JPS6068045A - Production of microcapsule - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing microcapsules with walls formed of l;il' cord/formaldehyde polymers or melamine/formaldehyde polymers. These microcapsules are unique to pressure-sensitive copying materials;
It is not exclusive to the same material.

An example of a conventional pressure-sensitive copying method is U.S. Pat.
0.456@, and is generally called the manifold copying method. The manifold copying system consists of an upper sheet coated with microcapsules containing a colorless color-forming substance solution on the back side, and a lower sheet coated with a color-developing coreactant such as acid clay, phenolic resin, or some organic salts on the front side. It consists of a sheet. When two or more stacked recording materials are required to make multiple copies, multiple intermediate sheets are sandwiched. On the back side of each intermediate sheet are microcapsules containing a colorless coloring substance.
In addition, a color developer co-reactant is coated on each surface.

When writing pressure or printing pressure is applied to these sheets, the microcapsules are destroyed. As a result, the chromogenic material solution is released onto the co-reactant of the next sheet to cause a chemical change and cause the color of the chromogenic material to appear. In the above copying method, the upper sheet is a CB (Coated Back) sheet, and the lower sheet is a CF (Coated Back) sheet.
Front-surface coated) sheets.

On the other hand, the intermediate sheet is CF B (Coated F r
It is well known as an ont and back sheet (coated on both sides).

Another type of pressure sensitive copying system is known as a self-contained system and is disclosed in U.S. Pat. According to the self-contained method, the microcapsules containing the color former solution and the co-reactant are applied on the same side of a single paper sheet. The writing pressure or printing pressure applied to this sheet destroys the capsules and releases the coloring substance, and then the coloring substance reacts with the coreactant on the sheet to develop color.

The microcapsules used in both of the pressure-sensitive copying systems described above must meet a stringent set of physical property requirements. Examples of such physical properties include capsule strength, color, particle size distribution range, and wall adhesion (impermeability). In these pressure-sensitive copying systems, microcapsules prepared by coacervation techniques using natural polymers such as gelatin have been used for many years, but there has been a significant trend in recent years to use microcapsules with walls made of synthetic polymers. The use of microcapsules.

In such a situation, microcapsules whose walls are formed entirely or in part from urea/formaldehyde polymers or melamine/formaldehyde polymers! ! Various Jg methods have been proposed. For example, encapsulation by in-situ reaction of urea and formaldehyde or dimedyllol urea monomers in an aqueous vehicle and in the presence of a negatively charged, carboxyl-substituted, linear aliphatic hydrocarbon-type polyelectrolyte dissolved in the same vehicle. U.S. Pat.
No. 4,087,376 and No. 4.089.80
It is disclosed in No. 2.

The encapsulation method disclosed in U.S. Pat. In the presence of a linear aliphatic hydrocarbon polymer electrolyte, methylolmelamine monomers or low molecular weight polymers thereof, or etherified methylolmelamine monomers or low molecular weight polymers thereof are polycondensed.

Preparation of microcapsules with walls tailored to the polymerization of urea and formaldehyde in the presence of arabicol and, if necessary, an anionic high molecular weight polyelectrolyte such as an acrylic acid copolymer. A method is disclosed in US Patent Specification Box 4.221.710. Illustrated as acrylic acid copolymers are copolymers of acrylic acid and various alkyl acrylates, including ethyl acrylate/acrylic acid copolymers and butyl acrylate/acrylic acid copolymers. According to the disclosure of the patent, the acrylic acid content in the acrylic acid copolymer is preferably about 5-100 mol%.

Ammonium salt of a certain acid and acrylic acid It E
U.S. Patent Specification Box 4 describes a method for producing microcapsules whose walls are adjusted by polymerization of urea and formaldehyde in the presence of an anionic polyelectrolyte. ．． 251
．． No. 386 and No. 4,356.109. Illustrated as acrylic acid copolymers are copolymers of acrylic acid and various alkyl acrylates, including ethyl acrylate/acrylic acid copolymers and butyl acrylate/acrylic acid copolymers. According to the disclosure of both these patent specifications, the preferred content of acrylic acid in the acrylic acid copolymer is about 5-100 mole percent.

