JPH0499691A - Microcapsule for pressure-sensitive recording sheet and preparation thereof - Google Patents

Abstract

PURPOSE:To obtain a microcapsule, which has a melamine/formaldehyde resin wall, having sharp particle size distribution by passing a solution of an electron donating color former in a hydrophobic liquid through the gap between a rotor and a stator to continuously perform emulsification and specifying the viscosity of the hydrophobic liquid dissolving the electron donating color former. CONSTITUTION:A solution of an electron donating color former in a hydrophobic liquid is emulsified in an aqueous solution of a hydrophilic high-molecular compound and the hydrophobic liquid droplet is encapsulated by a melamine/formaldehyde resin wall. At this time, emulsification is continuously performed by an emulsifying machine using the gap between a rotor and a stator and viscosity of the hydrophobia liquid dissolving the electron donating color former is set to 6-20cp at 25 deg.C. The obtained melamine/formaldehyde microcapsule has sharp particle size distribution and the particle size and particle size distribution thereof are within a range of 4.0mum<=D50<=12.0mum and a range of D90/D10<=2.0. In the formulae D10, D50 and D90 are a percent particle size calculated from cumulated volume distribution, D10 is a cumulated 10% particle size, D50 is a cumulated 50% particle size and D90 is a cumulated 90% particle size.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to microcapsules for pressure-sensitive recording sheets that utilize a color-forming reaction between a colorless electron-donating dye and an electron-accepting compound, and a method for producing the same. % is characterized by the process of forming an oil-in-water emulsion, producing microcapsules with uniform particle size &! The present invention concerns a manufacturing method and microcapsules with uniform particle size.

(Prior art) A pressure-sensitive recording sheet supports a microcapsule layer containing microcapsules in which a colorless electron-donating dye (hereinafter referred to as a coloring agent) is dissolved in an appropriate solvent and the resulting oil droplets are microencapsulated. An upper paper coated on one support, a lower paper coated with a color developer containing an electron-accepting compound (hereinafter referred to as a color developer) on the other support, and in some cases, one paper coated on one of the supports. A support consisting of a combination of medium paper coated with a microcapsule layer on one side and a color developer layer on the other side, or a support containing the capsules and a color developer on the same side;
Alternatively, the support may contain one of the capsules or the color developer and be coated with the other.

These pressure-sensitive recording sheets are described, for example, in U.S. Patent No. λ, 30
6. ≠No. 70, same, 2. zos, AT number, same! !
rO, 4t7/issue, λ, 730.457, j, I
I/r, 2! It is described in No. θ, etc.

Methods for producing microcapsules for pressure-sensitive recording sheets include coacervation method, interface 1 method, and 1n-situ method.
Polymerization methods are known. Regarding the coacervation method, see U.S. Patent WJ Co., 100. tl, g7 issue, same J,
Too, art issue, same J, l, 17゜ttj shout,
For interfacial polymerization methods, see U.S. Pat.
No. 7, same 3. j77, jt/! No. 3. rrt, or
In the T volume, the 1n-situ polymerization method is US%! P
! FW! ,! , 7. ! A, toy number, same 3.
It is described in 7ri7.4jri issue etc.

Among these, melamine formaldehyde resin microcapsules are widely used in pressure-sensitive recording paper as a representative type of 1n-situ polymerized microcapsules.

Microcapsules using melamine-formaldehyde resin have features such as being able to obtain a highly concentrated capsule liquid and having superior aqueous properties compared to microcapsules made using gelatin coacervation, which has been widely used in the past. There is.

However, conventionally known microcapsules using melamine formaldehyde resin do not necessarily have satisfactory performance.

This is because conventional microcapsules have a relatively wide particle size distribution, and capsules that are much smaller than the average particle size are not destroyed during color development and do not contribute to color development, and capsules that are too large are easily destroyed by low pressure, causing pressure warping. Therefore, in manufacturing good pressure-sensitive copying paper, it is an important technique to obtain capsules with a desired particle size and a narrow particle size distribution.

