Method for producing resin dispersion liquid

Abstract

Provided is a method for producing a resin dispersion liquid that contains at least water and a water-insoluble resin, the method including step [b] and step [c]. A mixed liquid obtained following the completion of step [b] has a viscosity of 4.0×105 mPa·s or less. The content ratio (mass ratio) of the water relative to the water-insoluble resin in the mixed liquid is 2.0 or less. Step [b]: a first addition step for adding and mixing, at atmospheric pressure, water to the water-insoluble resin which is in a liquid state at a temperature of 73ºC or lower. Step [c]: a second addition step for adding and mixing water to the mixed liquid obtained by step [b].

Description

Method for producing resin dispersion

[0001] The present invention relates to a method for producing a resin dispersion.

[0002] In recent years, there has been an increasing demand for inks for inkjet printers. Inkjet printers have various advantages, including the ease of full-color printing, low noise, ability to produce high-resolution images at low cost, high-speed printing, the ability to print on curved surfaces as well as flat surfaces, and the ability to easily print on large areas. As a result, inkjet printers are not limited to personal use, but have also been rapidly gaining popularity in recent years as commercial inkjet printers for signage, window films, posters, car wrapping, wallpaper, and the like.

[0003] Conventional printing inks for commercial inkjet printers include aqueous inks in which a pigment is dispersed or dissolved in an aqueous medium; solvent inks in which a pigment is dispersed or dissolved in an organic solvent medium; and solvent-free UV inks in which a pigment is dispersed in a solvent-free ultraviolet-curable monomer.

[0004] Of these, water-based inks are highly environmentally friendly, but the water resistance, solvent resistance, and hardness of the coating film may be insufficient compared to solvent inks and solvent-free UV inks.

[0005] One solution to the above problems with aqueous inks is latex ink, which is made by dispersing a water-insoluble or poorly soluble binder resin in particulate form in an aqueous medium. Latex inks have superior coating film hardness compared to inks in which the binder resin is dissolved in water. However, latex inks generally require additives such as organic solvents and surfactants, as well as special stirring methods, to uniformly disperse the inherently water-insoluble or poorly soluble resin in water.

[0006] Patent Documents 1 and 2 disclose a method of dispersing a resin in an organic solvent and then removing the organic solvent by vacuum distillation to obtain a dispersion of resin particles. However, this method involves discharging the organic solvent, which raises concerns about its environmental compatibility.

[0007] Patent Document 3 discloses a method for producing an aqueous emulsion by applying pressure under temperature conditions exceeding 100° C. However, stirring and mixing at temperatures exceeding 100° C., which is the boiling point of water under normal pressure, requires equipment that can withstand high pressures, and there are also concerns about safety during production.

[0008] Patent Document 4 discloses a method in which urethane acrylate and polypentaerythritol polyacrylate are mixed with a photoradical polymerization initiator at 80°C, and water is added at 50°C. This method does not require the use of organic solvents or surfactants, and allows emulsions to be obtained under mild conditions where water does not boil at normal pressure. However, Patent Document 4 does not clearly describe the physical properties of the substances formed during the preparation of the dispersion or the specific steps of the dispersion process. Furthermore, Patent Document 4 does not describe the method of adding water, whether it should be added all at once or in portions.

[0009] JP 2022-150039 A JP 2022-150040 A JP 2008-106262 A JP 2013-199602 A

[0010] An object of the present invention is to provide a method for producing a resin dispersion by dispersing a water-insoluble resin in water, which method can produce a resin dispersion with few coarse particles, suitable as a raw material for inkjet inks, under mild conditions.

[0011] The present inventors have found that a resin dispersion containing few coarse particles can be obtained under mild conditions by including a step of adding water to and mixing a water-insoluble resin in a liquid state that has been melted at or below a specific temperature, repeating this water addition and mixing step two or more times, adjusting the viscosity of the system after the first water addition and mixing step to a specific value or less, and adjusting the content ratio (mass ratio) of water to the water-insoluble resin in the system to a specific value or less.

[0012] [1] A method for producing a resin dispersion containing at least water and a water-insoluble resin, comprising the following steps [b] and [c], wherein the viscosity of the mixture obtained after completion of the following step [b] is 4.0 × 10 ５a viscosity of 1000 psi or less and a mass ratio (mass ratio) of the water to the water-insoluble resin in the mixed solution of 2.0 or less, wherein the viscosity of the water-insoluble resin is 1000 psi or less and the mass ratio of the water to the water-insoluble resin in the mixed solution is 2.0 or less, and ...

[0013] [2] The method for producing a resin dispersion according to [1], which includes the following step [a] before the step [b]: Step [a]: Melting the water-insoluble resin

[0014] [3] The method for producing a resin dispersion according to [1] or [2], wherein the content of the surfactant in the resin dispersion is 0.1 mass % or less relative to the total mass of the resin dispersion.

[0015] [4] The method for producing a resin dispersion according to any one of [1] to [3], wherein the content of the organic solvent in the resin dispersion is 1 mass % or less with respect to the total mass of the resin dispersion.

[0016] [5] The method for producing a resin dispersion according to any one of [1] to [4], wherein the water-insoluble resin contains a hydrophilic structure and a hydrophobic structure.

[0017] [6] The method for producing a resin dispersion according to [5], wherein the hydrophilic structure is a structure derived from polyalkylene glycol.

[0018] [7] The method for producing a resin dispersion according to any one of [1] to [6], wherein in the step [b], the water-insoluble resin is in a liquid state at 69°C or less.

