JPH0441912B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a dye solvent for pressure-sensitive recording paper, and more particularly to a mixture of p-isopropyl biphenyl, diisopropyl biphenyl and m-isopropyl biphenyl in a specific proportion, or a mixture of p-isopropyl biphenyl and diisopropyl biphenyl. A dye solvent for pressure-sensitive recording paper comprising a mixture of the following in a specific proportion. Prior art Pressure-sensitive recording paper develops color when a color former with electron-donating coloring reactivity is dissolved in an organic solvent, encapsulated in microcapsules, and brought into contact with a color former sheet coated on a support. It consists of a color developer sheet with a color developer coated on another support. In recent years, pressure sensitive recording paper has been widely used to replace carbon copy paper or pigment-type back carbon copy paper. Such pressure-sensitive recording paper must have excellent color development, long-term storage stability, and light resistance, and must also be low in toxicity and free from pollution problems. A solvent for dissolving the coloring agent (dye) in pressure-sensitive recording paper is required to meet the following requirements. (1) The color former has high solubility. (2) Do not cause any changes such as decomposition or color development of the coloring agent. (3) It has a fairly high boiling point and does not transpire during heat drying processes or at high temperatures. (4) It should not be eluted into water during encapsulation. (5) High color development speed and color density, and high color stability after color development. (6) Stable against light, heat and chemicals. (7) The viscosity should be low so that when the capsule is ruptured, the fluid can flow freely from inside the capsule. (8) Substantially free of odor. (9) It should be safe and have low toxicity to the human body. (10) Good biodegradability and no environmental pollution. The following solvents have been proposed as dye solvents for pressure-sensitive recording paper that meet these requirements. Pressure-sensitive recording paper characterized in that at least one of alkylated biphenyl or alkylated terphenyl having an alkyl group having 1 to 12 carbon atoms is used alone or in combination with other solvents as a solvent for the coloring agent (however, alkylated biphenyl (The number of alkyl groups is 1 to 4 in alkylated terphenyl, and the number of alkyl groups is 1 to 6 in alkylated terphenyl, and two or more alkyl groups may be the same or different.) (Japanese Patent Publication No. 49-21608), for example

65% or more of isopropyl biphenyl, 25% or less of polyisopropyl biphenyl and biphenyl 10 represented by [formula]
There is a recording sheet material (Japanese Patent Publication No. 37528/1983) coated with microcapsules containing a dye precursor dissolved in a solvent containing a dye precursor of less than 1%. In addition, as a method for producing alkyl biphenyl, in the presence of 0.5 to 10% by weight of a silica-alumina catalyst, a zeolite catalyst, or a mixed catalyst of both based on biphenyl, at a temperature of 180 ° C. or higher,
m-, p characterized in that 0.5 to 5 mol of lower olefin is brought into contact with 1 mol of biphenyl.
A method for producing alkyl biphenyl rich in substituents at the -position (Japanese Patent Publication No. 56-156222) is known. In particular, isopropylbiphenyl, which is the main constituent of the dye solvent for pressure-sensitive recording paper disclosed in Japanese Patent Publication No. 54-37528, is an isomer mixture of compounds represented by the following structural formula. (The isopropyl group is attached to the benzene ring in the ortho, meta or para position). In addition, the special public service 1977-
37528, the composition of a suitable dye solvent for pressure-sensitive recording paper is approximately 50% m-isopropyl biphenyl, 30% p-
Isopropylbiphenyl, 25% polyisopropylbiphenyl and 0.5% biphenyl. It is also synthesized by commercially available isopropyl biphenyl and Friedel-Crafts alkylation of biphenyl (Industrial and
Engineering Chemistry Product Research and
Development Vol. 8, pp 239-241, 1969) Isopropylbiphenyl is a mixture of meta and para isomers (meta: para: isomers (weight ratio ) = approx. 2:
1). In recent years, with the spread of recording paper, pressure-sensitive recording paper can be used, for example, in cold regions where the ambient temperature is below 0°C, or in hot and humid environments where the ambient temperature is approximately 40 to 50°C and the relative humidity is approximately 80% or higher. There are many opportunities for underground transportation and long-term storage. Particularly, pressure-sensitive recording paper is used in outdoor facilities such as winter gas stations in environments with low temperatures of 0° C. or lower. In such a low-temperature environment, the dye solvent used may crystallize, the time from when a record is made until the record clearly appears is extremely long, and even if color develops, the written record may The problem has arisen that it cannot be put to practical use because it is so thin that it cannot be read. Therefore, there is a need to provide a dye solvent for pressure-sensitive recording in which almost no crystals of the dye solvent occur even at 0° C., and which has a color development rate of at least 40% at the initial stage of color development approximately 30 seconds after recording. . Furthermore, from the viewpoint of manufacturing and storage of pressure-sensitive recording paper, it is strongly desired to provide a dye solvent for pressure-sensitive recording paper that is substantially odorless. This odor problem occurs during the manufacturing process of pressure-sensitive recording paper, when recording paper material coated with microcapsules on a support is dried and then cut. That is, the recording paper material is 40 to 50
When cutting is carried out at a relatively high temperature such as ℃, the odor of the dye solvent flowing out from the microcapsules destroyed by cutting gives an unpleasant feeling to the operator. Furthermore, during the cutting process or manufacturing process, the dye solvent may adhere to clothes or hands. Even if the attached dye solvent is washed with detergent, the odor remains and causes discomfort. Furthermore, since the recorded paper is collected and stored in one place for a relatively long period of time, the odor emitted from the large amount of recorded paper can cause discomfort. Considering the problem of odor, the above-mentioned conventionally proposed isopropyl biphenyl has a rather strong odor and is not suitable as a dye solvent for pressure-sensitive recording paper. This isopropylbiphenyl is an isomer mixture with O-isopropylbiphenyl, m-isopropylbiphenyl and p-isopropylbiphenyl, or an isomer mixture with p-isopropylbiphenyl whose main component is m-isopropylbiphenyl. It is. O-isopropylbiphenyl exhibits an unpleasant odor, and m-isopropylbiphenyl also has an odor. On the other hand, although p-isopropylbiphenyl is almost odorless and has excellent dye solubility, it has a relatively high melting point, so it has the disadvantage that crystals tend to precipitate at low temperatures. Therefore, it is almost odorless and can be used at low temperatures (e.g. 0
It is desired to provide a dye solvent for pressure-sensitive recording paper that exhibits excellent initial color development and hardly precipitates crystals even at temperatures (°C). In order to provide a dye solvent for pressure-sensitive recording paper having the above-mentioned required properties, as a result of intensive research by the present inventors, 40 to 75% by weight of p-isopropylbiphenyl,
5-40% by weight of diisopropylbiphenyl and m-
A solvent consisting of a mixture of 20% by weight or less of isopropylbiphenyl or a mixture of 60 to 75% by weight of p-isopropylbiphenyl and 25 to 40% by weight of diisopropylbiphenyl is almost odorless and hardly precipitates crystals even at low temperatures. Furthermore, it was discovered that the dye solvent for pressure-sensitive recording paper satisfies all of the above-mentioned conditions, and based on this knowledge, the present invention was accomplished. Means for Solving the Problems The solvent of the present invention contains 40 to 75% p-isopropyl biphenyl (hereinafter abbreviated as P-MIPB) and 5 to 40% diisopropyl biphenyl (hereinafter abbreviated as DIPB).
Weight% and m-isopropylbiphenyl (hereinafter m
- A mixture of solvents consisting of 20% by weight or less (abbreviated as MIPB) or P-MIPB60 to 75% by weight and DIPB25 to
It is a mixed solvent consisting of 40% by weight. The mixing ratio of m-MIPB, p-MIPB, and DIPB, which are the constituent components of the dye solvent for pressure-sensitive recording paper of the present invention, is within the range shown by points A, B, C, and D in the triangular diagram shown in FIG. be. A in Figure 1 is m-MIPB 20% by weight, p-
It is a point of 75% by weight of MIPB and 5% by weight of DIPB, and B
m-MIPB 0% by weight, p-MIPB 75% by weight and
DIPB25 wt% point, C is m-MIPB0 wt%, p-MIPB60 wt% and DIPB40 wt% point, and D is m-MIPB20 wt%, p-MIPB20 wt% point.
The points are 40% by weight of MIPB and 40% by weight of DIPB. Such mixed solvents are almost odorless,
Almost no crystals precipitate even at low temperatures, for example 0℃, and low-temperature color development, for example, the initial color development rate 30 seconds after recording at -5℃ is a substantial value (40℃).