(Object of the Invention) An object of the present invention is to provide a microcapsule for a pressure-sensitive recording sheet having a melamine formaldehyde resin wall and having an extremely sharp particle size distribution.

(Structure of the Invention) The object of the present invention is to emulsify a solution of an electron-donating coloring agent dissolved in a hydrophobic liquid in an aqueous solution of a hydrophilic polymer compound, and then
In the manufacturing method of microcapsules for pressure-sensitive recording sheets, in which hydrophobic droplets are encapsulated with a melamine-formaldehyde resin wall, emulsification is performed continuously in an emulsifying machine that utilizes the gap between a rotor and a stator, and an electron-donating color former is When the viscosity of the hydrophobic liquid to be dissolved is 2z Dc, A cp~
Coupled by # manufacturing method with 3θCp.

The above viscosity represents the value measured by the FiB type viscometer, but the viscosity is t
If it is thicker than cp, J., or 30 cp, it will not be possible to obtain microcapsules with a sufficiently sharp particle size distribution.

A more preferred range of viscosity is Icp-20 (p).

The melamine formaldehyde microcapsules obtained by the above production method are characterized in that they have an extremely sharp particle size distribution, and the particle size and particle size distribution are within the following ranges.

II, Op≦l1so≦ia, oμ D9o / Dzo≦ko, O 1) so above represents the median diameter, but I) so is 4
If t and Qμ are small, sufficient color development cannot be obtained, and /
If it is larger than Oμ, sufficient pressure resistance cannot be obtained. I)
The preferred range of so is Fi3.0 to io.

μ, and I) a more preferable range of so is i; [, j to t
.

! μ.

Deo/D1o represents how sharp the particle size distribution is, and the smaller the value of D90/DIO is /JS, the sharper the particle size distribution is. As for microcapsules for pressure-sensitive recording sheets, it is expected that the sharper the particle size distribution, the better the color development and pressure resistance.

The reason for this is that capsules much smaller than the median diameter are not destroyed during color development and do not contribute to color development, and capsules that are too thick are likely to be destroyed by low pressure and cause pressure fog.

The emulsion formation process is considered to be an important process for controlling the particle size distribution of microcapsules. This is because if an emulsion with a uniform particle size is formed in the emulsification process and encapsulation is performed at the interface, microcapsules that reflect the particle size and particle size distribution of the emulsion can be obtained.

Commonly used emulsifiers include simple stirrers, homogenizers, homomixers, and desolpas.
These emulsifying machines have the following disadvantages. (1) The emulsifying area is limited to the very periphery of the emulsifying blade. (2) Shearing force becomes non-uniform near and far from the center of rotation of the emulsifying blade. It is thought that these causes widen the particle size distribution.

The present invention provides a method for producing microcapsules using an emulsifier that applies strong shearing force in a narrow gap between a rotor and a stator, unlike an emulsion process using a conventional emulsifier that utilizes the rotation of emulsifying blades. That is, a hydrophobic liquid and a hydrophilic liquid are mixed, and the mixed liquid is sent to the gap between the rotor and the stator to form an oil-in-water emulsion. In other words, an emulsifying region where a stable shearing force can be obtained is formed in the narrow gap between the rotor and stator, and by passing the remaining liquid through this emulsifying region, an oil-in-water emulsion is formed, and then a wall film forming process is performed. The purpose of this method is to obtain microcapsules with a narrow particle size distribution.

Examples of emulsifiers using a rotor and stator include colloid mills and double cylindrical emulsifiers with uniform gaps.

In addition, the present invention provides that the viscosity of the hydrophobic liquid affects the particle size distribution in the emulsification step, and that the viscosity of the hydrophobic liquid has a t c
It has the characteristic that the particle size distribution becomes sharp at p~J Ocp. This is because if the viscosity of the hydrophobic liquid is larger than JOcp, it becomes difficult for oil droplets to break up, leaving particles larger than the average diameter, whereas if it is smaller than Acp, the viscous resistance of the oil droplets is small, causing irregular breakup. Particles smaller than the average particle size remain. The viscosity (A
cp ~ 30 cp), the probability that an oil droplet will split into two oil droplets of approximately the same size increases, and it is thought that the particle size distribution becomes sharper.