[0019] [8] The viscosity of the mixture after the step [b] is 1.0 × 10 ５ [8] The method for producing a resin dispersion according to any one of [1] to [7], wherein the viscosity is 0.05 mPa·s or less.

[0020] [9] The method for producing a resin dispersion according to any one of [1] to [8], wherein the content ratio (mass ratio) of the water to the water-insoluble resin in the mixed solution after completion of the step [b] is 1.5 or less.

[0021]

[10] The method for producing a resin dispersion according to any one of [1] to [9], further comprising a step [d] of adding an additive.

[0022]

[11] The method for producing a resin dispersion according to

[10] , wherein the additive added in the step [d] is encapsulated in particles of the water-insoluble resin in the resin dispersion.

[0023]

[12] The method for producing a resin dispersion according to

[10] or

[11] , wherein the additive includes at least one selected from the group consisting of a polymerization initiator, a sensitizer, and a polymerizable monomer.

[0024] According to the present invention, it is possible to produce a resin dispersion containing few coarse particles and in which a water-insoluble resin is well dispersed, even under mild conditions. The resin dispersion produced by the present invention is a resin dispersion in which a water-insoluble resin is well dispersed, and can be suitably used as a raw material for inkjet inks.

[0025] An embodiment of the present invention will be described below, but the present invention is not limited to this embodiment.

[0026] In the present invention, when the expression "X to Y" (X and Y are any numbers) is used, it includes the intention of "X or more and Y or less", as well as "preferably greater than X" and "preferably smaller than Y", unless otherwise specified. Furthermore, in the present invention, when the expression "X or more" (X is any number) or "Y or less" (Y is any number) is used, it also includes the intention of "preferably greater than X" or "preferably less than Y".

[0027] <Method for producing resin dispersion> The method for producing a resin dispersion of the present invention is a method for producing a resin dispersion containing at least water and a water-insoluble resin, and includes the following step [b] and the following step [c], wherein the viscosity of the mixed liquid obtained after completion of the following step [b] is 4.0 × 10 ５ The method is characterized in that the viscosity of the water-insoluble resin in the mixed solution is 73° C. or less, and the content (mass ratio) of the water to the water-insoluble resin in the mixed solution is 2.0 or less. Step [b]: A first addition step of adding water to the water-insoluble resin in a liquid state at 73° C. or less under atmospheric pressure and mixing the water-insoluble resin. Step [c]: A second addition step of adding water to the mixed solution obtained in step [b] and mixing the water-insoluble resin.

[0028] In the present invention, the water added in the steps [b] and [c] may be tap water, demineralized water, or ultrapure water. Among these, demineralized water (ion-exchanged water) is preferred as the water to be added from the viewpoints of both ease of availability and high purity.

[0029] The method for producing a resin dispersion of the present invention may optionally include other treatments or steps as long as it includes at least two water addition and mixing steps [b] and [c]. For example, in addition to steps [a] and [d] described below, it may also include a filtration step for filtering the produced resin dispersion.

[0030] In the present invention, a "process" may or may not be performed in a continuous production line. Furthermore, the processing in one process may be performed intermittently, and in this case, the processing may be performed intermittently by leaving a time gap, changing the equipment, or changing the location. Furthermore, the process may be performed in a continuous production line together with other processes. In other words, multiple processes may be performed in the same equipment.

[0031] The method for producing a resin dispersion of the present invention can obtain a resin dispersion containing few coarse particles and in which a water-insoluble resin is well dispersed, even under mild conditions. The mechanism by which this effect is achieved is not clear, but is presumed to be as follows.

[0032] By adding water in portions while maintaining the temperature of the water-insoluble resin at 73° C. or less, the dispersion passes through a co-continuous phase in which the water-insoluble resin and water form continuous phases. Furthermore, by adding water stepwise in a state in which the co-continuous phase has been formed, it is presumed that the water-insoluble resin phase in the co-continuous phase is uniformly cut by the water, the particle size is appropriately reduced, and a resin dispersion free of coarse particles is obtained.

[0033] [Step [a]] The method for producing a resin dispersion of the present invention may further include step [a]. In step [a], the water-insoluble resin is melted. Step [a] is preferably performed before step [b] described below.

[0034] The means or device for melting the water-insoluble resin is not particularly limited, but examples thereof include an oven, a band heater, a hot plate, a water bath, an oil bath, and a jacketed reaction vessel.

[0035] The temperature at which the water-insoluble resin is melted is preferably 73°C or lower, more preferably 71°C or lower, and even more preferably 69°C or lower. On the other hand, this temperature is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 65°C or higher. By keeping the temperature within the above range, the viscosity of the mixed liquid obtained in step [b] can be kept low, and aggregation of the water-insoluble resin at high temperatures can be suppressed. Furthermore, safety in production is improved.

[0036] Step [a] may be carried out with stirring. Preferred stirring means, stirring devices, and rotation speeds during stirring are the same as those in step [b] described below.

[0037] [Step [b]] Step [b] is a first addition step in which water is added to and mixed with the water-insoluble resin in a liquid state at 73°C or less under atmospheric pressure.

[0038] The water-insoluble resin may be in a liquid state beforehand, or may be in a solid state beforehand and then melted at 73°C or less to form a liquid. Here, "liquid state" means that the water-insoluble resin has fluidity. "Solid state" means that the water-insoluble resin does not exhibit fluidity and can maintain its shape. The suitable temperature for the water-insoluble resin in a liquid state in step [b] is usually 5°C or higher, preferably 10°C or higher, and more preferably 20°C or higher. On the other hand, the upper limit of this temperature is 73°C or lower, but is preferably 71°C or lower, and more preferably 69°C or lower.

