DE2735093A1 - COLOR DEVELOPING SHEETS FOR PRESSURE SENSITIVE OR HEAT SENSITIVE COPY PAPERS - Google Patents

Description

Color developing sheets for pressure-sensitive or heat- sensitive copier papers

This invention relates to color developing sheets for pressure sensitive ones or heat-sensitive copier papers of high economic importance, preferred as a color developer a salicylic acid derivative, a hydroxynaphthoic acid derivative or one of their salts with polyvalent metals is used and essentially as a binder a latex modified with carboxyl groups is used.

Color developing sheets for pressure sensitive or heat sensitive Copy papers are known in which a salicylic acid derivative or a similar product is used as a color developer is used and a latex modified with carboxyl groups is used as a binder to make the color developer to bind tightly to the base sheet. Examples of suitable carboxylated latices are those with carboxyl groups modified styrene-butadiene copolymers, methyl methacrylate-butadiene copolymers and vinyl acetate polymers or copolymers called.

With such a combination of the color developer and the binder, the color developer can be bound inside or on the surface of the bast sheet. For example, it is possible to add the binder in a solution to the pulp slurry together with the solid fine-grained or emulsified color developer at the same time as the start of papermaking. The grains of the color developer are quickly retained in the layer of the base sheet, or the binder is dispersed in water together with the grainy color developer and applied by impregnation or applied in an ordinary size press or similar feeder,

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to fix the granular developer inside or on the surface. In these modes of operation, however, there is no uniform one Distribution of the color developer in the aqueous medium becomes possible and, depending on the circumstances, the stability becomes the aqueous solution adversely affected, the viscosity of the coating solution decreased, making the suitability as a coating agent is decreased, with the result that the color-developing sheets in which the fine-grain color developer is distributed, are not uniform in their interior or on the surface of the base sheet. These shortcomings are in the Technique well known.

It has therefore been proposed to solve this problem, a water-soluble substance such as casein, starch or Dextrin (Japanese laid-open specification 51716/1973, Japanese laid-open specification 37711/1974) to use and the Add a surfactant to color developer.

However, it has been found that in the large-scale manufacture of color developing sheets for pressure sensitive Papers over a long period of time the known measures are not suitable for overcoming such difficulties were not even if well known carboxyl group-containing modified latices can be used.

It has been found to be particularly disadvantageous that when water-soluble high molecular substances are added to color developers, the viscosity of the coating solution increases significantly, making it impossible to substantially increase the solids content of the coating solution, thereby reducing productivity substantially. On the other hand, in the case of adding a surface active agent, the foaming of the coating solution greatly increases, whereby the surface of the coated sheet and the distribution of the color developer on the surface of the sheet become irregular , so that the copying

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keep duplications are discontinuous and unsatisfactory. For this reason, the addition is in such cases a defoamer required. However, it is currently difficult to obtain a water-soluble defoaming agent ordinary emulsion type defoaming agents or solid defoaming agents are occasionally used, whereby an increased tendency to form so-called fish eyes can be observed on the coated sheet, and thereby also lowering the quality of the color developing sheets.

It has now been found that a modified by carboxyl groups Latex of a very special composition is suitable for the described difficulties with color-developing Overcome scrolling. When using this latex as a binder for the color developer, it is not necessary to use a to add a water-soluble high molecular substance or a surface active agent to the color developer as the color developer in combination with this latex it is in constant and uniform dispersion in an aqueous medium and the coating composition has excellent viscosity stability and low viscosity.

The invention therefore relates to color-developing sheets for pressure-sensitive or heat-sensitive copier papers, in which a latex of a copolymer modified with carboxyl groups is used as a binder for the developer , the invention being characterized in that the latex copolymer is firstly 30 to 55% by weight of 1,3-butadiene, secondly, 0.5 to 10% by weight of an ethylenically unsaturated one Contains monocarboxylic acid or dicarboxylic acid and thirdly 35 to 69.5% by weight of another monoolefinic monomer, the proportion (gel content) of the copolymer which is insoluble in benzene is in the range from 91 to 99.5% by weight.

The developers preferred in the invention are the salicylic acid derivatives , salts of the salicylic acid derivatives with a

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polyvalent metal, the hydroxynaphthoic acid derivatives and salts of hydroxynaphthoic acid with polyvalent metal. the Color developers can be used in the interior of the base sheet or on its surface with the aid of the invention special carboxylated latex.