The present inventors confirmed what effect the viscosity of a hydrophobic liquid has on the particle size distribution using an emulsification method that utilizes the gap between a rotor and a stator. That is, hydrophobic liquids of various viscosities containing a coloring agent in a hydrophilic liquid are emulsified using an emulsifying machine that utilizes the gap between a rotor and a stator, and after a wall film formation process is performed with melamine formaldehyde resin, the resulting microcapsule particles are The diameter distribution was evaluated. Furthermore, in order to confirm the effect of sharpening the particle size distribution, the particle size distribution was
/DIO=/, 7 to a, o Capsules were prepared in a wide range of values, and their color development and pressure resistance were evaluated.

The emulsifier used was a colloid mill that applied strong shear in the gap between the rotor and stator, and the resulting particle size distribution strongly depended on the viscosity of the hydrophobic liquid, with a viscosity of i: A cp ~ J
D90/DIO≦2. The particle size distribution became sharp.

As a result of evaluating the color development and side pressure properties of microcapsules with various particle size distributions by changing the viscosity of the hydrophobic liquid, D90
There is a clear difference between microcapsules in the range of D90/DIO'', 1Lt-j, 0 and microcapsules in the range of D90/DIO≦-4O, and D90/DIO≦2.
．． Microcapsules in the range of O have D90/
The color development and pressure resistance were superior to microcapsules in the range of DIO=co, 4t-a, and o.

The melamine formaldehyde resin-walled microcapsules of the present invention are produced by emulsifying and dispersing a solution of a color former in a hydrophobic liquid in a hydrophilic liquid, and then mixing an aqueous solution of a melamine formaldehyde initial condensate with the emulsion. Obtained by coating with resin.

Coloring agents used in the present invention include triphenylmethane phthalide compounds, fluoran compounds, phenothiazine compounds, indolyl phthalide compounds, indolyl azaphthalide compounds, leucoauramine compounds,
Examples include rhodamine lactam compounds, triphenylmethane compounds, triazene compounds, and spiropyran compounds.

As the hydrophobic liquid, natural or synthetic oils can be used alone or in combination. Examples of hydrophobic liquids include kerosene, paraffin, naphthenic oil, alkylated biphenyls, IS-containing normal-ξ-laffin, alkylated naphthalenes, diarylalkane, and dibasic acid esters such as phthalate esters. The viscosity at 0C is t cp~30
Select and use cp.

A specific example is diethyl diphenyl (10 cp
), diimpropylna 2-talene (t cp ), /-phenyl-/-xylylethane (7 cp ), degree of chlorination 3
0wt Cl2-chlorinated normal e-roughin (t
cp), etc.

Furthermore, as the hydrophilic liquid, there is used one that has a function as an acid catalyst that promotes the polycondensation reaction of melamine formaldehyde resin in addition to the usual function of a colloid for health care.

Specific examples include Fi, styrene sulfonic acid polymers, copolymers of styrene and maleic anhydride, copolymers of ethylene and maleic anhydride, gum arabic, polyacrylics, copolymers of acrylic acid and acrylic esters, etc. can be sheep.

The microcapsules obtained in the present invention are added with a general water-soluble binder, a latex binder, and a capsule anti-slip agent such as cellulose powder, starch particles, talc, etc. to obtain a microcapsule drumstick liquid for pressure-sensitive recording sheets.

Examples of the color developer that reacts with the color former used in the recording sheet of the present invention include clay materials such as dispersible clay, activated silica, attapulgite, zeolite, indonite, and kaolin, and metals such as aromatic carbonate. Examples include salts and phenolic resins.

These color developers are applied to a support such as paper along with a binder such as styrene butadiene latex.

The performance of the microcapsule sheet for pressure-sensitive recording of the present invention was tested using the following color developer sheet.