[0039] When the method for producing a resin dispersion of the present invention includes the step [a], the suitable temperature of the water-insoluble resin in a liquid state is the same as the melting temperature range of the water-insoluble resin in the step [a].

[0040] The means or device for adding water is not particularly limited. Examples include a burette, a dropper, a pump, etc. Among these, a pump is preferable from the viewpoint of industrialization.

[0041] The water addition rate is preferably 100 g / min or more from the viewpoints of improving work efficiency and suppressing the formation of an undesired high-viscosity composition. On the other hand, there is no particular upper limit to the water addition rate, and it can be appropriately determined depending on the performance of the equipment for producing the resin dispersion. In step [b], the entire amount of water to be added may be added all at once, or may be added continuously or in portions at the above-mentioned addition rate.

[0042] The stirring means or stirring device for mixing is not particularly limited. Examples include paddle-type, helical-type, anchor-type, turbine-type, and crescent-type stirring blades, pencil mixers, homogenizers, etc. Among these, crescent-type or helical-type stirring blades are preferred because they are easy to prepare.

[0043] The rotation speed during stirring is preferably 500 rpm or less, more preferably 300 rpm or less. When the rotation speed is equal to or less than the upper limit, no special equipment is required, scale-up is easy, and safety in production is improved. On the other hand, there is no particular restriction on the lower limit of the rotation speed, and a rotation speed that allows the water-insoluble resin and water to be sufficiently mixed can be selected depending on the stirring method and the size of the stirring container.

[0044] In step [b], water is added to and mixed with the water-insoluble resin under atmospheric pressure (0.1 MPa). By performing step [b] under atmospheric pressure, special equipment such as reduced pressure equipment or high pressure equipment is not required, scale-up is easy, and production safety is improved.

[0045] In the present invention, "under atmospheric pressure" encompasses a range of 0.1 MPa - 0.02 Pa to 0.1 MPa + 0.02 Pa. In the present invention, the pressure conditions for step [a] other than step [b] and steps [c] and [d] described below are not particularly limited, but it is preferable to carry out these steps under atmospheric pressure, as in step [b].

[0046] The viscosity of the system after the step [b] (here, "system" refers to the mixed liquid obtained by adding water to the water-insoluble resin and mixing in the step [b]) was 4.0 × 10 ５By setting the viscosity to the upper limit or less, the mixed solution of the water-insoluble resin and water produced in the middle of the step [b] can be easily dispersed uniformly in the water added in the subsequent step [c]. ５ It is preferable that the viscosity is 5.0×10 mPa·s or less. ４ On the other hand, from the viewpoint of forming a bicontinuous phase, the viscosity is more preferably 1.0×10 ３ It is preferable that the viscosity is 1.0×10 mPa·s or more. ４ The viscosity of the system is more preferably 100 mPa·s or more. The method for measuring the viscosity of the system is as described in the Examples section below.

[0047] The content ratio (mass ratio) of water to water-insoluble resin in the system after completion of step [b] is 2.0 or less. By setting this content ratio to the upper limit or less, the water-insoluble resin and water form a bicontinuous phase. The content ratio is preferably 1.75 or less, more preferably 1.5 or less. On the other hand, the content ratio is preferably 0.5 or more, more preferably 0.7 or more.

[0048] The step [b] is preferably carried out under temperature conditions that maintain the melting temperature of the water-insoluble resin in a liquid state. For this purpose, the water to be added may be heated.

[0049] [Step [c]] Step [c] is a second addition step in which water is added to and mixed with the mixed liquid obtained in the step [b].

[0050] In the method for producing a resin dispersion of the present invention, by including steps [b] and [c], the step of adding water and mixing is essentially repeated at least twice. This allows a resin dispersion with fewer coarse particles to be obtained via a bicontinuous phase in which the water-insoluble resin and water form continuous phases. From the viewpoint of obtaining a resin dispersion with fewer coarse particles, step [c] is preferably repeated two or more times, more preferably three or more times. There is no particular upper limit on the number of times step [c] is repeated, but from the viewpoint of production efficiency, it is preferably 10 or less times.

[0051] The amount of water added in step [c] varies depending on the application of the resulting resin dispersion, but is preferably an amount such that the content ratio (mass ratio) of water to the water-insoluble resin in the mixed liquid (resin dispersion) obtained after completion of step [c] is 1.5 or more. This content ratio is more preferably 2.0 or more, even more preferably 2.5 or more, and particularly preferably 3.0 or more. On the other hand, the content ratio is preferably 9.0 or less, more preferably 7.0 or less, even more preferably 6.0 or less, and particularly preferably 5.0 or less. The amount of water added in step [c] is preferably an amount such that the solids concentration of the resin dispersion of the present invention obtained through step [c] is the preferred solids concentration described below. If the content ratio is above the above lower limit, the storage stability of the resin dispersion is improved. If the content ratio is below the above upper limit, various additives can be added to the resin dispersion of the present invention, facilitating formulation design when preparing inks, etc.

[0052] When step [c] is performed multiple times, the amount of water added to achieve the above content ratio is preferably calculated by dividing the amount by the number of times step [c] is repeated. However, the amount of water added may be varied for each repetition, for example, by adding more water in the earlier stages and less in the later stages.

[0053] The stirring apparatus and conditions used for adding water and mixing in step [c] are the same as those in step [b]. The temperature conditions at the end of step [c] may be slightly lower than the temperature conditions in step [b], for example, about 2 to 10°C lower.

