well and allowed to stand.

[0044] Each physical gel was then placed in a rectangular quartz cell with a square cross section measuring 10 mm on a side, and the transmitted light intensity of light with a beam diameter of 0.5 mm and a wavelength of 632.8 nm was measured using the measurement system of a photoelectric colorimeter CANA-3030 (manufactured by Tokyo Koden Co., Ltd.).

[0045] The results are shown in the graph (Figure 2).

[0046] From the graph (Figure 2), it can be seen that in the case of fluorine-modified hectorite, if the volume fraction is 0.005 or less and the salt concentration is 0.005 [M] or less, the transmitted light intensity is 80% or more. Note that when the volume fraction is 0.005, the transmitted light intensity of the dispersion (before desalting treatment) is 2-3%.

[0047] Example 3 0.25 g of each of the clay minerals fluorine-modified hectorite (Kunimine Industries Co., Ltd.), hectorite (Kunimine Industries Co., Ltd.), and stevensite (Kunimine Industries Co., Ltd.) were weighed and dispersed in 10 g of ion-exchanged water (electrical conductivity 0.0001 mS / m) to obtain dispersions. The volume fraction (φ) was 0.005 for all dispersions.

[0048] 0.3 g of AG501-X8(D) (Bio-Rad) ion exchange resin was directly added to each dispersion, and the container was periodically shaken (for example, every few hours to a dozen hours for about 1 minute) for 72 hours to stir the solution, and the salt concentration was reduced to below the detection limit (0.001 [M]). The ion exchange resin was then removed using a clean mesh sheet.

[0049] Sodium chloride was added to the transparent physical gels thus obtained in the same manner as in Example 1 so that the salt concentrations in each gel were 0.005 [M], 0.01 [M], 0.05 [M], and 0.1 [M], respectively, and the gels were stirred well and allowed to stand.

[0050] Each physical gel was then placed in a rectangular quartz cell with a square cross section measuring 10 mm on a side, and the transmitted light intensity of light with a beam diameter of 0.5 mm and a wavelength of 632.8 nm was measured using the measurement system of a photoelectric colorimeter CANA-3030 (manufactured by Tokyo Koden Co., Ltd.).

[0051] The results are shown in the graph (Figure 3).

[0052] The graph (Figure 3) shows that, among the three clay minerals, fluorine-modified hectorite produced the most transparent gel. At a volume fraction of 0.005, the transmitted light intensity of the hectorite dispersion (before desalting) was 2-3%.

[0053] Example 4 Figure 4 shows a photograph of the transparent physical gel of the present invention obtained in Example 2 (fluorine-modified hectorite was used as the clay mineral, and the volume fraction (φ) was 0.01), in which five white plastic balls were placed in designated positions within the physical gel using tweezers, and then the tweezers were removed.

[0054] Figure 4 shows photographs of two spheres (upper left), three spheres (lower left), and one sphere (upper right) floating in the gel while the other spheres are submerged, and the photograph on the lower right shows a photograph of all the spheres submerged. As shown in these figures, it is clear that within the transparent physical gel of the present invention, an object can be held in a predetermined position and its position can be changed. [Industrial Applicability]

[0055] The transparent physical gel of the present invention has thixotropy and transparency, and can be exhibited as a three-dimensional display or as art. Furthermore, because it is prepared from highly safe clay minerals, it can be used as a toy for children, allowing them to enjoy free arrangements, for example, placing models of goldfish in an aquarium.

Claims

[Claim 1] A physical gel is obtained by dispersing fluorine-modified hectorite having a particle diameter of 10 to 100 nm in water at a volume fraction (φ) of 0.0025 to 0.005 and at a salt concentration of 0.005 [M] or less, and the physical gel is filled into a rectangular quartz cell having a square cross section with one side measuring 10 mm, and when the transmittance of light having a beam diameter of 0.5 mm and a wavelength of 632.8 nm is measured, the transmitted light intensity (%) is 80% or more.

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