[Adjustment of color developer sheet]

[Preparation of dispersion liquid] 3. Using 75 parts of zinc j-di-α-methylbenzylsalicylate, 20 parts of calcium carbonate, 30 parts of activated clay, 20 parts of zinc oxide, 1 part of sodium hensametaphosphate and 00 parts of water, A dispersion liquid (A) was obtained by uniformly dispersing the particles using a sand grinder so that the average particle size was 3 μm.

[p of coating liquid! Adjustment]

11.00 parts of dispersion liquid (A), 10 parts of a 70-chi PVA-203 (manufactured by Kuraray) aqueous solution, 100 parts of a 10-chi PVA-//7 (manufactured by Kuraray) aqueous solution, and carboquine-modified SBR latex (SN-3o7 manufactured by Sumitomo Nogatatsufu) 10 parts (in terms of solid content) were added, and water was added to adjust the solid content concentration to -O to obtain a coating liquid.

[Application of color developer sheet]

This coating liquid! 6.0g7m on Og/m2 base paper
The color developer sheet was coated using an air knife coater so that the solid content of No. 2 was coated and dried to obtain a color developer sheet.

The following examples will specifically clarify the invention, but it is important to note that the invention is limited to examples of the present invention.

(Example) In the following examples, the average particle size and particle size distribution were measured using a Coulter Counter TA ■ type particle measuring device (manufactured by Coulter Electronics, Inc., USA). H represents the weight, and viscosity represents the value of -j0C.

Example 1 Chlorinated normal flax fin (
The average carbon number/-1 chlorination degree is 30wt and the viscosity is Icp,
The average number of carbon atoms/k, the degree of chlorination eOwt, and the viscosity/3
cp, average carbon number 72, chlorination degree OW 1% and average carbon number / ko, chlorination degree 30wt 7 pairs/blend, viscosity is Acp, average carbon number / -1 chlorination degree 4tOwt and average carbon number 7.2, Dissolve 100 g of crystal violet lactone as a coloring agent in 2000 g of chlorination degree jOwt% / blend with a viscosity of 7
The following solution was prepared. There was almost no change in the viscosity of the chlorinated normal paraffin using a B-type viscometer due to the addition of the coloring agent.

Next, a partial sodium salt of polyvinylbenzenesulfonic acid (manufactured by National Starch, VER8A) was used.

A secondary solution was prepared by dissolving TLroo)aoog in hot water +2 r 00 gK and then cooling.

The secondary solution was stirred using a propeller blade agitator with a blade diameter of 70 mm.
While stirring at pm, the seventh solution was poured to form an oil-in-water emulsion, and a preliminary emulsion was obtained.

Next, apply this pre-emulsified liquid to a colloid mill (manufactured by Nippon Seiki Seisakusho, product name: "On-vehicle colloid mill").Flow rate = 0.Ak
g/min, clearance = 6ooμ, rotation speed = / s 0
An emulsion with a particle size of 7 μm was obtained by processing under the conditions of 0~/J' 00 rpm and number of passes = 1 time. Separately, melamine/μOg, 37% by weight formaldehyde aqueous solution JO
After 30 minutes, a transparent aqueous solution of melamine, formaldehyde and melamine-formaldehyde initial condensate was obtained. This aqueous solution was mixed with the above emulsion. While stirring, adjust the pH to t, oKw4 with a 2M phosphoric acid solution, and raise the liquid temperature to 7J 0CK2.
Stirring was continued for an hour. The capsule liquid was cooled to room temperature and adjusted to pH 9.01 fJ with an aqueous sodium hydroxide solution.

When the particle size distribution of this capsule was measured with a Coulter Counter TAII model when the particle size was 7μ, it was found that when the viscosity of the chlorinated normal millirough fin was 1″cp, D90/D
When 10=/ , 7o, / j cp, D90/DI (
1=/, 7t%A cp when DIO/DIO=/
, 77.2 I cp when I)90 /D10 =/
, 74.

To the thus obtained capsule liquid, 2000 g of /j% aqueous solution of polyvinyl alcohol and carboxy-modified SBR were added.
Aooog latex in solid content.

7200 g of starch particles (average particle size l!μ) were added.

Next, water was added to adjust the solid content concentration to 0.05 to 100% to prepare a coating solution.