[0054] [Step [d]] The method for producing a resin dispersion of the present invention may further include a step [d] of adding an additive.

[0055] The additive to be added is not particularly limited. Examples of the additive include additives described below, preferably any one or more selected from the polymerization initiators, sensitizers, and polymerizable monomers described below. One type of additive may be added, or two or more types may be added. When adding the additive, the total amount to be added may be added all at once, or may be added in several divided portions. When adding in divided portions, the number of divisions is not particularly limited.

[0056] The additive added in step [d] is preferably encapsulated in the water-insoluble resin particles in the resin dispersion. For example, the additive can be encapsulated in the water-insoluble resin particles by mixing the water-insoluble resin in a liquid state with the additive and then performing step [b], or by mixing the additive between multiple steps [c]. That is, step [d] of adding the additive may be performed by adding the additive to the water-insoluble resin in a liquid state during or after step [a], or by adding the additive to a mixture of the water-insoluble resin and water during step [b], or may be performed during step [c].

[0057] <Resin Dispersion> The resin dispersion obtained by the method for producing a resin dispersion of the present invention (hereinafter, sometimes referred to as the "resin dispersion of the present invention") is suitably used as a material for latex ink, but is not limited thereto. The resin dispersion of the present invention can also be used, for example, as a toner, an adhesive, a coating material, etc.

[0058] In the resin dispersion of the present invention, the water-insoluble resin preferably exists as particles.

[0059] The light intensity-average particle diameter of the water-insoluble resin particles in the resin dispersion is preferably 1 μm or less. When the light intensity-average particle diameter is equal to or less than the upper limit, ejection properties are improved when ejecting ink containing the resin dispersion in an inkjet printer, which is preferable. The light intensity-average particle diameter can be measured, for example, with a particle size measuring device using a dynamic light scattering method.

[0060] The resin dispersion of the present invention can be used to prepare an ink by adding a colorant, which will be described later. The colorant to be added may be one color or two or more colors. By optionally adding two or more colorants, the color of the ink can be adjusted to a desired color.

[0061] The method for preparing the resin dispersion of the present invention into an ink is not particularly limited, but an example is a method in which a resin dispersion and a dispersion in which a colorant such as a pigment is dispersed in an aqueous medium (hereinafter, sometimes referred to as a "colorant dispersion") are separately prepared, and then the resin dispersion is mixed with other additives, an organic solvent, and the colorant dispersion. The colorant dispersion can be prepared by adding a colorant such as a pigment to a solvent such as water and mixing them.

[0062] From the viewpoint of facilitating formulation design when producing an ink, the solids concentration, which is the concentration of components other than the solvent in the resin dispersion of the present invention, is preferably 5% by mass or more, more preferably 10% by mass or more, and particularly preferably 15% by mass or more. There is no particular upper limit to this solids concentration, but from the viewpoint of improving the storage stability of the resin dispersion, it is preferably 35% by mass or less, and particularly preferably 30% by mass or less.

[0063] From the viewpoints of ease of handling and storage stability, the concentration of the colorant such as a pigment in the colorant dispersion is preferably 5% by mass or more, more preferably 10% by mass or more, and is preferably 40% by mass or less, more preferably 35% by mass or less. As the colorant dispersion, a commercially available product may be used as it is.

[0064] The viscosity of the ink produced from the resin dispersion of the present invention can be adjusted as desired depending on the application and usage form. When the ink is used in an inkjet printer, the viscosity at 25°C is preferably 25 mPa·s or less, more preferably 20 mPa·s or less, and even more preferably 15 mPa·s or less. The lower limit of the ink viscosity is not particularly limited, but is preferably 1 mPa·s or more, and more preferably 2 mPa·s or more.

[0065] [Water-insoluble resin] In the present invention, a water-insoluble resin is used. One water-insoluble resin may be used alone, or two or more water-insoluble resins having different resin compositions, physical properties, etc. may be mixed and used.

[0066] Here, "water-insoluble resin" is defined as follows: 1 g of resin is added to 50 g of demineralized water. A magnetic stirrer is added and the mixture is stirred at 300 rpm for 10 minutes. After stirring, if any undissolved resin can be visually confirmed, the resin is "water-insoluble." If no undissolved resin can be visually confirmed, the particle size distribution of the aqueous solution or aqueous dispersion is measured using a particle size distribution meter (e.g., NANOTRAC WAVE II, manufactured by MicrotracBEL, etc.), and if a distribution in the particle size range of 10 nm or more is observed, the resin is deemed "water-insoluble." If no distribution is observed, the resin is deemed not "water-insoluble." Furthermore, the term "resin" used here refers to an oligomer or polymer having a structure in which multiple structural units are bonded, and does not include so-called monomers.

[0067] The water-insoluble resin used in the present invention is a resin that becomes liquid at a temperature of 73° C. or less. From the viewpoint of workability, it is preferable that the water-insoluble resin used in the present invention is in a liquid state at the suitable temperature for the water-insoluble resin in the step [b].

[0068] The ionicity of the water-insoluble resin used in the present invention is not particularly limited, but is preferably nonionic. Here, nonionic means, for example, that the resin is composed of ether bonds or hydroxyl groups that do not ionize in water. On the other hand, ionic (anionic, cationic, or amphoteric) means, for example, that the resin has a carboxy group or an amino group that can ionize in water. More specifically, anionic resins include, for example, resins containing carboxy groups.

