JP3053229B2 - Manufacturing method of thermal recording sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a heat-sensitive recording sheet having excellent water resistance, solvent resistance and coloring.

[0002]

2. Description of the Related Art Conventionally, heat-sensitive recording sheets have been widely used for facsimile machines, computer terminals, measurement printers, medical measurement printers, and other recording sheets, or POS barcode labels. As a method for producing a heat-sensitive recording sheet, it is known that a colorless or pale-colored lactone compound such as crystal violet lactone and an acidic compound such as a phenol compound are coated on a support together with a water-soluble binder. . As the water-soluble binder, polyvinyl alcohol (hereinafter abbreviated as PVA), methylcellulose, carboxymethylcellulose, polyacrylic acid, styrene-maleic acid copolymer or starch is used,
Among them, PVA is widely used because of its excellent adhesive performance. However, the heat-sensitive recording sheet manufactured using the conventional water-soluble binder, the color image formed by the compatibility and reaction of the color-forming lactone compound and the acidic compound is unstable to moisture or an organic solvent, Due to contact with water or contact with a plasticizer or the like in PVC synthetic leather, there is a disadvantage that the color-developed portion is easily discolored or disappears. As a method for overcoming such drawbacks, as disclosed in JP-B-58-33117, JP-B-58-33119, JP-B-58-33839, and JP-B-59-30555, formalin, glyoxal and dialdehyde starch are disclosed. , Gurutarua Le dehydrogenase, aldehyde polyacrylamide, it is known that in combination with water-soluble binder, a water resistant agent, such as tetraborate alkali metal salts. As another method, as shown in JP-A-58-191194 and JP-A-58-193189, an attempt to improve water resistance by making PVA itself crosslinkable has been proposed. I have. However, in order to react PVA and dialdehyde to make PVA sufficiently water resistant, it is necessary to perform heat treatment at a high temperature of 100 ° C. or more. However, when the temperature is increased to 100 ° C. or more, the color developing lactone compound and the acidic compound Since coloration occurs due to compatibility and reaction, it is impossible to employ a heat treatment at such a high temperature. Therefore, in practice, heat treatment must be performed at a low temperature, and as a result, there is a problem that only insufficient water resistance can be obtained. On the other hand, crosslinkable PVA
Although the method of using a varnish does not necessarily require heat treatment at a high temperature, the fact is that it does not always satisfy the rigorous performance requirements for water resistance and solvent resistance required for recent POS labels and the like. In addition, JP-A-61-211081 describes
Does not require the special condition of high-temperature heat treatment.
To obtain a heat-sensitive recording sheet with excellent water resistance and solvent resistance.
For this purpose, a primary amino group or ammonium base
From PVA and water-proofing agents such as aldehyde compounds
Or a small amount of unmodified PVA
Are shown to match. However, such a
In the composition, it is apparent from Comparative Examples 2 and 3 described below.
As described above, although water resistance and solvent resistance are excellent,
The disadvantage of poor stability and often thickening over time
There is.

[0003]

SUMMARY OF THE INVENTION The present invention relates to the above prior art.
The purpose of this method is to eliminate the disadvantages of surgery.
Even without special treatment conditions, water resistance and
Excellent solvent resistance and excellent color development with less coloring problem
Excellent coating solution viscosity stability in the manufacturing process
Also has very well-balanced performance with little thickening
To provide a method for manufacturing a thermosensitive recording sheet
Things.

[0004]

Means for Solving the Problems The above object has been achieved in one molecule.
Polyvinyl having primary amino group or primary ammonium base
Nyl alcohol (A), polyvinyl alcohol (B) and
And water-resistant agent (C), and the mixing ratio of each component is
(B) 1 to 200 parts by weight of component (A) based on 100 parts by weight
Parts and 1 to 50 parts by weight of component (C).
Containing a thermosensitive coloring component and applying it to a support substrate,
Alternatively, the composition is applied to a support substrate having a thermosensitive coloring component layer.
By providing a method of manufacturing a thermal recording sheet to be applied.
Is achieved.