%), it is useful as a dye solvent for pressure-sensitive recording paper. The preferred mixing ratio of the mixed solvent of the present invention is within the range shown by points a, b, c, and d in Figure 1, where a is m-
MIPB 20% by weight, p-MIPB 70% by weight and
b is the point of DIPB 10% by weight, b is the point of m-MIPB 0% by weight, p-MIPB 70% by weight, DIPB 30% by weight, c is the point of m-MIPB 0% by weight, p-MIPB 65% by weight and DIPB 35% by weight. Yes, d is m-
MIPB 20% by weight, p-MIPB 45% by weight and
The point is DIPB 35% by weight. If the content of m-MIPB exceeds 20% by weight, it is not preferred because it causes problems in terms of odor. p-
If the content of MIPB exceeds 75% by weight, crystals tend to precipitate at low temperatures, which is not preferable. Also,
If DIPB exceeds 40% by weight, low-temperature color development becomes insufficient, which is not preferable. It is one of the constituent components of the mixed solvent of the present invention.
DIPB is 2,2'-, 2,3'-2,4'-, 3,3'-,
Although it is a mixture of isomers such as 3,4'- and 4,4'-, the effects of the present invention are not limited by the type of isomer of DIPB. The dye solvent for pressure-sensitive recording paper of the present invention may be any of the known dye solvents for pressure-sensitive recording paper, as long as it does not impair the properties of being almost odorless, excellent low-temperature color development, and hardly precipitating crystals at low temperatures. , for example diisopropylnaphthalene, hydrogenated terphenyl and butyl biphenyl, or diluents of dye solvents for pressure-sensitive recording paper, such as dodecylbenzene and kerosene. The mixed solvent of the present invention includes m-MIPB, P-
It can be obtained by mixing MTPB and DIPB within the above mixing ratio range, or it can also be produced by the method below. (1) Biphenyl and propylene are reacted at a temperature of 120 to 260°C in the presence of a silica-alumina catalyst to propylate biphenyl, and the resulting reaction product is distilled under reduced pressure to give an average boiling point of 138 to 138. A method consisting of separating the fraction at 149°C. (2) Biphenyl is propylated by reacting biphenyl and propylene at a temperature of 50 to 90°C in the presence of an aluminum chloride catalyst, and the resulting reaction product is distilled under reduced pressure to produce p-MIPB.
A method consisting of separating and purifying DIPB, and separately distilling and purifying DIPB, and then mixing it with purified p-MIPB at a predetermined ratio. In the process of propylating biphenyl in the presence of a silica-alumina catalyst, the silica-alumina catalyst is used in the transalkylation of a naphthalene-diisopropylnaphthalene mixture at 280°C. - Catalyst, preferably 0.2 Kg/Hr.Kg - Catalyst, and () retains 90% or more of its initial activity even after treatment with a naphthalene-diisopropylnaphthalene mixture 100 times the weight of the catalyst. , silica-alumina catalysts are preferred. Examples of the silica-alumina catalyst having the above characteristics include X-632NH and N-632L manufactured by JGC Chemical Industries, Ltd. The reaction temperature for propylation is 120-260°C, preferably 150-240°C. If the reaction temperature is less than 120°C, the reaction rate is too slow to be practical. Further, if the reaction temperature is 260° C. or higher, a decomposition alkylation reaction is observed and the reaction product exhibits an odor, which is not preferable. The pressure-sensitive recording paper using the solvent of the present invention is a p-
MIPB40-75% by weight, DIPB5-40% by weight and m-
MIPB20wt% or less solution or p-MIPB60-75
It is characterized by being coated with microcapsules containing a solvent of 5 to 40% by weight and DIPB. Therefore, any methods known to those skilled in the art can be applied without being limited to the encapsulation method, the color forming agent (dye) and color developer used, the method of preparing slurry thereof, the method of applying the slurry, etc. For example, various encapsulation methods include a method using coacelvation disclosed in U.S. Patent No. 2800457 and No. 2800458, a method using interfacial polymerization disclosed in British Patent No. 990443 and U.S. Patent No. 3287154, etc. methods are available. Examples of the coloring agent (dye) include triphenylmethane compounds, diphenylmethane compounds, xanthene compounds, thiazine compounds, and spiropyran compounds. Furthermore, acidic substances used as color developers include acid clay, activated clay,
activated clay materials such as attaparsiaite, bentonite, zeolite etc. or phenolic resins,
Examples include organic acidic substances such as acid-reactive phenol-formaldehyde novolac resins, metals of aromatic organic acids, and the like. Effects of the Invention The dye solvent for pressure-sensitive recording paper of the present invention is almost odorless, has excellent dye solubility, and can be used at low temperatures (0.