[0069] The water-insoluble resin is preferably a resin containing a hydrophilic structure and a hydrophobic structure. A water-insoluble resin containing a hydrophilic structure and a hydrophobic structure has excellent dispersion stability in a resin dispersion. Here, examples of the hydrophilic structure include a structure derived from the compound (C') described below. The hydrophilic structure is preferably a structure derived from polyalkylene glycol, as this structure has excellent water dispersibility.

[0070] The type of water-insoluble resin is not particularly limited, and examples thereof include known water-insoluble oligomers or polymers. More specifically, examples thereof include urethane resins, ester resins, acrylic resins, and hydrophilic portion-modified resins thereof. Among these, urethane resins modified with polyoxyalkylene are easily dispersed in water and are therefore suitable for use.

[0071] The water-insoluble resin preferably further contains a polymerizable group. When the water-insoluble resin contains a polymerizable group, when the resin dispersion is made into an ink, the polymerizable group in the ink coating film can be polymerized, thereby improving the degree of curing of the coating film.

[0072] Examples of such polymerizable groups include (meth)acryloyl groups, vinyl groups, and vinyl ether groups. Among them, (meth)acryloyl groups are preferred from the viewpoint of ease of radical polymerization. In the present invention, "(meth)acrylate" means acrylate or methacrylate. The same applies to "(meth)acryloyl." The number of polymerizable groups in one molecule of the resin is preferably 2 or more, more preferably 3 or more, and on the other hand, preferably 15 or less.

[0073] The water-insoluble resin is preferably an ultraviolet-curable oligomer or polymer, more preferably an ultraviolet-curable oligomer, from the viewpoint of being present as particles in water.

[0074] As described above, examples of the ultraviolet-curable oligomer that is modified by a hydrophilic moiety and contains a polymerizable group include compounds produced by reacting the polyisocyanate compound (A) described below with the following compounds (B') and (C'). However, the examples below are not intended to limit the scope of the invention. Compound (B'): A compound that contains a polymerizable unsaturated bond and can bond with the polyisocyanate compound (A). Compound (C'): A water-soluble compound that can bond with the polyisocyanate compound (A).

[0075] The compound produced by reacting the polyisocyanate compound (A), the compound (B') and the compound (C') will be described in more detail below.

[0076] Examples of the structure of compound (B') that can bond to polyisocyanate compound (A) include a hydroxyl group, a carboxyl group, and an amino group. Examples of the polymerizable unsaturated bond include a carbon-carbon double bond and a carbon-carbon triple bond, with a carbon-carbon double bond being preferred. More specific examples include carbon-carbon double bonds derived from a vinyl group, a (meth)acryloyl group, or the like.

[0077] The water-soluble compound in compound (C') includes a water-soluble polymer. Specific examples of the water-soluble compound in compound (C') include polyglycerin, polyhydroxy(meth)acrylate, polyamine, quaternary aminated polystyrene, sulfonated polystyrene, polyether, polyalkylene glycol, etc. Among these, polyglycerin, polyhydroxy(meth)acrylate, and polyalkylene glycol are preferred, and polyalkylene glycol is particularly preferred. Each of these water-soluble compounds may be a copolymer. Compound (C') has the structure of such a water-soluble compound and a structure capable of bonding to polyisocyanate compound (A). Here, the "structure capable of bonding to polyisocyanate compound (A)" is the same as that of compound (B') described above.

[0078] The polyisocyanate compound (A), the compound (B') and the compound (C') may additionally have other structures.

[0079] The weight-average molecular weight of the water-insoluble resin, as determined by gel permeation chromatography (GPC) in terms of polystyrene, is preferably 500 or more, more preferably 1,000 or more, from the viewpoint of dispersing the resin as particles in water rather than dissolving it in water. In addition, from the viewpoint of stably maintaining the resin as particles, the weight-average molecular weight of the water-insoluble resin is preferably 100,000 or less, more preferably 50,000 or less.

[0080] [Solvent] The resin dispersion of the present invention may contain a solvent other than water, but preferably does not substantially contain any solvent. That is, the resin dispersion of the present invention preferably does not substantially contain any organic solvent. By substantially not containing any organic solvent, the safety to the human body and the environmental compatibility of the production method are improved.

[0081] Here, "substantially free of solvents other than water (organic solvents)" means that the mass ratio of solvents other than water (organic solvents) is 1% or less relative to the total mass of the resin dispersion of the present invention. That is, the content of organic solvents in the resin dispersion of the present invention is preferably 1% or less by mass, more preferably 0.5% or less by mass, relative to the total mass of the resin dispersion.

[0082] [Additives] The resin dispersion of the present invention may contain additives.

[0083] When an additive is contained, the additive may be present alone in the resin dispersion, or the additive may be encapsulated in particles of a water-insoluble resin (hereinafter, sometimes referred to as "resin particles") in the resin dispersion. From the viewpoint of preventing aggregation of the resin particles and the additive, it is preferable that the additive be encapsulated in the resin particles in the resin dispersion.

[0084] The additives are not particularly limited, and examples thereof include known additives such as a polymerization initiator, a sensitizer, a polymerizable monomer, a polymerizable polymer other than the water-insoluble resin, a non-polymerizable polymer other than the water-insoluble resin, a colorant, silica, metal particles, an antiseptic, an antifungal agent, an antirust agent, and a surfactant.

[0085] Among these, it is preferable to add one or more of a polymerization initiator, a sensitizer, and a polymerizable monomer, since this improves the curability of the coating film when made into an ink, and it is more preferable to add at least a polymerization initiator.

[0086] The polymerization initiator may be a polymerization initiator that generates radicals, cations, or anions when exposed to light or heat. The polymerization initiator is preferably encapsulated in resin particles in the resin dispersion.