Hereinafter, the present invention will be described in more detail. The PVA (A) having a primary amino group or a primary ammonium group in the molecule used in the present invention includes a copolymer with a monomer having the functional group, or a saponification reaction and a hydrolysis reaction after copolymerization. And PVA obtained by copolymerizing a monomer that generates a primary amino group or a primary ammonium group, or a graft polymer or a block polymer containing PVA as one component. The average degree of polymerization of PVA (A) is usually 100 to 50.
00, preferably 200 to 2500, and the average degree of saponification is preferably 70 to 100 mol%. If the average degree of polymerization is less than 100, the performance as a binder, particularly the adhesive strength, is insufficient. On the other hand, if the average degree of saponification is less than 70 mol%, it is not preferable because it becomes difficult to dissolve in water. As a method for producing PVA (A) having a primary amino group or a primary ammonium group in the molecule, any method can be used, but an olefinically unsaturated monomer having a primary amino group or a primary ammonium group or a hydrolysis method The method (a) in which an olefinically unsaturated monomer having a substituent capable of forming a primary amino group or a primary ammonium group is copolymerized with a vinyl ester, followed by saponification or hydrolysis, is preferred. Other methods include a method (b) in which an aldehyde having a primary amino group or a primary ammonium group is introduced into PVA by an acetalization reaction, and a method (c) utilizing a Hoffman rearrangement reaction of an amino group.

Specific examples of the above-mentioned olefinically unsaturated monomer having a primary amino group or a substituent capable of forming a primary ammonium base by hydrolysis include vinylamine represented by the following formula 1, Examples thereof include acid salts and inorganic acid salts, N-vinylamide represented by Chemical Formula 2, and N-vinylimide represented by Chemical Formula 3.

[0007]

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[0008]

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[0009]

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(Wherein R 1 is a hydrogen atom or a methyl group, R 2 is a hydrogen atom or a lower alkyl group,
n shows 0-4 and m shows 2-4, respectively. )

As a catalyst for hydrolyzing the above copolymer, an acid or an alkali can be used. When an acid catalyst is used, the primary amino group generated by the hydrolysis of the amide group in the monomer unit represented by the above chemical formula 2 or 3 can be converted into a primary ammonium salt by subsequently reacting with the acid catalyst. it can. When an alkali catalyst is used, a primary amino group can be generated by hydrolysis of the amide group, and these can be reacted with an acid to form a primary ammonium salt. Examples of the aldehyde having a primary amino group or a primary ammonium group in the molecule used in the above method (b) include, for example, aminoacetaldehyde, aminobutyraldehyde, dialkylacetals thereof, and ammonium salts thereof. However, the present invention is not limited to this. The content of the primary amino group or primary ammonium base in the above-mentioned PVA (A) is 0.1%.
It is preferably at least 05 mol%, more preferably from 0.1 to 30 mol%. When the content of the primary amino group or the primary ammonium base is less than 0.05 mol%, the effect of the present invention is small, and when it exceeds 30 mol%, the expected effect is small for the content. .

As the PVA (B) used in the present invention, a water-soluble PVA is used. As the PVA (B), unmodified ordinary PVA is preferably used. PVA modified with a functional group other than a primary amino group or a primary ammonium base can also be used within a range that does not disturb the gist of the present invention. For example, carboxyl group-modified PVA, sulfonic acid group-modified PVA, phosphate group-modified PVA
Also used are anion-modified PVA such as A, cation-modified PVA modified with a compound other than primary amino group or primary ammonium group, or modified PVA copolymerized with ethylene, vinyl ether having long-chain alkyl, (meth) acrylamide, α-olefin, etc. it can. The degree of polymerization of PVA (B) is not particularly limited, but is usually selected from the range of 100 to 5000, preferably 200 to 2500.
The saponification degree of PVA (B) is not particularly limited as long as it is within a water-soluble range, but is usually selected from 70 to 100 mol%. The saponification degree of PVA (B) is preferably 85 to 1 in order to further increase the water resistance and the solvent resistance.
The content is preferably 00 mol%, more preferably 95 to 100 mol%.

The water-proofing agent (C) used in the present invention may be any compound capable of reacting with and cross-linking with a primary amino group or a primary ammonium base. Examples thereof include monoaldehyde compounds such as formaldehyde and acetaldehyde. Glyoxal, glutaraldehyde, polyaldehyde compounds such as dialdehyde starch, methylol melamine, methylol compounds such as dimethylol urea, aldehyde compounds such as a reaction product of ammonia and formaldehyde such as hexamethylenetetramine,
Alternatively, a water-soluble salt of a metal such as aluminum, iron, copper, zinc, titanium, magnesium, chromium, and zirconium may be mentioned. Of these, an aldehyde compound is preferably used.