C), the crystals hardly precipitate, and the above-mentioned requirements for a dye solvent for pressure-sensitive recording paper are satisfied. Furthermore, the pressure-sensitive recording paper using the solvent of the present invention has an initial color development rate of 40% or more 30 seconds after recording at a low temperature (-5°C), and can be used practically even in cold regions. . EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to the Examples. [Catalytic activity measurement method] Apparatus: Glass beads with a diameter of 2 mm to support the catalyst at the bottom of a stainless steel reaction tube with an inner diameter of approximately 25 mm.
Fill with 10 ml and fill with 25 ml of catalyst on top.
Furthermore, 20 ml of 2 mm diameter glass beads are filled on top of it as a preheating zone. Heating is performed externally with an electric heater, and the temperature is measured with a thermocouple inserted into the reaction tube. Method An equimolar mixture of naphthalene and diisopropylnaphthalene (mixture of isomers) is heated to approximately 60°C to dissolve the naphthalene. This mixture is supplied from the top of the reactor at a constant flow rate, and the catalyst layer is heated to 280℃.
to continuously react naphthalene and diisopropylnaphthalene. The reaction liquid flowing out from the bottom of the reaction tube is cooled to below 100°C, and if necessary, sampled and analyzed by gas chromatography. The flow rate is such that the initial reaction rate of naphthalene is 10-20%
Set it so that In addition, the naphthalene and diisopropylnaphthalene used as raw materials are those containing few components that impair catalyst activity, such as sulfur and nitrogen compounds. Evaluation Approximately 5 times the weight of the catalyst was naphthalene from the start of the reaction.
The naphthalene conversion rate (X ₀ ) is determined from the analysis results of the product at the time when the diisopropylnaphthalene mixture is reacted, and the initial activity of the catalyst is determined using the following equation. Initial activity (A ₀ ) = (W _N ) × (X ₀ )/(W _C ) (where, W _C indicates the catalyst loading amount (g), and W _N indicates the naphthalene supply rate (g/Hr). ) Continuing the reaction, the conversion rate of naphthalene (X 100 ) at the time when 100 times the weight of the catalyst was reacted with the naphthalene conversion rate (X ₁₀₀ ) was determined from the analysis results of the product, and the catalyst activity was calculated using the following formula. Find the retention rate. Activity retention rate (Ap) = (X ₁₀₀ ) / (X ₀ ) × 100 Catalyst activity test example Silica alumina catalyst [X-
632HN (3 mmφ pellets)] was filled into a reaction tube, and an equimolar mixture of naphthalene-diisopropylnaphthalene was supplied at 250 ml/Hr. (245 g/Hr.) to carry out a transalkylation reaction at 280°C. The reaction solution was collected 30 minutes and 10 hours after the start of the reaction, and analyzed by gas chromatography. The results are as follows. X ₀ = 17.0% X ₁₀₀ = 16.2% A _P = 95.3% Also, the initial activity is W _N = 92.2 g/Hr _.
From =25g, it is as follows. A ₀ = 92.2 x 0.17/25 = 0.63 Kg/Hr.Kg - Catalyst Example 1 In a stainless steel autoclave with a capacity of 1.5, 1000 g of biphenyl and the silica alumina catalyst used in the catalyst activity test example (manufactured by JGC Chemical Co., Ltd., X-
632HN) was charged and heated to raise the temperature inside the reactor to 70°C or higher to melt the biphenyl. Next, start stirring and further heat to bring the temperature inside the reactor to 240°C.
℃. Introducing propylene gas from a cylinder,
The pressure was maintained at about 2 Kg/cm ² ·G, and the propylation reaction was carried out at 240°C. During the reaction, the reaction solution was sampled from time to time to analyze its composition, and the average degree of propylation was approximately
Propylene gas supply was stopped when it reached 1.0. The composition of the cooled and collected reaction solution is as follows. Table-1 Ingredients Composition (mol%) Biphenyl 27.8 o-isopropylbiphenyl (O-MIPB)
6.0 m-MIPB 18.7 p-MIPB 22.1 DIPB 23.9 Triisopropylbiphenyl, etc. (TIPB) 1.5 The reaction product thus obtained was carefully fractionated at 140°C under a reduced pressure of 5 mmHg. The composition of the obtained fraction is as follows. Table 2 Components Composition (% by weight) m-MIPB 15.0 p-MIPB 71.9 DIPB 13.1 Comparative Example 1 A propylation reaction of biphenyl was carried out in the same manner as in Example 1. The obtained reaction product was heated to 5 mmHg.