U.S. IT, I Patent No. 4,001,140, No. 4゜087.376, No. 4,089,802 and No. 4
．． The encapsulation method of No. 100,103 successfully encapsulates color forming material solutions for pressure sensitive copying paper.

Among the carboxyl-substituted polyelectrolytes disclosed in these patent specifications, a preferred example is a hydrolyzed maleic anhydride copolymer. The most suitable hydrolyzed maleic anhydride copolymer is an ethylene/maleic anhydride copolymer (hereinafter abbreviated as rEMAJ) that is capable of imparting 5 J (hereinafter abbreviated as rEMAJ) with physical properties when encapsulated and polymerized in the completed microcapsule.

Problems to be Solved by the Invention In recent years, the price of EMA has skyrocketed, so microcapsules produced by a method using EMA as a carboxyl-substituted polymer electrolyte inevitably become expensive.

Considering both cost and availability, an alternative to EMA as a carboxyl-substituted polyelectrolyte is polymeric acrylic acid (hereinafter abbreviated as "PAA"). U.S. Patent Specification Boxes 4.001.140 and 4,100.10
As disclosed in No. 3, microcapsules produced by a method using PAA as a carboxyl-substituted polyelectrolyte have commercial quality for pressure-sensitive copying paper, but when using EMA, It does not have the same optimum physical properties as those obtained in the conventional method.

U.S. Patent R'F Specification No. 4.001.140 and No. 4
, 100, 103, the carboxyl-substituted polyelectrolyte has the function of actively controlling or adjusting the polymerization reaction of the starting material used to form the condensation polymer as the constituent material of the finished capsule wall. .

Another function of the polyelectrolyte is to act as an emulsifier, thereby promoting and maintaining the separation of individual droplets of the desired capsule core material in the aqueous vehicle. When PAA is used as a polyelectrolyte, E
Compared to MA, the energy and time required to emulsify the desired capsule core material are high, and the droplet size distribution is degraded. U.S. Patent Specification No. 4,100
In the method of No. 103, the starting material used in the in-situ polymerization reaction (e.g., methylated methylolmelamine monomer or its low molecular weight @polymer) is mixed before emulsification to form a condensation polymer as a material constituting the capsule wall. The low emulsifying ability of PAA can be compensated for by mixing with PAA. If methylated methylolmelamine monomer or its low molecular weight polymer (hereinafter abbreviated as rMMMJ) is present during the emulsification stage of the intended capsule core material, there is a risk of premature polymerization of MMM. To suppress premature reaction of MMM under such conditions, the pl-1 of the PA'A/MMM solution is increased to the highest value at which the desired capsule core material can be emulsified. Once a satisfactory emulsion of the desired capsule core material has been obtained, it is necessary to lower the pH of the emulsion in order to deposit a satisfactory capsule wall within a reasonable time. The method is described in U.S. Patent No. 4. Further improvements have been made by adding certain salts as disclosed in No. 1,44,699. Furthermore, it is possible to use PAA as a polyelectrolyte in combination with certain relative amounts of polyethylene sulfonic acid or its salts.
No. 95.9.

Means for Solving the Problems The object of the present invention is to eliminate the disadvantages of FAA or other defective electrolytes and to make it possible to achieve good manufacturing properties and excellent capsule quality without the need for expensive EMAs. Generally, U.S. Patent No. 4,001,14
No. 0, No. 4.08.7゜376, No. 4.089.80
The object of the present invention is to provide a method for producing microcapsules of the type disclosed in Nos. 2 and 4°100.103.

U.S. Patent Specification No. 4.001, 14C) @, No. 4゜0
87.37'6, No. 4. ．． 089.802 or 4,100,103,
It has been found that when an acrylic acid/alkyl acrylate copolymer is used as a polymer electrolyte, there is a certain critical range for the alkyl acrylate content in the copolymer. This critical range (well, this is the range where the performance and effectiveness are significantly improved compared to the alkyl acrylate content outside the critical range).The critical range of the alkyl acrylate content varies somewhat depending on the type of alkyl acrylate actually used. (Zuru)
. The finding that a critical range of alkyl acrylate content exists is impossible to predict or analogize, and is not taught in any of the prior art cited above. U.S. Pat. However, the acrylic acid content in the copolymer will vary widely (approximately 5-100 mole %) and the corresponding alkyl acrylate content will also vary widely, for example up to about 95 mole %. Moreover, such a wide range of acrylic acid content is disclosed merely as an example in these three patent specifications.

