JPH04265786A - Microcapsule for pressure-sensitive recording sheet - Google Patents

Abstract

PURPOSE:To provide the above microcapsule excellent in solvent resistance and heat resistance. CONSTITUTION:The wall of a microcapsule is formed from aromatic polyvalent rsocyanate composed of carbodrmrde modified diphenylmethane diisocyanate and/or polymethylene polyphenyl isocyanate, aliphatic polyvalent isocyanate and an epoxy compound.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to microcapsules for pressure-sensitive recording sheets that utilize a color-forming reaction between an electron-donating color former and an electron-accepting compound.

0002

[Prior Art] Pressure-sensitive recording sheets are produced by dissolving a nearly colorless electron-donating dye (hereinafter referred to as a coloring agent) in a suitable solvent.
A top paper coated with a microcapsule layer containing microcapsules containing the oil droplets on a support;
A base paper with a color developing layer containing an electron-accepting compound (hereinafter referred to as a color developer) coated on another support, and in some cases, a microcapsule layer on one side of the support and a microcapsule layer on the other side. consisting of a combination of medium paper coated with a color developer layer,
Alternatively, there is a support in which the capsules and the color developer are contained on the same side of the support, or a support in which either the capsules or the color developer is contained and the other is coated. These pressure-sensitive recording sheets are disclosed in, for example, U.S. Patent No.
No. 2,505,470, No. 2,505,489, No. 2,550,471, No. 2,730,457,
No. 3,418,250, etc.

[0003] Methods for producing microcapsules for pressure-sensitive recording sheets include coacervation method, interfacial polymerization method, i
N-situ polymerization methods and the like are known. For the coacervation method, see U.S. Patent No. 2,800,457;
No. 2,800,458, No. 3,687,865, etc., and U.S. Patent No. 3,429,8 regarding the interfacial polymerization method.
No. 27, No. 3,577,515, No. 3,886,
No. 085, etc., and U.S. Patent Nos. 3,726,804 and 3,796,669 regarding the in-situ polymerization method.
It is stated in the number etc. Among these, interfacial polymerization method using polyurethane urea film made by reacting polyvalent isocyanate with water, polyvalent amines or polyhydric alcohols, i
Microcapsules produced by n-situ polymerization have attracted attention in recent years. Microcapsules using a polyurethane urea membrane can yield a highly concentrated capsule liquid and have superior water resistance compared to microcapsules made using coacervation method using gelatin, which has been widely used in the past.
It has the advantage of being able to perform encapsulation in a short time. However, conventionally known microcapsules using polyurethaneurea membranes have the following drawbacks. 1) Solvent resistance is insufficient. The core substance within the capsule is extracted by contact with an organic solvent or by being placed in an organic solvent atmosphere. 2) Heat resistance is insufficient. If the capsule sheet is stored at high temperatures, the core material inside the capsule will leak out of the capsule.

[0004] Also, as a wall material for microcapsules,
The use of aromatic polyvalent isocyanates and aliphatic isocyanates, and the use of aromatic polyvalent isocyanates, aliphatic isocyanates and polyvalent amines is disclosed in JP-A-63-33474.
No. 58-3898, however, there are some problems with solvent resistance, heat resistance, etc.

Furthermore, in microcapsules for pressure-sensitive recording sheets containing a solution of an electron-donating coloring agent dissolved in a hydrophobic liquid as a core material, the walls of the microcapsules are made of aromatic polyvalent isocyanate. One using carbodiimide-modified diphenylmethane diisocyanate (JP-A-2-34386) and one using polymethylene polyphenylisocyanate (
JP-A-56-11374) has been proposed. These microcapsules have a three-dimensional mesh-like dense and strong wall film with a high degree of polymerization, and therefore have excellent pressure resistance.

[0006]

[Problem to be solved by the invention] However, in recent years, NIP (Non
Pressure-sensitive paper for impact printers has been expanding, and microcapsules used for NIP are required to have stronger heat resistance. In the present invention, as a result of further intensive studies on the above two encapsulation methods, the present invention was achieved by discovering that heat resistance can be improved by adding an epoxy compound to the wall material of microcapsules. Therefore, an object of the present invention is to provide microcapsules for pressure-sensitive recording sheets using a polyurethane urea film having excellent solvent resistance and heat resistance.