Fractional distillation was carried out at 141-150°C under reduced pressure. The composition of the obtained fraction is as follows. Table 3 Components Composition (wt%) m-PIPB 0.8 p-MIPB 47.6 DIPB 51.6 Examples 2 to 4 and Comparative Example 2 Using the same silica alumina catalyst and the same method as in Example 1, the compounds shown in Table 4 were The propylation reaction of biphenyl was carried out at the reaction temperature. The obtained reaction product was distilled in the same manner as in Example 1 to obtain p-MIPB.
A fraction containing as the main component was obtained. Table 4 shows the composition of the reaction product and the fraction.

[Table] Comparative Example 3 (Reaction using aluminum chloride catalyst) 500 g of biphenyl was charged into a glass autoclave with a capacity of 1, and the temperature inside the reactor was raised to 80°C to melt it. Next, after adding 14 g of anhydrous aluminum chloride as a catalyst, the autoclave was sealed and stirring was started. Introduce propylene using a cylinder, adjust the reactor temperature to 100-110℃, and increase the pressure to approximately 1Kg/kg.
cm ² ·G, and the reaction was continued until the average degree of alkylation was approximately 1. After the reaction was completed, the reaction product was thoroughly washed with hydrochloric acid and pure water to remove the catalyst. The reaction product thus treated was carefully fractionated using a precision distillation column. The compositions of the obtained reaction product and fraction are as follows.

[Table] Example 5 (Preparation of dye solution for pressure-sensitive recording paper) 100 ml of the solvent obtained in Example 1 was heated to 150°C, and while stirring, CVL (blue dye manufactured by Hodogaya Chemical Industry Co., Ltd.) was added. ) 30g was dissolved. Next, this solution was placed in a constant temperature bath at 20°C and left to stand, and the concentration of CVL in the solution was measured economically.
The results are shown in the table below. From Table 6, it is clear that the extremely high concentration state can be stably maintained for a long period of time. Table 6 Elapsed time 1st day 7th day 14th day Dye concentration in solution 19.6 13.9 10.8 (g/100ml) Example 6 Preparation of microcapsules Using the dye solvent for pressure-sensitive recording paper obtained in Example 5, Capsules are prepared in the following manner. 630 g of melamine and 1620 g of formalin (37% formaldehyde aqueous solution; the same applies hereinafter) adjusted to pH=9.0 with a 2% NaOH aqueous solution were mixed and heated to 70°C.
Immediately after the melamine was dissolved, 2250 g of water was added and the mixture was stirred for 3 minutes to obtain a melamine formaldehyde prepolymer aqueous solution. Mix 1,460 g of formalin adjusted to pH=8.5 with triethanolamine and 600 g of urea, and heat at 70°C.
A urea formaldehyde prepolymer aqueous solution was obtained by reacting for a period of time. 1620g of 37% formaldehyde aqueous solution and 600g of urea
After stirring, adding triethanolamine to the mixture and adjusting the pH to 8.8, the mixture was heated to 70°C.
The reaction was allowed to proceed for 30 minutes. 400g of this reaction mixture was taken, 24g of water and 30g of tetraethylenepentamine were added thereto, and the pH was adjusted to 3 with hydrochloric acid at 15°C while stirring at a temperature of 70°C. 10 in the reaction mixture as the pH decreases as the reaction progresses.
% caustic soda aqueous solution was added to adjust the pH to 3, the temperature was lowered to 55°C, and the reaction was continued. When the viscosity of the reaction mixture reached 200 cps, it was neutralized with a 10% caustic soda aqueous solution, and 4000 g of water was added to obtain an aqueous solution of an aqueous cationic urea resin. 1000 g of melamine prepolymer, 500 g of urea prepolymer, 1580 g of the above-mentioned cationic urea resin,
After adjusting the mixed solution of 620 g of water and 10 g of triethanolamine to PH = 5.2 with a 10% aqueous citric acid solution,
30 g of a 10% Neoberex aqueous solution (surfactant manufactured by Kao Atlas Co., Ltd.) was added to prepare Solution A. Separately CVL (Blue dye manufactured by Hodogaya Chemical Industry Co., Ltd.) 500
g was dissolved in 9,500 g of the solvent of Example 1 to obtain liquid B. 1000 ml of Solution B was emulsified in Solution A using a homogenizer so that the particle size was 2 to 8 μm, and then a 1% aqueous citric acid solution was added to the emulsion with gentle stirring while maintaining the temperature at 30° C. to adjust the pH to 3.6. After this emulsion was stirred for 1 hour, 2000 ml of water was added. After a further 3 hours, 20% citric acid was added to adjust the pH to 3.0 and stirring was continued for 20 hours to obtain a microcapsule slurry. Preparation of pressure sensitive recording paper 300g of microcapsules thus obtained
was added to 600 ml of a separately prepared 10% solution of PVA (polyvinyl alcohol manufactured by Kuraray Co., Ltd.) and stirred thoroughly to obtain a dispersion. This dispersion was applied to paper with a basis weight of 45 g/m ² so that the amount of microcapsules coated was 22 g/m ² . This was combined with a color developer paper coated with a color developer material containing a condensate of paraphenylphyenol and formaldehyde as the main color developer by a conventional method to obtain a pressure-sensitive recording paper. The resulting pressure-sensitive recording paper was colored using an Olivetsu Typewriter under normal conditions, and then left in a dark place for 24 hours.
