JPS6216197B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat-sensitive recording material, and more specifically, the present invention relates to a water-resistant coating film of a heat-sensitive recording material containing a phenolic compound, a white or light coloring substance that develops color by reacting with the phenolic compound under heat, and a water-soluble binder. It is about sexual improvement. Thermosensitive recording materials using color-forming substances such as triphenylmethane, fluoran, or phenothiazine and phenolic compounds are well known.
In general, a heat-sensitive recording material using a two-component coloring agent as described above is produced by finely dispersing the coloring substance and the phenolic compound separately in an aqueous binder solution using a ball mill, etc., and then mixing the respective dispersions and dispersing them as necessary. Depending on the requirements, dispersants, antifoaming agents, lubricants such as wax, white pigments, sensitivity regulators, etc. are added to create a coating solution, which is then applied to a support and dried. When the heat-sensitive recording material prepared as described above is stored or used in a humid state or water is spilled on it, the coating film becomes sticky or starts to run, so it is necessary to make the coating film waterproof. Conventionally, glyoxal, melamine/formaldehyde resin, and the like have been used as waterproofing agents for the coating film. However, glyoxal has little water resistance effect and may cause yellowing of heat-sensitive recording materials, and melamine formaldehyde resin releases toxic formalin, and furthermore, it requires high temperatures (over 100℃) to obtain sufficient water resistance effect. There are disadvantages such as the need for drying or heat treatment. Drying or heat treatment at high temperatures causes color development on the background of the heat-sensitive recording material, and therefore cannot be carried out in the production of heat-sensitive recording materials. The present inventors have conducted extensive research to improve the above-mentioned drawbacks of heat-sensitive recording materials, and as a result, we have developed a thermosensitive recording material by using the following water-soluble polyvinylamide derivative (hereinafter abbreviated as PAL) as a water-resistant agent. The inventors have now completed the present invention by discovering that the water resistance of the coating film can be significantly improved without impairing its properties. PAL has structural units represented by the following general formulas A, B, C, and D in the order of ABCD in a molar ratio P:q:r:s
(p, q, r, s are q/(p+q)=0.1~1.0,
r/(p+q+r+s)=0.001~0.1, s/r=
It is a polyvinylamide derivative with a degree of polymerization of about 100 to 1000, which is arranged in a linear manner in numbers such as 0 to 5. (In the formula, R ₁ , R ₂ and R ₆ are H or CH ₃ :R ₃ , R ₄
is an alkyl group having 1 to 3 carbon atoms; Z is an alkyl group having 2 to 6 carbon atoms
alkylene group; M is H, alkali metal or ammonium salt; R ₅ is H or COOM; X is C1, Br or I; Y is an anion) Alternatively, it is produced by copolymerizing with a vinylamide monomer and an anionic monomer to form a polyvinylamide copolymer, and then adding glyoxal to the copolymer. (In the formula, R ₂ is H or CH ₃ ; R ₃ and R ₄ are an alkyl group having 1 to 3 carbon atoms; Z is an alkylene group having 2 to 6 carbon atoms; X is C1, Br, or I; Y is an anion) Among the four structural units of PAL, the general formula A
Water-soluble vinylamides such as acrylamide and methacrylamide are preferred. The structural unit represented by general formula B is obtained by adding glyoxal to part or all of the amide group of general formula A, and the amount of glyoxal added is in a molar ratio of q/(p+q)=0.1 to 1.0. It is preferably 0.2 to 0.5, and more preferably 0.2 to 0.5. If the amount added is less than the lower limit of the above range, sufficient water resistance effect will not be exhibited. The structural unit represented by the general formula C is obtained by neutralizing an aminoalkyl ester of acrylic acid or an aminoalkyl ester of methacrylic acid with a mineral acid such as nitric acid, hydrochloric acid or phosphoric acid, and then producing a structural unit such as epichlorohydrin, epibromohydrin or epichlorohydrin. It is a cationic monomer obtained by adding epihalohydrin such as iodohydrin. Examples of aminoalkyl esters of acrylic acid or methacrylic acid include 2-dimethylaminoethyl acrylate, 2-diethylaminoethyl acrylate, 3-dimethylaminopropyl acrylate, 2-dimethylaminoisopropyl acrylate, and methacrylates corresponding to these esters. Examples include aminoalkyl esters of acids. The copolymerization ratio of the structural units represented by general formula C is molar ratio r/(p+q+r+s)=0.001~
It is preferably 0.1, and more preferably 0.01 to 0.05. Even if the copolymerization ratio of the structural units is above the upper limit of the above range, the water resistance effect is not much different from that when it is within the above range, and it is not economically advisable to use an unnecessarily large amount of the expensive cationic monomer (1 formula). . On the other hand, below the lower limit, the water resistance effect will not be sufficiently exhibited.
Structural units represented by general formula D include monobasic unsaturated carboxylic acids such as acrylic acid and natacrylic acid, dibasic unsaturated carboxylic acids such as maleic acid and maleic anhydride, or monobasic unsaturated carboxylic acids such as maleic acid and maleic anhydride;
Water-soluble anionic monomers such as alkali metal salts such as Na and K and ammonium salts are preferred. The copolymerization ratio of the structural units is preferably a molar ratio of s/r=0 to 5, more preferably 0.5 to 2.0.
If the copolymerization ratio of the structural units exceeds the upper limit of the above range, the water resistance effect will not be sufficiently exhibited. The degree of polymerization of PAL is preferably about 100 to 1000 in order to improve the handling and storage stability of the PAL solution. If the degree of polymerization is less than about 100, a sufficient water resistance effect cannot be obtained, while if the degree of polymerization is more than about 1000, the viscosity of the PAL solution increases, resulting in poor handling and storage stability. Although PAL alone exhibits excellent performance as a water-soluble binder and significantly improves the water resistance of coatings, it is economically advantageous to use it as a water-resistant agent for inexpensive water-soluble binders such as oxidized starch and carboxymethyl cellulose. . The amount of PAL added is preferably 1% by weight or more in terms of solid content with respect to the water-soluble binder, and a sufficient water resistance effect is exhibited at 5 to 15% by weight. The colorless to light-colored color-forming substance used in the present invention is generally called a leuco compound and develops color by reacting with an acidic substance, such as spiropyran-based, fluoran-based, triphenylmethane-based,
Examples include various leuco bodies such as phenothiazine type and leuco auramine type. Furthermore, the phenolic compound used in the present invention is one that is solid at room temperature and liquefies or vaporizes at 70 to 200°C to react with the leuco compound to develop a color, including 4,4'-isopropylidene diphenol, 4
-tertiary butylphenol, 4,4'-secondary butylidene diphenol, 4-hydroxydiphenoxide, 4-hydroxyacetophenone, 2,2'-methylenebis(4-chlorophenol) and 4,4'-isopropylidene Examples include bis(2-methylphenol). Examples of water-soluble binders include modified starches such as oxidized starch, starch derivatives such as phosphate-modified starch, gelatin, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC),
Natural or synthetic water-soluble polymers such as hydroxypropylcellulose (HPC), methylcellulose (MC), gum arabic, sodium alginate, polyvinylpyrrolidone, polypinyl alcohol (PVA) and polyacrylamide can be mentioned. These water-soluble binders can be used alone or in combination of two or more. Furthermore, one or more of the above water-soluble binders and a latex such as SBR can also be used in combination. Note that as the support, any material such as paper, synthetic paper, or synthetic resin film can be used. The present invention will be explained in more detail with reference to Examples below. Note that the reference example shows an example of a method for synthesizing PAL used in the present invention. However, in the example, %
is weight %, and parts are parts by weight. Reference Example 1 Synthesis of PAL(1) 2-dimethylaminoethyl methacrylate 240g
After neutralizing a mixed solution of and 120g of water with 6N nitric acid,
Add 140g of epichlorohydrin to the solution,
The reaction was carried out at °C for 8 hours to obtain a cationic monomer solution having the following structural formula (), which was diluted with water to give a 25% solution. A mixed solution of 200 g of water and 40 g of isopropanol was then heated to reflux and 192 g of acrylamide was added separately but simultaneously to the solution over a period of about 1 hour.
and 34 g of the above 25% cationic monomer to 230 g of water.
A solution of 1 g of ammonium persulfate dissolved in 100 g of water was added. After the addition, the reaction was continued under reflux for about 1 hour to obtain a 25% cationic polyacrylamide copolymer with a degree of polymerization of about 500, in which structural units represented by the following formulas A and C were linearly arranged in a molar ratio of 99.0:1.0. A combined solution was obtained. Gardner viscosity was EF. Next, PH 200g of the 25% copolymer solution with 1N NaOH.
9.5, then 39 g of 20% glyoxal, which had been previously adjusted to PH 7.0, was added and reacted at 60°C for 1 hour, so that the structural units represented by the above formulas A and C and the following formula B were 79.2 in ABC order: A 20% polyacrylamide derivative [hereinafter abbreviated as PAL (1)] having a degree of polymerization of about 500 and linearly arranged at a molar ratio of 19.8:1.0 was obtained. Gardner viscosity was A. Reference Example 2 Synthesis of PAL(2) A mixed solution of 200 g of water and 40 g of isopropanol was heated to reflux, and 190 g of acrylamide and 34 g of the 25% cationic monomer of Reference Example 1 were added to the solution separately but simultaneously over about 1 hour. A solution of 2 g of 98% acrylic acid dissolved in 230 g of water and a solution of 1 g of ammonium persulfate dissolved in 100 g of water were added. Below, in the same manner as Reference Example 1, Reference Example 1
A 20% polyacrylamide derivative with a degree of polymerization of about 600 [hereinafter referred to as PAL ( 2)] was obtained. Gardner viscosity was A-B. Reference Example 3 Synthesis of PAL (3) Synthesis of PAL (3) The same procedure as Reference Example 2 was carried out except that 3 g of maleic acid was used instead of 2 g of 98% acrylic acid. A 20% polyacrylamide derivative (hereinafter abbreviated as PAL(3)) with a degree of polymerization of approximately 500 was obtained in which the structural units were linearly arranged in the order of ABCE at a molar ratio of 78.4:19.6:1.0:1.0. Gardner viscosity was A. Examples 1 to 6 (1) Preparation of paint