Typical examples of the preferred color developers are

following connections:

6-phenylsalicylic acid,

5-benzylsalicylic acid,

5- (4-hydroxyphenyl) salicylate, 4,4 · -dihydroxy-3,3'-dicarboxydiphenylmethane, 3-methyl-5-phenyl salicylate,

4- (2'-p-chlorophenyl) isopropyl-S-cyclohexyl salicylate,

5- (p-nitrophenyl) salicylate,

4- (p-nitrophenyl) salicylate,

1,4-dihydroxy-2,3-dicarboxynaphthalene, 2-hydroxy-5-methyl-l-naphthoic acid, l-hydroxy ^ -dicarboxymethyl ^ -naphthoic acid,

2-hydroxy-5- (p-tertiary-butyl) phenyl-1-naphthoic acid,

2-hydroxy-5-cyclohexyl-1-naphthoic acid,

2-hydroxy-4- (4'-carboxy-3-hydroxyphenyl) -1-naphthoic acid,

5- (5-carboxynaphthyl) -2-hydroxy-1-naphthoic acid, 1,4-dihydroxy-3-benzoyl-2-naphthoic acid, l-hydroxy-o-bromo ^ -naphthoic acid, 1,4-dinitro-3-hydroxy-2-naphthoic acid, 3-hydroxy-4-allyl-2-naphthoic acid, 3-benzoyl-4-phenylsalicylate, p- (3'-carboxy-4-hydroxyphenyl) benzenesulfonate,

4,4'-dihydroxy-3,3'-dicarboxy-5-5 ^! -dimethyldiphenyl,

4-acetoxy-4-hydroxy-3,3'-dicarboxydiphenyl, 5- (p-aminobenzyl) salicylate,

S-benzyl-e-aminosalicylate,

3- (p-methyl) phenyl 4- (4-methyl) cyclohexyl salicylate, 5- f (4-ethoxycarbonyl) phenyl salicylate,

4- (2-phenyl) isopropyl-5-tetrahydroxynaphthyl salicylate,

4- (5-methylnaphthyl) salicylate,

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3- (2-hydroxy-1-naphthyl) methylate, 2-hydroxy-1-benzyl-3-naphthoic acid and 313'-dicarboxy-2,2'-dihydroxy-1,1'-dinaphthylmethane.

As salts of polyvalent metals come in particular those these organic acids with metals such as zinc, magnesium, aluminum, cadmium, lead, titanium, calcium, cobalt, Nickel and manganese into consideration.

In general, the viscosity, the viscosity stability and the colloidal properties of the coating solution depend on the type and amount of the emulsifier used for latex production. In the case of the latices of polymers modified with carboxyl groups, it is well known that these properties depend on the type and amount of the ethylenically unsaturated carboxylic acids used. In addition, the benzene-insoluble fraction (gel content) of the carboxylated latex also has an influence on the viscosity of the coating solution and its stability. When the gel content of the copolymer is in the range of 91 to 99 »5, the latex has low viscosity in addition to good binding ability and retention for the color developer inside or on the surface of the paper, and the viscosity stability is excellent. It is also surprising that copies made with the aid of these color-developing sheets on pressure-sensitive copier paper are continuous and brightly colored and that the aging properties of such copies are also significantly improved in terms of resistance to sunlight, moisture and heat. In the copolymer latices according to the invention, the butadiene is present in amounts of 30 to 55 wt.%, Preferably 35 to 50 wt.% Before. If less than 30% by weight of this monomer is used, a hard, brittle and non-film-forming copolymer results, which has only poor bond strength. On the other hand, if more than 55 % by weight of butadiene is used, the copolymers are rubbery materials,

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which are too soft for the purpose under consideration here and tend to stick to the roller when the coated papers are roller-treated. They also have one poor water resistance. Furthermore, even at contents of more than 50% by weight of butadiene, it can be observed that the time for color development becomes longer after the application of pressure. The butadiene content used in the invention consequently represents the optimum in terms of color development and other copying properties for pressure-sensitive ones Copy papers.