After storage for a period of time, the color density was measured using a reflective color thermometer manufactured by MacBeth. On the other hand, the same pressure-sensitive copying paper was colored in the same way in an environment of -5℃, the change in density immediately after coloring was measured using the same reflection colorimeter, and the results were stored at room temperature for 24 hours.
The relative color development rate at each elapsed time was determined when it was set as 100. The results are shown in Table-7. From Table-7,
This pressure-sensitive recording paper shows sufficient color development performance even at an initial time of 30 seconds. Table 7 Elapsed time 30 seconds 1 minute 1 hour Color development rate 70% 77% 88% Example 7 Pressure-sensitive recording by the method of Example 6 using the solvents obtained in Examples 2 to 4 and Comparative Example 1 A paper was prepared. The initial color development performance (development performance after 30 seconds of recording at -5°C) of the pressure-sensitive recording paper obtained is as follows. Table 8 Example 2 Example 3 Example 4 Comparative Example 1 Color development rate 57 62 72 25 (%) Test Example 1 Randomly selected man for the solvents obtained in Examples 1 to 4 and Comparative Examples 2 to 3・A panel test regarding odor was conducted by 20 women each.

[Table] A practically usable dye solvent for pressure-sensitive recording paper must have a rating of B or higher. Test Example 2 The solvents obtained in Examples 1 to 4 and Comparative Examples 2 to 3 were kept in constant temperature baths at 5°C and 0°C for 24 hours, and the presence or absence of crystal precipitation was examined. The results are shown in Table-10.

[Table] A practically usable dye solvent for pressure-sensitive recording paper must be rated B or higher. Example 8 500 g of biphenyl was charged into a glass autoclave with a capacity of 1, and the temperature inside the reactor was raised to 80° C. to melt it. Next, after adding 14 g of anhydrous aluminum chloride as a catalyst, the autoclave was sealed and stirring was started. Introduce propylene from the cylinder, raise the temperature inside the reactor to 100-110℃, and increase the pressure to about 1
Kg/cm ² ·G was maintained, and the reaction was continued until the average degree of alkylation was approximately 1. After the reaction was completed, the reaction product was washed with hydrochloric acid and water to remove the catalyst. The reaction solution obtained in this way was distilled in a vacuum precision distillation column,
Approximately 120 g of p-MIPB with a purity of 92% was separated, then cooled to 12°C with stirring in a glass container with a jacket, and the resulting slurry was centrifuged to separate p-MIPB with a purity of 99%. . On the other hand, 8% by weight of p-MIPB was obtained from the reaction product by distillation.
26g of 92% by weight DIPB mixture was separated, mixed with 99% pure p-MIPB obtained by crystallization, and p-
A mixed solution containing 73.2% by weight of MIPB and 26.8% by weight of DIPB was obtained. Pressure-sensitive paper using this mixed solution was prepared in Examples 5-
It was prepared by the method shown in Example 6, and the performance was compared by the method shown in Example 7. Result: Color density 59% at -5°C/30 seconds Odor B Crystal precipitation 5°C A 0°C A

[Brief explanation of drawings]

FIG. 1 is a triangular diagram showing the content ratios of m-MIPB, p-MIPB and DIPB.

Claims (1)

[Claims] 1 40 to 75% by weight of p-isopropylbiphenyl,
5-40% by weight of diisopropylbiphenyl and m-
A dye solvent for pressure-sensitive recording paper consisting of 20% by weight or less of isopropyl biphenyl. 2. A dye solvent for pressure-sensitive recording paper comprising 60 to 75% by weight of p-isopropylbiphenyl and 25 to 40% by weight of diisopropylbiphenyl.