[Table] Put both liquids A and B above into separate ball mills.
After pulverization and mixing for 24 hours, both solutions were mixed. to the mixture
PAL (1), commercially available melamine formaldehyde resin (MF resin), or glyoxal were added to the composition shown in Table 1, and diluted with water to obtain a paint with a solid content concentration of 20%. (2) Application to paper The paint from (1) was applied to commercially available high-quality paper (basis weight 54 g/m ² , LBKP) using a coating rod to a coating amount of 7 g/m ² and dried at 70°C for 3 minutes. did. (3) Water resistance test (i) Finger evaluation (ring finger method) One drop of water is placed on the coated surface of the heat-sensitive recording material, and after 15 seconds, the fingertip of the ring finger is rubbed strongly 5 times at a distance of 3 cm to evaluate the coating film. I observed the condition. Water resistance 1 (poor) to 5 (excellent)
It was evaluated on a five-point scale. (ii) Evaluation using a printing suitability tester (RI method) The coated surface of the heat-sensitive recording material was brought into contact with the wet roll of an RI tester (manufactured by Mei Seisakusho) for 5 seconds, and then printed with off-wheel ink with a tack value of 10. The condition of the coating film was observed. Water resistance was evaluated on a five-point scale from 1 (poor) to 5 (excellent). (4) Results are shown in Table 1.