Although it is necessary to set a certain critical range for the alkyl acrylate content in order to improve performance and effectiveness, the above-mentioned prior art does not address this at all.

In evaluating the degree of improvement in performance and effectiveness, at least one of the following criteria was adopted.

1) With respect to acrylic acid/alkyl acrylate, the ability to form an emulsion of the intended capsule core material with a good particle size distribution; 2) with respect to the above emulsion, the stability when adding a starting material for capsule wall formation; 3) with respect to the above emulsion: Stability resistance during encapsulation 4) Impermeability of completed microcapsules As a result of evaluation according to the relevant standards, it was found that the acrylic acid/alkyl acrylate copolymer specified in Table 1 below can contribute to improving performance and effectiveness. found.

Table 1 Alkyl acrylate in copolymer Alkyl group of alkyl acrylate Gold tin (wt%) Ethyl acrylate About 12 to about 30 Propyl acrylate About 6 to about 14 Butyl acrylate About 4 to about 20 amyl acrylate about 2 to about 14 hexyl acrylate about 2 to about 10 cyclohexyl acrylate about 4 to about 12 2-ethylhexyl acrylate about 2 ) preparing a dispersion in which either solid particles or liquid particles of a substantially insoluble capsule core material are dispersed in an aqueous vehicle, the aqueous vehicle comprising (i) melamine/formaldehyde, methylolmelamine monomer; methylol melamine low polymer, methylated methylol melamine monomer, methylated methylol melamine low polymer, urea/formaldehyde, dimethylol urea single solid, dimethylol urea low polymer, methylated dimethylol urea monobase, methylated dimethylol one capsule wall precursor selected from the group consisting of urea oligomers and combinations thereof; (ii) an acrylic acid/alkyl acrylate copolymer;
A method for producing microcapsules comprising the step of in-situ polymerization of the capsule wall precursor to form a polymer shell that individually surrounds particles of the capsule core material, wherein the acrylic acid/alkyl acrylate copolymer is Ethyl acrylate with about 12 to about 30% alkyl acrylate, propyl acrylate with about 6 to about 14% by weight, butyl acrylate with about 4 to about 20%, acrylic with about 2 to about 14% by weight. amyl acid, about 2 to about 1
1 selected from the group consisting of 0 weight percent hexyl acrylate, about 4 to about 12 weight percent cyclohexyl acrylate, and about 2 weight percent 2-ethylhexyl acrylate.
f! l! Provided is a manufacturing method characterized in that:

The most suitable substances among the capsule wall precursors are methylated methylolmelamine, followed by urea and formaldehyde. A good example of other species precursors is U.S. Patent Specification Letter 4,001.
, No. 140, No. 4.087゜376@, No. 4,089,
No. 802 and No. 4°100.10'3, and the operating procedures are generally similar to those disclosed in these patents.
The following can be applied. For suitable examples of capsule core materials, reference should also be made to the above four prior arts.

The amount of acrylic acid/alkyl acrylate copolymer added is preferably from about 0.4 to about 15% by weight of the aqueous vehicle.

Although the 'IjA production process of the present invention is operable under a wide range of temperature conditions, the preferred temperature range is from about 40 to about 95°C. A more preferred temperature range is about 50 to about 70°C.

Suitable examples of the above-mentioned acrylic acid/alkyl acrylate copolymers that can be used in the present invention are copolymers having the following properties.

Appropriate amount in copolymer Optimal amount Alkyl acrylate (wt%) (wt%) Butyl acrylate Approximately 6 = Approximately 10 Approximately 8 Ethyl acrylate Approximately 1
8-about 24 about 22 hexyl acrylate about 2-about 6
about 4 cyclohexyl acrylate about 4 - about 6 about 4 as required
By adding one of the salts described in No. 9, it is possible to improve the viscosity of the resulting microcapsule slurry.