This coating solution was dried on a dry cloth using an air knife casing machine at a dry weight of 4 tOg/m2 to obtain a microcapsule sheet.

In Example/Example/, the conditions for processing the pre-emulsified liquid with a colloid mill are as follows: flow rate i = 0, 4tkg 7 minutes, clearance -400μ, rotation speed = izoo~/1oorp.
A microcapsule sheet was obtained in the same manner as in Example 1 except that the conditions were changed to m, number of passes = / times.

When the particle size distribution of this capsule was measured using a Coulter Counter TAn model, it was found that the viscosity of the chlorinated normal paraffin was 1 cp, and the particle size distribution was DIO/DIO= / , 77, / J When cp, I) 90 /DIQ = / , 7 u, l When cp, D90/DIO: / , 71,21 When cp, D
90/L'lO=7,7 J.

Comparative Example/A microcapsule sheet was obtained in the same manner as in Example/, except that the viscosity of the chlorinated normal paraffin in Example/ was changed to the following viscosity (average number of carbon fibers/co, degree of chlorination,
Viscosity is 4t cp at 20wt, average carbon number/-1 degree of chlorination! The viscosity is 73 cp at Owt%, the number of Hiramoto carbon atoms/l, the chlorination degree is GJwt%, and the viscosity is /Ocp).

When the particle size distribution of this capsule was measured with a Coulter Counter TAfi type when the particle size was 7μ, it was found that chlorinated normal? When the viscosity of the rough-in is μcp, the particle size distribution 11 DIO/Dlo = J, t, 73
D90 when cp /DIO: J, J, /f O
When Cp, D90/DIO = 3, 3 T hfc.

Comparative Example The procedure was the same as in Example 2, except that the viscosity of the chlorinated Tsurumaruba/1F 7 was changed to 4t cp, 73 cp1/lOCp (!I! is the same as Comparative Example 1). I got microcapsule sheetra.

When the particle size distribution of Konocapsules was measured using a Coulter Counter TAL [type] and the particle size was 7μ, it was found that the viscosity of chlorinated normal nano (rough-in CP) was D90/
DIO == 3. D90/D when J', 7jcp
When IQ = J, J, lriOcp, D90/D10
= 3, II.

Example 3 Diimpropyl naphtha V72000g and polyisobutyl methacrylate (manufactured by Genon Kasei Co., Ltd., trade name "Acrybase rooiJ", 30g%jjg, 71g, 10g
Dissolve and adjust the viscosity of the oily liquid to tcp%10cp,/lcp,
+20cp,! 0 cpK was prepared. Crystal-2 iolet lactone/θOg was dissolved in each of these oily liquids to prepare five primary solutions. The viscosity of the oil-based liquid changes little when measured with a B-type viscometer due to addition before color development.

While stirring the secondary solution of Example 1 at roorpm using a propeller blade stirrer with a blade diameter of 70 mm, the above three primary solutions were poured to form a type of oil-in-water emulsion and a preliminary emulsion.

Next this! Two preliminary emulsions were emulsified using a colloid mill under the same conditions as in Example 1 to obtain a capsule sheet.

When the particle size distribution of this capsule was measured using a Coulter Counter TAL type when the particle size was 7 μ, it was found that when the viscosity of the oily liquid was t cp, D9 (1/D1o = /, 74, /
When Ocp, D9Q/DIQ=/, 70°/!
For cp, D90/D10=/, 7J, for 20 cp, D9o/D20=i, 7a, and for 30 cp, D90/D16=/, 7i.

Comparative Example 3 Diimprovir Natsutafu 2000g IC polyisobutyl methacrylate/4tOg, and! Add OOg,
The viscosity of oil-based liquids! Ocp, 70cpKv@ was manufactured. Furthermore, 3g of polyimbutylmethacrine-g and 3g of diisopropylnaphthalene and C-/coin paraffin were added to 24toog of the mixed solution to adjust the viscosity of the oily liquid to e cp,
! cpt/Cp4 was adjusted. Crystal violet lactone in each of these one oily liquid! 00g was dissolved to prepare μ 7th solution. The viscosity of the oily liquid hardly changed as measured by a B-type viscometer due to the addition of the coloring agent.