[0007]

[Means for Solving the Problems] An object of the present invention is to provide microcapsules for pressure-sensitive recording sheets containing a solution of an electron-donating coloring agent dissolved in a hydrophobic liquid as a core material in the microcapsules. The wall is formed of an aromatic polyvalent isocyanate, an aliphatic polyvalent isocyanate, and an epoxy compound, and is characterized in that carbodiimide-modified diphenylmethane diisocyanate and/or polymethylene polyphenylisocyanate is used as the aromatic polyvalent isocyanate. This was achieved using microcapsules for pressure-sensitive recording sheets.

The present invention will be explained in detail below. As described above, the walls of the microcapsules of the present invention are formed from an aromatic polyisocyanate, an aliphatic polyisocyanate, and an epoxy compound, and by adding the epoxy compound, the heat resistance is significantly improved.

The epoxy compound used in the present invention refers to a compound containing a three-membered epoxy group formed from two carbon atoms and one oxygen atom. The reason why heat resistance is improved by adding an epoxy compound is that the epoxy group in the epoxy compound reacts with the urethane bond to form a three-dimensional network-like dense capsule wall. Therefore, the epoxy compound used in the present invention is not particularly limited as long as it is oil-soluble and has one or more epoxy groups. Specific examples of epoxy compounds include epichlorohydrin, cyclohexene oxide, 1,2 epoxyethylbenzene, propylene oxide,
Examples include phenylglycidyl ether, bisphenol A-based epoxy compounds, novolak-based epoxy compounds, and polyphenol-based epoxy compounds.

The carbodiimide-modified diphenylmethane diisocyanate used in the present invention is prepared by adding a phosphorus compound,
For example, it can be obtained by adding phospholine, phosphoridine, phospholine oxide, phospholine sulfide, or metal carbonyl. The main component is −
A linear polycarbodiimide with N=C=N-bonds is obtained, but a uretonimine, which is a cycloadduct of NCO, is partially produced.

Specific examples of the polymethylene polyphenylisocyanate used in the present invention include triphenyldimethylene triisocyanate, tetraphenyltrimethylenetetraisocyanate, and pentaphenyltetramethylenepentaisocyanate. Each of the above components may be used alone or in combination of two or more.

Specific examples of the aliphatic polyisocyanate used in the present invention include hexamethylene diisocyanate, propylene-1,2-diisocyanate, butylene-1,2-diisocyanate, ethyridine diisocyanate, and cyclohexylene-1,4-diisocyanate. - diisocyanate, isophorone diisocyanate, an adduct of hexamethylene diisocyanate and trimethylolpropane, a biuret form of hexamethylene diisocyanate, an isocyanurate form of hexamethylene diisocyanate, an isocyanurate form of isophorone diisocyanurate, etc. In addition to polyvalent isocyanates and epoxy compounds, polyvalent hydroxy compounds and polyvalent amines can also be used as wall materials for microcapsules.

Examples of polyvalent hydroxy compounds include aliphatic or aromatic polyhydric alcohols, hydroxy polyesters, hydroxy polyalkylene ethers, and alkylene oxide adducts of polyvalent amines. Among these, alkylene oxide adducts of amines, such as butylene oxide adducts of ethylenediamine, are preferred.

[0014] Polyvalent amine refers to two or more -N
Refers to compounds with H- or -NH2 groups that are soluble in hydrophilic liquids. Examples of polyvalent amines include aliphatic polyvalent amines, aromatic polyvalent amines, alicyclic polyvalent amines, heterocyclic polyvalent amines, and the like.

Color formers used in the present invention include triphenylmethane phthalide compounds, fluoran compounds, phenothiazine compounds, indolyl phthalide compounds, indolyl azaphthalide compounds, leuco auramine 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 solvents include kerosene, paraffin, naphthenic oil, alkylated biphenyls,
Examples include alkylated terphenyls, chlorinated paraffins, alkylated naphthalenes, diarylalkane, and phthalate esters. Further, as the hydrophilic liquid, an aqueous solution of a protective colloid and/or a surfactant is used. Examples of protective colloids include hydrophilic polymeric substances such as gelatin, gum arabic, casein, sodium carboxymethyl cellulose, starch, and polyvinyl alcohol. Examples of surfactants include ionic ones such as alkylbenzene sulfonic acids, polyoxyethylene sulfates, and funnel oil, and nonionic ones such as polyoxyethylene alkyl ethers, polyoxyethylene, and sorbitan fatty acid esters. be. The volume average particle size of the microcapsules is preferably from 2 to 10 microns, more preferably from 4 to 8 microns.