However, salts of this type are unnecessary to achieve the effect intended by the present invention, and U.S. Patent Specification Box 4.221,7
No. 10, No. 4°251.386 and No. 4,356.
Nor are the gum arabic or ammonium salts disclosed in No. 189 used.

The present invention can improve the emulsification of the desired capsule core material, improve the particle size distribution in the emulsion, and increase the stability of the emulsion during encapsulation. The finished capsule exhibits excellent abrasion and stain resistance when applied to copying systems. : Rubbing contamination is contamination caused by relative movement between stacked sheets, for example, during printing or handling of sheets. ).

Example Hereinafter, the present invention will be explained in detail based on Examples described later.

Unless otherwise specified, parts and percentages are by weight and all solutions are aqueous.

The color-forming compound solutions shown in Table 2 were used as the intended capsule core materials in all Examples.

Table 2: fLL Coloring substance 1.7% 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide 0.55% 2--anilino-3--methyl-6'-diethylaminofluorane 0.55% 3,3-bis(1-ethyl-2-methylindol-3-yl)phthalide The solvent for the above color forming compound solution was a mixture of 65 parts of C+aCtq alkylbenzene and 35 parts of benzylated xylene (U.S. Pat. Bookcase 4,130゜299).

The following procedure was used for each of Examples 1-51. water 1
49.5 () and alkyl acrylate/acrylic acid copolymer 3.50 m, the pH was adjusted to 5.0, and the capsule core material 180 (I) from Table 2 was emulsified in 153 (l) of the mixture. A separate second mixture of 6.5 g of the above copolymer and 65.0 (J) of water was prepared and the pH was adjusted to 5.0.
(Resin+ene714), fixed valve 80%, Monsanto Company (MOnSantOCompany)
) ) was then added to the above emulsion with stirring. The resulting mixture was placed in a container placed in a water bath at room temperature and stirred continuously. Water bath at 55℃
encapsulation was started and completed while maintaining the same temperature throughout the day and night.

The above procedure was used for all examples employing polymerization of methylated medylol melamine resin as the capsule wall method. However, when the copolymer was edyl acrylate/acrylic acid, the pH of the second mixture was lowered from 5.0 to 4.0. On the other hand, when the copolymers were acrylic acid, propyl acrylate, amyl acrylate, cyclohexyl acrylate, and 2-ethylhexyl acrylate, the water bath was heated from 55°C to 65°C at the same time as all the components were halved. .

In each example, particle size was measured at each stage after emulsification, after addition of the mixture of regimen and additional copolymer, and after completion of encapsulation. Particle size measurement was performed using a particle size analyzer (Microtrac Particle Size Analyzer (M 1cro).
trac particle 31zeAnalyze
r), Reed & Northrup Instruments (Leeds and Northrup Instruments)
nstruments) and visual measurements using a microscope. The reason for using both methods is that although the above particle size analyzer exhibits extremely high reliability for small particle sizes, it may not be able to detect large particle sizes that can be easily detected with a microscope. .

To track capsule wall formation and detect oversized capsules, we adopted the CF draw-down test, which is similar to the test described in US 1ml Patent Specification No. 4,100,103. did. For Examples 1-51, the encapsulating emulsion containing all of the capsule-forming components was coated onto the reactive CF sheet via a gap coater set at a wet film thickness of 75 microns. Color development occurred due to the reaction between the color forming substance and the co-reactant of the CF sheet. Capsule wall formation was indicated by the fading of the color when the emulsion was applied over time, and the reflectance of the applied area was determined by measuring the opacity. According to this test method, it is possible to detect oversized particles that appear as blue spots visible to the naked eye when the emulsion dries.

Table 3 shows the types of acrylic acid/alkyl acrylate copolymers and the gold teeth of the alkyl acrylates in the copolymers in Examples 1 to 51.