Examples of suitable ethylenically unsaturated mono- or dicarboxylic acids, which are used alone or as a mixture are acrylic acid, methacrylic acid, maleic acid, itaconic acid, fumaric acid and cinnamic acid. This component of the copolymer is used in amounts of 0.5 to 10% by weight, based on the polymerizable monomers. A latex copolymer, which contains more than 10% by weight of these acids leads to an undesirable increase in viscosity. The opposite is the case of a copolymer with less than 0.5% by weight of the acid component associated with the fact that it presents difficulties to achieve the desired viscosity, pigment stability and mechanical stability, and that the bond strength of the with it produced coated paper is poor, so that pluckers may occur when writing or printing.

The other monoolefinic monomers used in the invention include vinyl aromatic monomers such as styrene, alpha-methyl styrene and vinyl toluene, also alkyl esters of olefinically unsaturated carboxylic acids such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and 2-hydroxyethyl acrylate. These monomers can be copolymerized with butadiene and the olefinically unsaturated carboxylic acids and are used in amounts of 35 to 69.5% by weight, based on the total weight of the monomers. Among these monomers are particularly

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those preferred, the carboxylated styrene-butadiene polymers, Methyl methacrylate-butadiene copolymers or styrene methyl methacrylate-butadiene copolymers form.

The latices of carboxylated copolymers used in the invention can be prepared for emulsion polymerization by known methods produce. Preferred emulsifiers are anionic emulsifiers, such as ester salts of reaction products from sulfuric acid and higher alcohols, alkyl allyl sulfonates, alkyl naphthalene sulfonates and derivatives thereof. These anionic emulsifiers can also be used in combination with non-ionic surfactants, e.g. Polyoxyethylene alkyl ethers and polyoxyethylene alkyl phenol ethers. Examples of polymerization initiators are inorganic ones Called peroxides, such as hydrogen peroxide and persulfates, or organic peroxides, such as lauryl peroxide, diisobutylbenzoyl peroxide and cumene hydroperoxide, also the so-called redox catalysts, in which an oxidizing catalyst used in combination with a reducing agent such as sodium disulfite, sulfonates or formaldehyde. In the Polymerization, typical chain transfer agents can also be used, such as mercaptans, e.g. n-dodecyl mercaptan, t-dodecyl mercaptan and t-hexadecyl mercaptan, chlorides, such as carbon tetrachloride or methylene chloride, bromides, such as carbon tetrabromide and ethylene bromide and hydrocarbons such as pentaphenylethane. The polymerization can be discontinuous, be carried out semi-continuously and continuously. The preferred polymerization temperatures are in the range from 50 to 100 ° C.

The gel content, or the content of the insoluble in benzene, can be influenced by the yield, the polymerization temperature, the type and amount of chain transfer agent and by the composition of the carboxylated latex copolymer .

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As already stated, the carboxylated latex polymer works best in color-developing sheets, if it is with at least one of the named color developer from the group of the salicylic acid derivatives, the salts of polyvalent metals with the salicylic acid derivatives, the hydroxynaphthoic acid derivatives and the polyvalent metal salts are used together with the hydroxynaphthoic acid. It is of course also possible to use the carboxylated latex copolymer to be used in combination with other known color developers, e.g. activated clay or phenolic resins.

Although the color-developing sheets according to the invention are primarily of interest for pressure-sensitive copier papers, however, they can also be used in known heat-sensitive copier papers, for example those according to FIG Japanese Patent Publication 14039/1970.

The invention is explained in more detail in the following examples and comparative experiments. For measuring the physical Properties, the following methods were used: 1. Measurement of the gel content or the insoluble fractions in

benzene

A latex film is applied to a glass plate and allowed to dry at room temperature for a full day and overnight. After that, it is placed in a vacuum dryer at a reduced pressure of 700 mm Hg at a temperature of 50 ° C dried to constant weight (usually 2 to 3 hours).

Weigh 0.25-0.30 g of the dried film precisely (A (g)) in a 300 ml triangular bottle and it will 100 ml of benzene are added. The bottle is tightly closed and its contents are slowly stirred for 24 hours.

By using a hot air dryer, a filter paper (JIS No. 1) is dried at 105 ° C for 40 minutes and is

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then refrigerated and accurately weighed in a dryer (B (g)) »confirming the change in weight of the filter paper is 0.3 mg or less.