To the microcapsules obtained in the present invention, a general water-soluble binder, a latex binder, and a capsule protectant such as cellulose powder, starch particles, talc, etc. are added to obtain a microcapsule coating solution 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 activated clay, phenolic resin, and metal salts of aromatic carboxylic acids.

The performance of the microcapsule sheet for pressure-sensitive recording paper of the present invention was tested using the following color developer sheet. [Adjustment of color developer sheet] [Adjustment of dispersion liquid] 3,5-
15 parts of zinc bis(α-methylbenzyl) salicylate, 120 parts of calcium carbonate, 10 parts of activated clay, 2 parts of zinc oxide
Dispersion (A) which was atomized using a sand mill using 0 parts of sodium hexametaphosphate and 200 parts of water.
I got it. [Adjustment of coating liquid] 1 to 300 parts of dispersion liquid (A)
100 parts of 0% PVA-117 (manufactured by Kuraray) aqueous solution and carboxy-modified SBR latex (manufactured by Sumitomo Naugatac,
SN307) (7 parts as solid content) was added thereto, and water was added to adjust the solid content concentration to 20% to obtain a coating liquid. [
Coating of developer sheet] This coating solution was applied to a 50 g/m 2 base paper using an air knife coater so that the solid content was 5.0 g/m 2 and dried to obtain a developer sheet.

[0020]

[Examples] The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to the Examples.

Example 1 20 g of crystal violet lactone as a coloring agent is dissolved in 250 g of diisopropylnaphthalene. To this oily liquid, 8 g of carbodiimide-modified diphenylmethane diisocyanate (manufactured by Mitsui Toatsu Chemical Co., Ltd., trade name "MDI-LK") as an aromatic polyvalent isocyanate and a biuret form of hexamethylene diisocyanate (manufactured by Sumitomo Bayer Urethane Co., Ltd., trade name "MDI-LK") were added to this oily liquid. Sumidur N3200”) 8
g and 3 g of epichlorohydrin were dissolved to prepare a primary solution. Next, add polyvinyl alcohol (saponification degree 8) to 250 g of water.
A secondary solution was prepared by dissolving 30 g of 8 mol %, polymerization degree of about 500). The primary solution was poured into the secondary solution while vigorously stirring it to form an oil-in-water emulsion at room temperature. When the size of the oil droplets reached 6.0μ, stirring was weakened, and then 220g of water at 20°C was added to the emulsion, and the temperature of the system was gradually raised to 60°C and maintained at this temperature for 90 minutes. Ta. To the capsule liquid thus obtained were added 160 g of a 15% aqueous solution of polyvinyl alcohol, 40 g of carboxy-modified SBR latex in solid form, and 60 g of starch particles (average particle size: 15 μm). Next, water was added to adjust the solid content concentration to 20% to prepare a coating solution. This coating liquid was coated onto a base paper using an air knife coating machine and dried to obtain a microcapsule sheet at a dry weight of 4.0 g/m2.

Example 2 A microcapsule sheet was obtained in the same manner as in Example 1, except that 3 g of phenylglycidyl ether was used in place of 3 g of epichlorohydrin under the conditions for preparing the primary solution.

Example 3 In Example 1, a bisphenol A-based epoxy compound (manufactured by Yuka Ciel Epoxy Co., Ltd., trade name "Epicote 825") was used instead of 3 g of epichlorohydrin under the conditions for preparing the primary solution.
A microcapsule sheet was obtained in the same manner as in Example 1 except that 1 g of the microcapsule sheet was used.

Example 4 In Example 1, 8 g of polymethylene polyphenylisocyanate (manufactured by Nippon Polyurethane Co., Ltd., trade name "Millionate MR200") was used instead of 8 g of carbodiimide-modified diphenylmethane diisocyanate under the conditions for preparing the primary solution.
A microcapsule sheet was obtained in the same manner as in Example 1 except that .

Example 5 The same procedure as in Example 1 was carried out except that 8 g of polymethylene polyphenylisocyanate was used in place of 8 g of carbodiimide-modified diphenylmethane diisocyanate and 3 g of phenyl glycidyl ether was used in place of 3 g of epichlorohydrin under the conditions for preparing the primary solution. A microcapsule sheet was obtained in the same manner as in Example 1.