[0087] Examples of the polymerization initiator that generates radicals when exposed to light include aromatic ketones, acylphosphine oxide compounds, aromatic onium salt compounds, organic peroxides, thio compounds (thioxanthone compounds, thiophenyl group-containing compounds), α-aminoalkylphenone compounds, hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon-halogen bond, and alkylamine compounds.

[0088] Examples of the polymerization initiator that generates cations when exposed to light include halonium salts, sulfonium salts, phosphonium salts, and ammonium salts.

[0089] Examples of the polymerization initiator that generates radicals when heated include azo compounds and organic peroxides.

[0090] These polymerization initiators may be used alone or in combination of two or more.

[0091] When a sensitizer is added, the added sensitizer is preferably encapsulated in resin particles in the resin dispersion, and more preferably encapsulated together with a polymerization initiator and / or a polymerizable monomer. By encapsulating the sensitizer in the resin particles together with a polymerization initiator and / or a polymerizable monomer, the sensitizer in the system absorbs active energy rays upon ultraviolet irradiation and becomes excited, and by coming into contact with the polymerization initiator, the decomposition of the polymerization initiator is promoted, thereby enabling a curing reaction with higher sensitivity.

[0092] Examples of sensitizers that can be used include aliphatic amines, amines having an aromatic group, and cyclic amine compounds such as piperidine; alkoxyanthracene compounds, urea compounds such as o-tolylthiourea; sulfur compounds such as sodium diethylthiophosphate and soluble salts of aromatic sulfinic acids; nitrile compounds such as N,N'-disubstituted-p-aminobenzonitrile; phosphorus compounds such as tri-n-butylphosphine and sodium diethyldithiophosphate; Michler's ketone, N-nitrosohydroxylamine derivatives, oxazolidine compounds, tetrahydro-1,3-oxazine compounds; and nitrogen compounds such as condensates of formaldehyde or acetaldehyde with diamines.

[0093] These sensitizers may be used alone or in combination of two or more.

[0094] When a polymerizable monomer is added, the added polymerizable monomer is preferably encapsulated in resin particles in the resin dispersion, and more preferably encapsulated together with a polymerization initiator and / or a sensitizer. By encapsulating the polymerizable monomer in resin particles together with a polymerization initiator and / or a sensitizer, it is expected that the curability of the coating film when made into an ink can be further improved.

[0095] The polymerizable monomer may be, for example, a radical polymerizable monomer. The radical polymerizable monomer is not particularly limited as long as it has one or more radical polymerizable groups in the molecule. The number of radical polymerizable groups in the molecule is preferably 2 or more, more preferably 3 or more, and on the other hand, preferably 15 or less.

[0096] Examples of the radically polymerizable group possessed by the radically polymerizable monomer include a (meth)acryloyl group, a vinyl group, a vinyl ether group, etc. Among these, a (meth)acryloyl group is preferred from the viewpoint of ease of radical polymerization.

[0097] The radical polymerizable compound may be used alone or in combination of two or more kinds.

[0098] The polymeric or non-polymeric polymer used as an additive is a polymer other than the above-mentioned water-insoluble resin, and is a polymer that is in a solid state at 73° C., or is water-soluble, or has both of these properties.

[0099] When a polymerizable or non-polymerizable polymer is added, the added polymerizable or non-polymerizable polymer is preferably encapsulated in resin particles in the resin dispersion. The polymerizable or non-polymerizable polymer is not particularly limited, but examples thereof include polyvinyl alcohol resin, polyalkylene glycol resin, olefin resin, acrylic resin, methacrylic resin, vinyl chloride resin, polycarbonate resin, polyester resin, polyamide resin, polyacetal resin, polystyrene resin, polyvinyl acetate resin, polyurethane resin, and polytetrafluoroethylene resin.

[0100] When two or more of these polymerizable or non-polymerizable polymers are used, the particles may be core-shell particles in which one polymer is encapsulated within the other, or particles having a sea-island structure in which one polymer is distributed in the form of islands within the other.

[0101] When the resin dispersion of the present invention contains a surfactant, any of silicone surfactants, fluorine surfactants, amphoteric surfactants, nonionic surfactants, and anionic surfactants can be used as the surfactant.When a surfactant is contained, the surfactant may be present alone in the resin dispersion, or may be encapsulated in resin particles in the resin dispersion.In addition, the above-mentioned water-insoluble resin is not included in the surfactant.

[0102] However, among additives, it is preferable that the resin dispersion of the present invention is substantially free of surfactants. Here, "substantially free of surfactants" means that the mass ratio of surfactants relative to the total mass of the resin dispersion is 0.1% or less. That is, the content of surfactants in the resin dispersion of the present invention is preferably 0.1% or less by mass, more preferably 0.05% or less by mass, relative to the total mass of the resin dispersion. Since the resin dispersion of the present invention is substantially free of surfactants, the production method is improved in terms of safety to the human body, environmental compatibility, and simplicity.

[0103] The content of the additive encapsulated in the resin particles in the resin dispersion relative to the entire resin dispersion is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less. By having the content of the additive encapsulated in the resin particles be equal to or less than the above upper limit, it is possible to prevent the encapsulated additive from leaking out of the resin particles over time, thereby preventing a decrease in storage stability. Furthermore, the content of the additive relative to the water-insoluble resin in the resin dispersion of the present invention is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0104] [Uses] The resin dispersion of the present invention can be suitably used mainly as a material for ink, particularly for printing ink for inkjet printers. Inks produced from the resin dispersion of the present invention are water-based and therefore have excellent environmental and safety properties. Furthermore, the cured products and printed products formed have excellent water resistance and solvent resistance while satisfying the required performance in a well-balanced manner.