The gel portion insoluble in benzene is passed through this filter paper separated and mixed with a small amount of benzene. This insoluble part is put in a hot air oven, the one Has a device to prevent explosions, dried at a temperature of 130 ° C for 40 minutes, cooled and in weighed exactly in a drying device (C (g)).

The gel content is calculated using the following formula: Gel content (%) =

2. Measurement of the viscosity of the coating solution

The viscosity of the coating solution is measured by a BL-type viscometer with a No. 2 rotor at 60 rpm.

3. Viscosity stability of the coating solution (measured with a roller tester)

The coating solution is circulated and passed into a roll tester for 1 hour. The first roller is set to 500 rpm and the second roller to 700 rpm. «The diameter of the first roller is 250 mm, the one the second roller 200 mm. The width of the first and the second roller is 300 mm. After 1 hour has passed the degree of adhesion of the gel on the surface of the roller is observed and the viscosity of the solution, its temperature and the residue measured on a 200 mesh sieve. Summing up these results, the viscosity stability the coating solution detected.

4. Evaluation of pressure-sensitive copier papers: (a) Coloring properties:

Evaluation of the color concentration of the reproduction of letters by typewriters (observation with the eye)

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(b) Resistance to sunlight:

Determined by the degree of decrease in concentration of letters by direct observation with the eye Exposure to sunlight for 4 hours.

(c) Moisture Resistance:

Estimated by the degree of decrease in the color concentration of letters observed with the eye after Stand at 50 ° C in a 90 RH atmosphere.

(d) Heat resistance:

Estimated by the degree of decrease in the color concentration of letters observed with the eye after Stand for 15 hours at a temperature of 100 ° C.

(e) Surface strength:

This is understood to mean the pick resistance of the coated surface, measured with the IGT tester. Applied Printing pressure 35 kg, nib M, black ink from Dai Nihon Ink Co., Ltd., SSG 85; Temperature 20 ° C, humidity 60%.

Examples 1-7 and Comparative Experiments 1-7

I. Carboxylated latex polymers:

In Example 1, 31 parts by weight of butadiene, 63 parts by weight of styrene, 6.0 parts by weight of acrylic acid, 0.01 part by weight of t-dodecyl mercaptan, 0.9 part by weight of sodium hydrogen carbonate, 0.9 parts by weight of potassium persulfate, 0.8 parts by weight of sodium alkylbenzenesulfonate and 150 parts by weight of water placed in a 5 liter autoclave and kept at 65 ° C Reacted for hours with stirring in a nitrogen atmosphere. The conversion of the monomers to the copolymer was 99%.

In comparative experiment 1, 0.5 parts by weight of t-dodecyl mercaptan were used and the. other conditions were the same as in Example 1 to give a carboxylated latex copolymer having a gel content of 69%.

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For the other examples and comparative experiments are the Starting materials for the carboxylated latex copolymers are given in Tables I and II. These raw materials were polymerized under conditions similar to those in Example The symbol * in the column of vinyl aromatic monomers means vinyl toluene.

The pH of the latexes was adjusted to 8 with sodium hydroxide and the latexes were with steam and nitrogen blow through to remove residual monomers. The mean grain diameter of the copolymer was about 1900 Å.

In Tables I and II, in the column for the chain transfer agent t-DDN t-dodecyl mercaptan and n-DDM n-dodecyl mercaptan.

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Table I: Monomer composition for making the carboxylated latex copolymers

Example butadiene vinyl aromatic. Methyl- 2-Hydroxy- Itacone- Fumar- Acryl- Chain Over-

No. Monomeric meth- ethyl-acid acid-carrying acrylate acrylate medium

αο ο co

1 31 63 2 38 55.5 3 39 55 4th 40 56.5 * 5 43 52.5 6th 48 23 7th 53 42

25th

2.5 6.0 t-DDM
0.01 - 3.0 4.0 t-DDM
0.02 - - - CCl ₄
0.8 3.5 - - n-DDM
0.05 3.0 - 1.5. t-DDM
0.01 - 5.0 4.5 CHBr,
O, 3 ³ - - n-DDM
0.04

Comparative experiment
No.