Clothing-a Example Acrylic acid in alkyl Bt copolymer 2 1
2 3 14 4 18 5 22 6 24 7 26 8 30 9 35 10 Propyl 5 11 6 12 8 13 10 14 12 15 14 16 16 17 Butyl 2 18 4 19 6 20 8 21 10 22 12 23 14 24 16 25 20 26 24 27 Amyl 1 28 2 29 4 30 6 31 8 32 10 33 12 34 14 35 18 36 Hexyl 1 37 2 38 4 39 6 40 8 41 10 42 12 43 Cyclohexyl 2 44 4 45 6 46 8 47 12 48 16 492- Ethylhexyl 1 50 2 51 3 Table 4 shows the performance test results of Examples 1 to 51 measured by the above particle size measurement and drawdown test.

From this result, the critical range of alkyl acrylate content for each copolymer can be determined.

Example compositions selected from Examples 1 to 51 were individually mixed with ethoxylated corn starch binder and uncooked wheat starch granules at the following dry mixing ratios.

Sufficient water was added to prepare a 20% solids dispersion.

parts (dry weight) Substance 50 Capsules 5 Ethoxylated corn 5 Starch 12.5 Wheat starch grains 50 (1
111-' base paper and then dried. Each obtained C
Regarding the B receipt, typewriter density (Typ.
cwril:er l ntensity - T T
) and A-bun reduction tests were conducted.

U.S. Patent Specification Box 3,732°120
No. 3,455,721 and having a coating consisting of an oil-soluble metal salt of a phenol/formaldehyde novolak was used. A standard pattern was printed on a CB-CF sheet whose coated surfaces were overlapped with each other. Twenty minutes after the image was developed, its density was measured using a reflectance method. The reflectance of the stamped area is a measure of color development on the CF sheet, and is expressed as the ratio (1/IO>) of the reflectance (1) of the stamped area to the reflectance (10) of the CF receipt substrate.I/ A high Io means poor color development, and a low value ( ] means good color development.

The oven degradation test is a test related to capsule quality that indicates the degree to which a coated sheet loses its ability to form transfer prints in a typewriter test after the capsule coated sheet is stored in an oven at a specified temperature for a specified period of time. Usually,
Regarding the CB-CF sheet set, the CB receipt is stored in an oven at 95° C. for 18 hours, and the CB-CF receipt image is reproduced after storage. Oven storage tests consistently show that bad capsules largely or completely lose their ability to form transfer prints during oven storage, and that good capsules survive oven storage with little or no loss of their ability. There was found.

3 14 Ethyl 53 55 6 24 53 54 11 6 Propyl 53 55 12 8 55 57 13 10 53 55 14 12 54 56 15 14, 54 55 19 6 Butyl 51 56 20 8 46 50 21 10 52 55 22 12 50 54 28 2 Amyl 53 55 29 4 56 58 30 6 57 59 31 8 55 58 32 10 54 56 33 12 60 64 34 14 53 56 37 2 Hexyl 56 59 38 4 ・55 58 39 6 55 56 40 8 55 58 41 10 56 59 44 4 Cyclohexyl 54 5645 6 54
56 46 8 53 57 50 2 2-Ethylhexyl 53 56 As is clear from the test bundles in Table 5, all of the tested CB Seas 1 to 1 maintained good TI image density even after oven storage and exhibited excellent capsule quality. It shows.

Examples 52-57 Encapsulation experiments were conducted similar to Examples 1-51, except that a different capsule wall formation method was used. Example 52
57, the following common procedure was used. Water 89.5
q, 5 g of urea, 0.5 g of resorcinol (+, 5 g of deacrylic acid alkyl acrylic acid copolymer) were mixed, and the pH was adjusted to 4.0.

Into this mixture, 90σ of the desired capsule core material shown in Table 2 was emulsified. The resulting emulsion was placed in a container placed in a water bath at room temperature and, after continuous stirring, 13.5 (+) of 37% formaldehyde solution was added. The water bath was heated to 55 °C and at the same temperature 1 Encapsulation was completed by maintaining it day and night.

Each of the capsules thus formed passed the particle size measurement test. According to the method described above, this capsule was applied to a C'B sheet, and a coated CB receipt TI test and an oven degradation test were conducted. The results are shown in Table 6.