[0105] When the resin dispersion of the present invention is used as an ink, it has the advantage that it can print images having high image quality and excellent cured film performance on various substrates with high productivity, and therefore can be used in various applications such as posters, road signs, signboards, billboards, various outdoor and indoor display boards, building materials (surface materials for exteriors, interiors, walls, floors, ceilings, windows, etc.), exteriors of vehicles, etc. (automobiles, trains, aircraft, etc.), surface materials for furniture, office automation equipment, etc., printed paper materials, textiles, etc.

[0106] An embodiment of the present invention will be described below, although the present invention is not limited to this embodiment.

[0107] [Preparation of Water-Insoluble Resin 1] 0.4 mol of hexamethylene diisocyanate trimer, 0.8 mol of dipentaerythritol pentaacrylate, and 0.4 mol of polyethylene glycol monoallyl ether were reacted to produce Water-Insoluble Resin 1 (nonionic UV-curable oligomer, weight average molecular weight 2,200). This Water-Insoluble Resin 1 becomes liquid at 39°C.

[0108] [Preparation of Resin Dispersion 1] Step [a]: 1 part by mass of the water-insoluble resin 1 obtained above and 0.01 parts by mass of GENOPOL Tx-2 manufactured by RAHN as a polymerization initiator were mixed in a jacketed stirring vessel equipped with a stirring blade, stirring at 50 rpm at 68 ° C. Step [b]: Next, 0.84 parts by mass of ion-exchanged water at 60 ° C. was added while stirring at 200 rpm while maintaining the stirring vessel at 68 ° C. (addition rate: about 200 to 350 g / min) and continued mixing for 2 hours. Step [c]: Then, while lowering the temperature to 63 ° C., 0.84 parts by mass of ion-exchanged water at 60 ° C. was added in four portions while stirring at 200 rpm (total addition amount: 3.36 parts by mass, addition rate: about 200 to 350 g / min). Thereafter, the mixture was filtered through a polypropylene mesh with 106 μm openings to obtain Resin Dispersion 1. Note that the above steps [a] to [c] were all carried out under atmospheric pressure.

[0109] [Preparation of Resin Dispersions 2 to 9] Resin dispersions 2 to 9 were obtained in the same manner as for resin dispersion 1, except that the temperature conditions of step [a] (the temperature conditions of this step [a] are equal to the temperature conditions of step [b]), the temperature conditions at the end of step [c], the number of repetitions of step [c], the viscosity of the system after the end of step [b], and the content ratio (mass ratio) of the water to the water-insoluble resin in the system (referred to as "water / water-insoluble resin ratio" in Table 1) were changed as shown in Table 1.

[0110] The amount of water added in each step [b] and step [c] was 4.2 parts by mass in total. The viscosity of the system after step [b] was measured as follows.

[0111] (Viscosity of the system at the end of step [b]) A viscosity measurement sample was separately prepared to reproduce the mixture mass ratio of the water-insoluble resin 1, the polymerization initiator (Tx-2), and water in the system at the end of step [b]. Since the viscosity of the system at the end of step [b] depends on the mixture mass ratio of the system and the temperature of the system, the viscosity of the measurement sample at a predetermined temperature corresponds to the viscosity of the system at the end of step [b].

[0112] [Measurement of Measurement Sample 1] (Reproduction of Resin Dispersions 1, 3, 6, and 8) A mixture of water-insoluble resin 1, polymerization initiator (Tx-2), and water (water-insoluble resin:Tx-2:water=1:0.01:0.84 (mass ratio)) was mixed at 68°C with stirring, continued stirring for 2 hours, and then cooled to room temperature (25°C) for use.

[0113] [Measurement of Measurement Sample 2] (Reproduction of Resin Dispersions 2 and 5) A mixture of water-insoluble resin 1 and water (water-insoluble resin:water=1:0.84 (mass ratio)) was mixed under stirring at 68°C, continued to stir for 2 hours, and then cooled to room temperature (25°C) for use.

[0114] [Measurement of Measurement Sample 3] (Reproduction of Resin Dispersion 4) A mixture of water-insoluble resin 1, polymerization initiator (Tx-2), and water (water-insoluble resin:Tx-2:water=1:0.01:1.4 (mass ratio)) was mixed at 68°C under stirring, continued stirring for 2 hours, and then cooled to room temperature (25°C) and used.

[0115] [Measurement of Measurement Sample 4] (Reproduction of Resin Dispersion 7) A mixture of water-insoluble resin 1, polymerization initiator (Tx-2), and water (water-insoluble resin:Tx-2:water = 1:0.01:4.2 (mass ratio)) was mixed with stirring at 68°C, stirred for 2 hours, and then cooled to room temperature (25°C) for use. [Measurement of Measurement Sample 5] (Reproduction of Resin Dispersion 9) A mixture of water-insoluble resin 1, polymerization initiator (Tx-2), and water (water-insoluble resin:Tx-2:water = 1:0.01:2.1 (mass ratio)) was mixed with stirring at 68°C, stirred for 2 hours, and then cooled to room temperature (25°C) for use.

[0116] The viscosity of the measurement samples was measured using a rheometer MCR302 (manufactured by Anton Paar) with a 25 mm diameter parallel plate as a jig, a measurement gap of 0.5 mm, and a shear rate of 0.1 / s. A temperature sweep viscosity plot was created by measuring the viscosity while heating at a rate of 2°C / min, and the viscosity at the temperature when water was added in step [b] was calculated. The viscosity of measurement samples 4 and 5 could not be measured because the system was not homogenized.