[Table] Examples 7 to 11 The composition of the paint is as follows, and instead of PAL(1),
The same procedure as in Example 1 was carried out except that PAL(2) was used. However, the solid content concentration of the paint was 30%, and the coating amount was targeted at 8 g/m ² .

【table】

【table】 The results are shown in Table 2.

[Table] Examples 12 to 15 The composition of the paint is as follows, and instead of PAL(1),
The same procedure as in Example 1 was carried out except that PAL(3) was used.

【table】 The results are shown in Table 3.

[Table] As is clear from the examples above, when PAL is used, the water resistance of the coating film is significantly improved compared to when conventional water resistant agents such as glyoxal and melamine/formaldehyde resin are used.

Claims (1)

[Scope of Claims] 1. A heat-sensitive recording material containing a phenolic compound, a white or light-colored color-forming substance that develops color by reacting with the phenolic compound under heat, and a water-soluble binder, as a water-resistant agent for a coating film. The following general formula A,
The structural units represented by B, C and D have a molar ratio p:q:r:s (p, q, r, s are q/(p
+q)=0.1~1.0, r/(p+q+r+s)=0.001
A thermosensitive recording material characterized by using a polyvinylamide derivative having a degree of polymerization of about 100 to 1000 arranged in a linear manner with a polyvinylamide derivative having a polymerization degree of about 100 to 1000. (In the formula, R ₁ , R ₂ and R ₆ are H or CH ₃ :R ₃ , R ₄
is an alkyl group having 1 to 3 carbon atoms: Z is an alkyl group having 2 to 6 carbon atoms
alkylene group: M is H, alkali metal or ammonium salt: R ₅ is H or COOM: X is C1, Br or I: Y is an anion) 2 The polyvinylamide derivative has the following formula A',
It has structural units represented by B', C' and D', and the structural units have a molar ratio p:q:
r: s (p, q, r, s is q/(p+q)=0.1~
1.0, r/(p+q+r+s)=0.001~0.1, s/
2. The heat-sensitive recording material according to claim 1, which is a polyacrylamide derivative having a degree of polymerization of about 100 to 1000 and linearly arranged with r=0 to 5. (In the formula, Y is NO ₃ or C1: M is H, alkali metal or ammonium salt) 3 The polyvinylamide derivative has the following formula A'',
It has structural units represented by B″, C″ and D″, and the structural units have a molar ratio p:q: in the order of A″, B″, C″, D″.
r: s (p, q, r, s is q/(p+q)=0.1~
1.0, r/(p+q+r+s)=0.001~0.1, s/
2. The heat-sensitive recording material according to claim 1, which is a polyacrylamide derivative having a degree of polymerization of about 100 to 1000 and linearly arranged with r=0 to 5. (In the formula, Y is NO ₃ or C1: M is H, alkali metal or ammonium salt)