The mixture was pressed and emulsified in a colloid mill in the same manner as in Example 3 to obtain a capsule sheet.

Average particle size by Coulter Counter TAi type 7.0μ
The particle size distribution is shown below. When the viscosity of the oil-based liquid is jOcp, Dg□/DIO=3, when 2.70 cp, Deo/D10=3.3, II (when p, D90
/D16=3. When t, jCp, D90/DIO=
It was J, i.

Comparative Example 1 Diisopropylnaphthalene 2ooog (t by B-type viscometer)
100g of crystal violet lactone in cp)
The primary solution was prepared by dissolving. The viscosity tLid of the oily liquid hardly changed due to the addition of the coloring agent.

Using a propeller blade stirrer with a blade diameter of 70 mm, the secondary solution of Example 1 was mixed with rDOrpm''t' [while stirring, the seventh solution was poured to form an oil-in-water emulsion, and a preliminary emulsion was obtained.

Next, this preliminary emulsion was continuously stirred for 1 minute using a Daysilver blade with a diameter of 100 mm to obtain an emulsion with a particle size of 7 μm.

The rest was encapsulated in the same manner as in Example 1 to obtain a capsule sheet.

When the particle size distribution of this capsule was measured with a 7ter TAII type when the particle size was 7μ, it was D
90/DIG=a, 3.

An evaluation test was conducted on the combination of each of the above microcapsule sheets and the color developer sheet as a pressure-sensitive recording sheet, and the results are listed in Table 1. The evaluation test was conducted using the following method.

/] Color development test Layer each microcapsule sheet with a color developer sheet.IBM
j7μ7 type electronic typewriter (Alphabella) /J
- The letter m was printed with continuous pressure to develop color. After coloring 1
After one day had passed, the print density D (type-wrjter) in the visible region was measured using a Macbeth RD-ta/l type densitometer.

e) Pressure resistance test Lay each microcapsule sheet on a color developer sheet for 10k
A load of g/cm2 was applied to produce pressure fog on the surface of the color developer sheet. After aging these samples for 3 days,
The concentration D (fog) of Capri on the surface of the developer sheet of Deb/Onm was measured using a Hitachi Color Analyzer Model 307.

The microcapsules obtained by the production method of the present invention have an extremely sharp particle size distribution, and the microcapsule sheets using microcapsules with this extremely sharp particle size distribution are different from the microcapsules for comparison as shown in Table 1. It has excellent color development and pressure resistance compared to capsule sheets, and has extremely good performance.

Claims (2)

[Claims] (1) For pressure-sensitive recording sheets in which a solution of an electron-donating coloring agent dissolved in a hydrophobic liquid is emulsified in an aqueous solution of a hydrophilic polymer compound, and then droplets of the hydrophobic liquid are encapsulated with a melamine formaldehyde resin wall. In the method for manufacturing microcapsules, a solution of an electron-donating color former dissolved in a hydrophobic liquid is continuously emulsified by passing through a gap between a rotor and a stator, and the hydrophobic liquid dissolves the electron-donating color former. The viscosity of is 6cp~30cp at 25℃
A method for producing microcapsules for pressure-sensitive recording sheets, characterized in that: (2) In a microcapsule for a pressure-sensitive recording sheet, which contains a solution of an electron-donating coloring agent dissolved in a hydrophobic liquid as a core material, the microcapsule wall is a melamine formaldehyde resin wall, and the microcapsule particles Microcapsules for pressure-sensitive recording sheets characterized by having a diameter distribution within the following range. 4, 0μ≦D_5_0≦12.0μ D_9_0/D_1_0≦2.0 [In the above formula, D_1_0, D_5_0 and D_9_0 are percent particle diameters determined from cumulative volume distribution. D_1_0 - Cumulative 10% particle diameter D_5_0 - Cumulative 50% particle diameter D_9_0 - Cumulative 90% particle diameter]