The mixing ratio of PVA (A), PVA (B) and water-proofing agent (C) having a primary amino group or a primary ammonium group in the molecule is expressed in terms of weight ratio of component (B) 1.
It is necessary to use 1 to 200 parts of component (A) and 1 to 50 parts of component (C) based on 00 parts, and preferably 5 to 100 parts of component (A) based on 100 parts of component (B). Component (C) is 1 to 20 parts. When the amount of the component (A) is less than 1 part, effects such as water resistance and solvent resistance are not exhibited,
When the amount exceeds 200 parts, the viscosity stability of the coating liquid is poor, the viscosity increases over time, or when used as a binder for a heat-sensitive recording sheet, the moisture absorption is unnecessarily large in a high-humidity atmosphere, and It leads to a decrease in water resistance and further coloring,
Not preferred. If the amount of the component (C) is less than 1 part, there is no effect as a water-proofing agent. The present invention can exhibit excellent effects when the mixing ratio of the above three components is used, and when the ratio is outside the above range, the sheet properties such as water resistance, solvent resistance, and color developing performance of the heat-sensitive recording sheet are impaired. In addition, problems often arise in the viscosity and viscosity stability of the coating solution in the manufacturing process, and a balanced effect cannot be obtained.

The composition comprising PVA (A) having a primary amino group or a primary ammonium group in the molecule and a waterproofing agent (C) has excellent sheet properties such as water resistance and solvent resistance. Despite its properties, there is a problem with the viscosity stability of the coating solution, and the viscosity often increases with time. The sheet properties are also high temperature and high humidity, for example, 40 ° C., 90% RH.
If left in an atmosphere for a long period of time, it absorbs moisture more than necessary as described above, easily causing a decrease in water resistance and causing curling, and causes problems such as coloring yellow. This PVA
By combining PVA (B) with (A) and the waterproofing agent (C) at the above-mentioned mixing ratio, a balanced and excellent effect is exhibited.

As the thermosensitive coloring component in the thermosensitive recording sheet of the present invention, two components of a coloring material and a developing material which reacts with the coloring material upon heating to form a color can be exemplified. A typical example of the color-forming substance among the thermosensitive color-forming components is a color-forming lactone compound.
The color-forming lactone compound may be any compound capable of forming a color by reacting with an acidic compound when heated, and includes, for example, various types such as triphenylmethane, triphenylmethanephthalide, fluoran, leuco auramine, and spiropyran. Leuco compounds. In general, the color developing substance among the heat-sensitive coloring components may be any acidic compound having a property of liquefying or vaporizing at 70 ° C. or higher and reacting with the leuco compound to form a color. -Hydroxyacetophenone, 2,2'-diacetoxyphenyl, 2,2'-methylenebis (4-chlorophenol), 2,2'-methylenebis (4-methyl-6-t-butylphenol), 4,4'-isopropyl Ridendiphenol, 4,4'-isopropylidenebis (2-chlorophenol), 4,4'-isopropylidenebis (2-methylphenol), 4,4'-sec-
Butylidenephenol, 4,4'-ethylenediphenol, 4,4'-ethylenebis (2-methylphenol)
And the like. Examples of the support substrate used in the heat-sensitive recording sheet of the present invention include paper such as high-quality paper, medium-quality paper, and coated paper, or plastic films, film-laminated paper, and woven fabric sheets.

The method for producing the heat-sensitive recording sheet of the present invention will be described below by taking as an example the case where a color-forming lactone compound and a phenol compound are used. The color-forming lactone compound and the phenol compound are separately pulverized into fine particles by pulverization, and if necessary, various clays, talc, fillers such as calcium carbonate, waxes, melting point regulators, surfactants, and the like are added. A composition comprising PVA (A) having a primary amino group or a primary ammonium group in the molecule, PVA (B) and a waterproofing agent (C) is added to form a heat-sensitive coating solution, which is coated on a supporting substrate and dried. To form a thermosensitive coloring component layer. In some cases, a layer of a composition comprising PVA (A), PVA (B) and a waterproofing agent (C) having a primary amino group or a primary ammonium group in the molecule is formed on the thermosensitive coloring component layer. At this time, PVA (A) or PVA having a primary amino group or a primary ammonium group in the above-mentioned molecule in advance on the supporting substrate.
It is also effective to apply the above-mentioned heat-sensitive coating liquid after forming a heat-sensitive coloring component layer having a composition comprising (B) and a water-proofing agent (C). Further, as a top coat layer of a heat-sensitive recording sheet manufactured without using the composition of the present invention,
A layer composed of the three-component composition of the present invention containing no thermosensitive coloring component can be formed on the thermosensitive coloring component layer. In addition, it is inevitable to mix a conventionally known water-soluble resin such as carboxymethylcellulose or starch in a small proportion with the composition comprising PVA (A), PVA (B) and water-proofing agent (C). PVA (A) described above,
When PVA (B) and the water-proofing agent (C) are used as binders in the heat-sensitive coloring component layer, the amount is preferably 1 to 500 parts per 100 parts of the heat-sensitive coloring component. 200 parts is more preferred. When a layer comprising the composition of the present invention is formed on the thermosensitive coloring component layer, the coating amount as a solid content is preferably 0.5 to 5 g / m2. Further, the above PVA component (A), PVA
The concentration of the aqueous coating solution of the composition comprising (B) and the waterproofing agent (C) is preferably from 0.5 to 20% by weight, more preferably from 2 to 10% by weight.