[0117] [Examples 1 to 4, Comparative Examples 1 to 5] The obtained resin dispersions 1 to 9 were evaluated for the presence or absence of water-insoluble resin residues upon mesh filtration (referred to as "presence or absence of water-insoluble resin residues" in Table 1), particle size distribution, and turbidity as follows. The evaluation results are shown in Table 1.

[0118] (Presence or absence of water-insoluble resin residue upon mesh filtration) The obtained resin dispersions 1 to 9 were each filtered through a mesh with a mesh opening of 106 μm, and the presence or absence of water-insoluble resin residue was visually confirmed. ◯ (good): No residue. × (poor): Residue was present.

[0119] (Particle size distribution) The particle size distribution of the obtained resin dispersions 1 to 9 was measured. The measurement was carried out by diluting each resin dispersion four times using a zeta potential / particle size / molecular weight measurement system ELSZ-2000ZS (manufactured by Otsuka Electronics Co., Ltd.). It was confirmed whether or not a particle size distribution was observed in the region where the particle size exceeded 1 μm, as follows: ◯ (good): No particle size distribution was observed in the region where the particle size exceeded 1 μm. × (poor): A particle size distribution was observed in the region where the particle size exceeded 1 μm.

[0120] (Turbidity) The turbidity of the obtained resin dispersions 1 to 9 was measured. For the measurement, a turbidity meter HI 93703 (manufactured by Hanna Instruments) was used, and the measured turbidity values ​​were evaluated according to the following criteria. In the present invention, S or A was considered a pass, and B or C was considered a fail. By measuring the turbidity, it is possible to compare the state of the number and size of coarse particles that can be visually recognized. When the turbidity is less than 200, preferably less than 100, it can be confirmed that the particle size is appropriately small and a dispersion with little coarse particles mixed in has been obtained. S: Turbidity less than 100 A: Turbidity 100 or more but less than 200 B: Turbidity 200 or more but less than 400 C: Turbidity 400 or more

[0121]

[0122] Table 1 reveals the following: The method comprises two or more water addition and mixing steps, namely, a first addition step [b] in which water is added to and mixed with a water-insoluble resin in a liquid state at 73°C or less under atmospheric pressure, and a second addition step [c] in which water is added to and mixed with the mixed liquid obtained in step [b], and the viscosity of the system after step (b) is 4.0 x 10 ５ When the viscosity is 0.05 mPa·s or less and the content ratio (mass ratio) of water to water-insoluble resin in the system is 2.0 or less, the particle size becomes appropriately small after production is completed, and a resin dispersion liquid containing few coarse particles is obtained.

[0123] In contrast, the resin dispersions of the comparative examples, which do not satisfy any of the above conditions, are inferior in any of the water-insoluble resin residue, turbidity, and particle size distribution, and a resin dispersion having an appropriately small particle size and little coarse particle contamination cannot be obtained.

[0124] Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention. This application is based on Japanese Patent Application No. 2023-193089, filed on November 13, 2023, and is incorporated by reference in its entirety.

Claims

1. A method for producing a resin dispersion containing at least water and a water-insoluble resin, comprising the steps [b] and [c] below, wherein the viscosity of the mixture obtained after the step [b] is 4.0×10 ５ and a content ratio (mass ratio) of the water to the water-insoluble resin in the mixed solution is 2.0 or less. Step [b]: A first addition step of adding water to the water-insoluble resin in a liquid state of 73° C. or less under atmospheric pressure and mixing the water. Step [c]: A second addition step of adding water to the mixed solution obtained in step [b] and mixing the water.

2. The method for producing a resin dispersion according to claim 1, comprising the following step [a] prior to the step [b]: a melting step of melting the water-insoluble resin.

3. A method for producing a resin dispersion according to claim 1 or 2, wherein the content of the surfactant in the resin dispersion is 0.1 mass % or less based on the total mass of the resin dispersion.

4. A method for producing a resin dispersion according to claim 1 or 2, wherein the content of the organic solvent in the resin dispersion is 1 mass % or less based on the total mass of the resin dispersion.

5. The method for producing a resin dispersion according to claim 1 or 2, wherein the water-insoluble resin contains a hydrophilic structure and a hydrophobic structure.

6. The method for producing a resin dispersion according to claim 5, wherein the hydrophilic structure is a structure derived from a polyalkylene glycol.

7. The method for producing a resin dispersion liquid according to claim 1 or 2, wherein in the step [b], the water-insoluble resin is in a liquid state at a temperature of 69°C or lower.

8. After completion of the step [b], the viscosity of the mixture is 1.0 × 10 ５ The method for producing a resin dispersion according to claim 1 or 2, wherein the viscosity of the resin dispersion is 0.01 to 0.1 mPa·s or less.

9. A method for producing a resin dispersion liquid described in claim 1 or 2, wherein the content ratio (mass ratio) of water to the water-insoluble resin in the mixed liquid after completion of step [b] is 1.5 or less.

10. A method for producing a resin dispersion according to claim 1 or 2, further comprising a step [d] of adding an additive.

11. The method for producing a resin dispersion according to claim 10, wherein the additive added in step [d] is encapsulated in particles of the water-insoluble resin in the resin dispersion.

12. The method for producing a resin dispersion according to claim 10, wherein the additive comprises at least one selected from the group consisting of a polymerization initiator, a sensitizer, and a polymerizable monomer.