Example 6 20 g of crystal violet lactone as a coloring agent is dissolved in 250 g of diisopropylnaphthalene. To this oily liquid, 8 g of carbodiimide-modified diphenylmethane diisocyanate (manufactured by Nippon Polyurethane Co., Ltd., trade name "Millionate MTL") was added as an aromatic isocyanate, and an isocyanurate form of hexamethylene diisocyanate (
Manufactured by Nippon Polyurethane Co., Ltd., product name "Coronate EH") 8
Butylene oxide adduct of ethylenediamine as an alkylene oxide adduct of g and amine (number of moles of butylene oxide added to ethylenediamine: 16.8
mole, molecular weight 1267) 3g and epichlorohydrin 6g
A primary solution was prepared by dissolving. Next, add polyvinyl alcohol (saponification degree 88 mol%, polymerization degree approximately 5%) to 250g of water.
00) was dissolved to prepare a secondary solution. The primary solution was poured into the secondary solution while vigorously stirring it to form an oil-in-water emulsion at room temperature. When the size of the oil droplets reached 6.0 μm, the stirring was weakened, and then 220 g of water and 1.0 g of tetraethylenepentamine were added to this emulsion, and the mixture was stirred at room temperature for 15 minutes. After that, the temperature of the system was raised to 60℃, and at this temperature 90℃
I kept it. Using the microcapsule liquid thus obtained, a microcapsule sheet was obtained in the same manner as in Example 1.

Comparative Example 1 A microcapsule sheet was obtained in the same manner as in Example 1 except that epichlorohydrin was not used in the conditions for preparing the primary solution.

Comparative Example 2 A microcapsule sheet was obtained in the same manner as in Example 4 except that epichlorohydrin was not used in the preparation conditions for the primary solution.

Comparative Example 3 A microcapsule sheet was obtained in the same manner as in Example 6 except that epichlorohydrin was not used in the preparation conditions for the primary solution.

[0030]Evaluation tests were conducted on the combinations of the above-mentioned microcapsule sheets and color developer sheets as pressure-sensitive recording sheets, and the results are shown in Table 1. The evaluation test was conducted using the following method. 1) Color development test Layer each microcapsule sheet with a color developer sheet.IBM
A lowercase letter m was printed continuously using a 6747 type electronic typewriter to develop color. One day after color development, print density D (typewriter) in the visible region was measured using a Macbeth RD-918 type densitometer. 2) Solvent resistance test Each microcapsule sheet was immersed in ethyl acetate for about 1 second, dried naturally, and then layered with a color developer sheet at 300 kg/cm.
A weight of 2 was applied to develop color. Furthermore, a fresh sample that was not subjected to the above solvent treatment was similarly colored. Macbeth RD-
The concentration in the visible region was measured using a Model 918 densitometer, and the concentration ratio of the solvent-treated sample to the fresh sample was evaluated. 3) Heat resistance test Each microcapsule sheet was placed on a hot plate at 180°C.5.
After contacting for 0 seconds, overlap with color developer sheet 300kg
/cm2 was applied to develop color. Furthermore, a fresh sample that was not subjected to the above heat treatment was also colored in the same manner. Macbeth R
The concentration in the visible region was measured using a D-918 type densitometer, and the concentration ratio of the heat-treated sample to the fresh sample was evaluated. The results obtained are shown in Table 1.

[0031]

[Table 1]

[0032]

[Effects of the Invention] As is clear from the results in Table 1, the pressure-sensitive recording sheet using the microcapsules of the present invention has superior solvent resistance and heat resistance compared to the comparative one. , has very good performance and is also suitable for NIP.

Claims (2)

[Claims] Claim 1: A microcapsule for a pressure-sensitive recording sheet containing a solution of an electron-donating coloring agent dissolved in a hydrophobic liquid as a core material, wherein the microcapsule wall is made of an aromatic polyvalent isocyanate and a fatty acid. A microcapsule for a pressure-sensitive recording sheet, which is formed from a group-based polyvalent isocyanate and an epoxy compound, and is characterized in that diphenylmethane diisocyanate and/or polymethylene polyphenylisocyanate modified with carbodiimide are used as the aromatic-based polyvalent isocyanate. 2. The microcapsule for a pressure-sensitive recording sheet according to claim 1, wherein the wall of the microcapsule is formed of an aromatic polyvalent isocyanate, an aliphatic polyvalent isocyanate, an epoxy compound, and a polyvalent amine.