[0018]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. In Examples, “%” and “parts” are based on weight unless otherwise specified. The evaluation of the performance of the thermal paper and the evaluation of the physical properties of the coating liquid were performed as follows. [Evaluation of Water Resistance] After immersing the prepared heat-sensitive recording sheet in water at 20 ° C. or 40 ° C. for 24 hours, the degree of elution by rubbing the coated surface with a finger was evaluated in five steps. [Evaluation of Solvent Resistance] The prepared heat-sensitive recording sheet was heated and colored, and the coloring density was measured with a Macbeth densitometer.
After standing in a thermostat for 2 days, the coloring density was measured to compare and evaluate the discoloration by the plasticizer. [Evaluation of Colorability] The prepared heat-sensitive recording sheet was left in a constant temperature and humidity chamber at 40 ° C. and 90% RH for 7 days to check the colorability before and after the storage.
The Δb of the coated surface was measured and evaluated using a color difference meter. [Viscosity Change of Coating Liquid] After measuring the viscosity of the prepared coating liquid at 30 ° C. with a BL viscometer, measuring the viscosity after standing in a constant temperature bath at 30 ° C. for 24 hours, the viscosity ratio before and after standing (Based on the viscosity immediately after the adjustment) was calculated.

EXAMPLE 1 A copolymer of N-vinylacetamide and vinyl acetate was alkali-saponified to contain 5 mol% of primary amino groups, to have a saponification degree of vinyl acetate units of 98.5 mol% and a polymerization degree of 1150. PVA having a primary amino group in the molecule
(A) was obtained. 40 parts of this PVA (A) and a degree of polymerization of 12
40, unmodified PVA (B) 6 having a saponification degree of 98.5 mol%
0 parts were dissolved in water containing lactic acid in an equimolar amount to the primary amino group of the amino group-modified PVA (A), and the concentration was 15%.
Of PVA (A) and PVA (B). This is designated as solution A. Next, 8 parts of crystal violet lactone, 25 parts of kaolin clay, 15 parts of stearic acid amide, a small amount of a dispersant and water were added to give a concentration of 3 parts.
The solution prepared as a 0% solution is referred to as solution B. Further, 25 parts of bisphenol A, 25 parts of kaolin clay, a small amount of a dispersant and water are added to prepare a 30% solution, which is referred to as liquid C. The B liquid and the C liquid are separately placed in a paint shaker, and are crushed and dispersed using 2 mmφ glass beads.
30 parts of liquid B and 30 parts of liquid C were mixed. To the solution was added 30 parts of solution A, and then a 40% aqueous glyoxal aqueous solution was added in an amount of 10% based on the total amount of PVA (A) and PVA (B) on a pure matter basis to prepare a heat-sensitive coating solution. did.
The heat-sensitive coating liquid was coated by a wire bar so that the coating liquid after drying on a high-quality paper 50 g / m ² becomes 7g / m ^2, 50
After drying at 50 ° C, 50 ° C, 50 kg / cm ² , 10m /
The sheet was passed through a calender roll three times under the conditions of min to obtain a thermosensitive recording sheet. The performance of this heat-sensitive recording sheet was evaluated, and the results are shown in Table 1.

Example 2 N-vinylacetamide used in Example 1 was replaced by N
-PVA (A) modified with primary amino group by copolymerization with vinyl acetate using vinyl succinimide and alkali saponification
It was created. This PVA (A) contains 7 mol% of primary amino groups, has a saponification degree of vinyl acetate units of 99.2 mol%,
The polymerization degree was 1,050. PVA used in Example 1
In the same manner as in Example 1 except that the above PVA (A) was used instead of (A) and glutaraldehyde was used instead of glyoxal, a heat-sensitive recording sheet was prepared and its performance was evaluated. The results are shown in Table 1.

EXAMPLE 3 12 mol% of a primary ammonium base obtained by acetalizing PVA having a saponification degree of 99.3 mol% and a polymerization degree of 820 with aminoacetaldehyde in an aqueous hydrochloric acid solution.
The PVA (A) contained in the PVA was used in Example 1.
Except that it was used instead of (A), the same as in Example 1
A heat-sensitive recording sheet was prepared and its performance was evaluated. The results are shown in Table 1.