Alkyl acrylate in copolymer typewriter temperature example Content Alkyl group Oven Oven (% by weight) Before storage After storage 5218 Ethyl 5656 53 8 Propyl 5959 54 6 Amyl 5757 55 8 Hexyl 5454 56 4 Cyclohexyl 5656 5722 -Ethylhexyl 5556 Various alkyl acrylate/acrylic acid copolymers exhibit excellent effects when applied to methods for manufacturing microcapsules in which the polymer shell of the microcapsules is formed by in-situ polymerization of urea and formaldehyde. This is clear from the results of the TI test and oven storage test.

patent applicant Appleton Papers Incorporated

Claims (1)

[Scope of Claims] [1] (a) A step of preparing a dispersion in which either solid particles or liquid particles of a substantially insoluble capsule core material are dispersed in an aqueous vehicle, wherein the aqueous vehicle is (i>Melamine/formaldehyde, methylol melamine monohung, methylol melamine low polymer, methylated methylol melamine monomer, methylated methylol melamine low polymer, urea/formaldehyde, dimethylol urea monomer, dimethylol urea low polymer , methylated dimethylol urea monomer, methylated dimethylol urea oligomer, and combinations thereof; and (ii) an acrylic acid/alkyl acrylate copolymer. and (b) forming a polymer shell that individually surrounds particles of the capsule core material by in-situ polymerization of the capsule wall precursor, wherein the acrylic acid/acrylic acid The alkyl acrylate of the alkyl copolymer is about 12 to about 30% by weight of ethyl acrylate, about 6 to about 14% by weight of propyl acrylate, about 4% by weight of alkyl acrylate;
from about 20% to about 20% butyl acrylate, from about 2% to about 14% amyl acrylate, from about 2% to about 10% by weight
% hexyl acrylate, from about 4 to about 12% by weight
A method for producing microcapsules, characterized in that the microcapsules are one selected from the group consisting of about 2% by weight of cyclohexyl acrylate and about 2% by weight of 2-ethylhexyl acrylate. [2] The manufacturing method according to claim 1, wherein the amount of the acrylic M/alkyl acrylate copolymer added is about 4 to about 15% based on the weight of the aqueous vehicle. [3] Claim 1, wherein the in-situ polymerization is carried out at a temperature of about 40 to about 95°C.
The manufacturing method according to item 1 or 2. [4] The manufacturing method according to claim 3, wherein the in-situ polymerization is carried out at a temperature of about 50 to about 70°C. (5) Claim 1, wherein the alkyl acrylate of the acrylic acid/alkyl acrylate copolymer is about 6 to about 10% by weight of butyl acrylate.
The manufacturing method according to any one of Items 4 to 4. [6] The production method according to claim 5, wherein the alkyl acrylate of the acrylic acid/alkyl acrylate copolymer is about 8% by weight of ethyl acrylate. [7] Any one of claims 1 to 4, wherein the alkyl acrylate of the Acrylic M/alkyl acrylate copolymer is about 18 to about 24% by weight of ethyl acrylate. The manufacturing method according to item 1. [8] The manufacturing method according to claim 7, wherein the alkyl acrylate of the acrylic acid/alkyl acrylate copolymer is about 22% by weight of ethyl acrylate. [9] Claim 1, wherein the alkyl acrylate of the acrylic acid/alkyl acrylate copolymer is about 2 to about 6% by weight of hexyl acrylate.
The manufacturing method according to any one of Items 4 to 4. [10] The production method according to claim 9, wherein the alkyl acrylate of the acrylic acid/alkyl acrylate copolymer is about 4% by weight of hexyl acrylate. (11) Any one of claims 1 to 4, wherein the alkyl acrylate of the acrylic acid/alkyl acrylate copolymer is about 4 to about 6% by weight of cyclohexyl acrylate. The manufacturing method according to claim 1. [12] Claim 11, wherein the alkyl acrylate of the acrylic acid/alkyl acrylate copolymer is about 4% by weight of cyclohexyl acrylate.
Manufacturing method described in section.