Table II: Monomer composition for the preparation of the carboxylated «! Latex copolymers

Butadiene vinyl aromatic. Methyl meth itacone fumar acrylic chain transfer

Monomeric Acrylate Acid Acid Acid Carrying Agent

1
2
3
H

5
6th

31 38 27 56 43 48 43

63

55.5

70

40.5

52.5

23

46

3.5 3.0

2.5

3.0

6.0 f-DDM
0.5 t
M.
ν.η
I. 4.0 t-DDM
0.5 - §3 *
n-DDM
0.05 1.5 t-DDM
0.6 4.5 CHBr ₃ K)
-j
CO
ir
O
cc
co 11 n-DDM
0.01

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II. Evaluation of the carboxylated latex copolymer in the color developing Pressure sensitive paper sheet 150 parts of water and 16 parts of the carboxylated latex of Example 1 were mixed. To the mixture, 25 parts of 4-phenyl salicylate was added and well dispersed therein with stirring. Then 25 parts of zinc oxide were added again with stirring, a coating pigment being formed. This pigment was applied to a surface of a base sheet weighing 50 g / m 2 in such amounts as that the base sheet had a dry weight of 5 g / m 2. This base sheet became a color developing sheet dried.

Similarly, the carboxylated latices of Examples 2-7 and Comparative Experiments 1-7 were used to make color developer sheets manufactured.

Table III shows the results of measuring the viscosity stability with a roller tester on these coating solutions.

Separately, a coating solution was prepared containing microcapsules in which crystal violet lactone and benzoyl leucomethylene blue had been encapsulated by a dissolution and coacervation process using gelatin and gum arabic. This coating solution was applied to a 50 g / m 2 base sheet and dried. The coated surfaces of the color developer sheets according to Examples 1-7 and Comparative Experiments 1-7 were compared with the coated surfaces containing the capsules mentioned above and written on with a typewriter. The written letters appeared on the color developing sheets, and their resistance to sunlight, moisture resistance, heat resistance and the bonding strength and surface strength of the color developing sheets were examined. The results are summarized in Table IV.

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Table III: Viscosity of the coating solution and its Viscosity stability

Example viscosity of the coating solution (cp)

Viscosity stability *

Gel insoluble in benzene (%)

1 20th 2 25th EO 3 24 0 »
O 4th 26th -Λ
* »* 5 24 O Ο » 6th 21 7th 23

(Ö)

94 92 93 95 97 96 98

Table III (continued)

Comparative experiment

2 α »

° 3

co ^J

o 4

^ 5 ο

σ »6

viscosity
train solution the over-
(cp) Viscosity
stability* Insoluble in benzene
Gel (%) 39 X 69 42 X 71 35 Ο-Δ 88 27
43 0
Δ -χ 97
75 40 X 60

7 Not measured because of the increase in viscosity of the latex (more than 500 cp) '

* Symbol for viscosity stability:

g) good O

χ bad

Table IV: Evaluation of the latices in color developer sheets for pressure sensitive copier papers

example

Color strength of the letters

Resistance to sunlight

Moisture resistance

Heat resistance - surface strength

5
6th
7th

5 5 5 5 5 5 5

4.5

4.5

4.5

5 5 5 5 5 5 4

5 5 5 5 5 5 5

4.5

4.5

Table IV (continued)

Comparative color strength of the resistance, moisture-heat-resistant, surface test Letters against sun resistance

light

13 3 2 34

2 3 3 2 34

3 3.5 3 3 3 2
oo

S 4 3 3 1.5 2 4.5

S 5 3 2 2 3 4 -y

^ 6 3 2 2 24 c

* 7 Not measured due to the increase in viscosity of the latex
~ J (more than 500 cp)

In these ratings, a higher number means a better property.

Claims (3)

Patent claims: Color developing sheets for pressure-sensitive or heat-sensitive copier papers which are used as Binder a latex of a copolymer modified with carboxyl groups is used, characterized in that the latex copolymer firstly has 30 to 55% by weight of butadiene 1,3 »secondly 0.5 to 10% by weight of a Ethylenically unsaturated monocarboxylic acid or dicarboxylic acid and thirdly 35 to 69.5 wt.% Of one contains other monoolefinic monomers, wherein 809807/0646 original inspected the part that is insoluble in benzene (gel content) of the copolymer in the range from 91 to 99.5% by weight lies. 2. Color developing sheets according to claim 1, characterized in that that the other monoolefinic monomer is styrene. 3. Color developing sheets according to claim 1, characterized in that that the other monoolefinic monomer is ethyl acrylate and / or methyl methacrylate. 809807/0646