Example 4 By copolymerizing acrylamide and vinyl acetate,
A modified polyvinyl acetate containing 14 mol% of acrylamide was synthesized. Subsequently, the modified PVA obtained by saponification is subjected to a Huffman rearrangement reaction to obtain a PVA having a primary amino group.
(A) was obtained. The degree of saponification of vinyl acetate units was 98.6 mol%, the degree of polymerization was 1750, and the content of primary amino groups was 9 mol%. PVA using this PVA (A) in Example 1
A heat-sensitive recording sheet was prepared and evaluated in the same manner as in Example 1 except that glycol acid was used instead of lactic acid instead of (A). The results are shown in Table 1.

Example 5 PVA containing a primary amino group in solution A of Example 1
40 parts to 6 of the mixing ratio of (A) and unmodified PVA (B)
Instead of 0 parts, the mixing ratio is 26 parts to 75 parts, and PVA (A) and PVA (B) dissolved in water and having a concentration of 15% are used.
Was prepared. A heat-sensitive recording sheet was prepared in the same manner as in Example 1 except that this was used as the solution A, and its performance was evaluated. The results are shown in Table 1.

COMPARATIVE EXAMPLE 1 Instead of the solution A of Example 1, a non-modified PVA (B) having a saponification degree of 98.5 mol% and a polymerization degree of 1240 having a concentration of 15% was used.
A heat-sensitive recording sheet was prepared and its performance was evaluated in the same manner as in Example 1 except that the aqueous solution A (B) was used as the liquid A. The results are shown in Table 1.

Comparative Example 2 The procedure of Example 1 was repeated except that the aqueous solution of PVA (A) having a concentration of 15% of the primary amino group-containing PVA (A) used in Example 1 was used instead of the solution A of Example 1. In the same manner as in Example 1, a heat-sensitive recording sheet was prepared and its performance was evaluated. The results are shown in Table 1.

Comparative Example 3 PVA Containing Primary Amino Group in Solution A of Example 1
40 parts to 6 of the mixing ratio of (A) and unmodified PVA (B)
The heat sensitivity was the same as in Example 1 except that the mixing ratio was 80 parts to 20 parts with respect to 0 parts, and an aqueous solution consisting of PVA (A) and PVA (B) having a concentration of 15% was used as the solution A. A recording sheet was prepared and its performance was evaluated. The results are shown in Table 1.

[0027]

[Table 1]

Example 6 The solution A of Example 1 was diluted to 10%, and glyoxal was added so as to be 5% of the total amount of PVA (A) and PVA (B) in terms of pure components. A working solution was prepared. This coating solution is coated on the surface of a commercially available thermal paper for printing at a solid content of 3 g.
/ M ² , dried at 50 ° C., and calendered. When the performance of this thermal paper was evaluated, the water resistance was 5 at both 20 ° C. and 40 ° C.
In addition, the discoloration of the solvent was very low. In addition, the viscosity increase of this clear coat liquid was as small as 1.13, which was favorable. Even when the obtained heat-sensitive recording sheet was allowed to stand in a high-temperature and high-humidity atmosphere (40 ° C., 90% RH) for 7 days, no yellowing or curling was observed.

Example 7 Acrylamide was polymerized in the presence of a modified PVA having a thiol group at a molecular terminal, and a molar ratio of PVA-85: 15 was obtained.
An acrylamide block copolymer was obtained. The copolymer was subjected to Hoffman rearrangement to obtain a block copolymer PVA (A) containing 4 mol% of primary amino groups. 40 parts of the above block copolymer PVA (A) and the unmodified PV used in Example 1
Using 60 parts of A (B), an aqueous solution composed of PVA (A) and PVA (B) having a concentration of 10% was obtained. An overcoated thermosensitive recording paper was obtained in the same manner as in Example 6 except that hexamethylenetetramine was used instead of the PVA solution and glyoxal of Example 6. When this performance evaluation was performed, the water resistance performance was 5 at both 20 ° C. and 40 ° C. In addition, the discoloration of the solvent was very low. The viscosity increase of the clear coat liquid was also 1.08.
It was small and good. Even when the obtained heat-sensitive recording sheet was allowed to stand in a high-temperature and high-humidity atmosphere (40 ° C., 90% RH) for 7 days, no yellowing or curling was observed.

[0030]

The method for producing the heat-sensitive recording sheet of the present invention comprises:
Since the viscosity rise of the coating liquid of the composition to be used is small, the workability is extremely good, and the obtained heat-sensitive recording sheet does not require severe heat treatment, and is extremely excellent in water resistance and solvent resistance. Further, there is no defect such as coloring or curling even when left for a long time under high temperature and high humidity.

Continued on the front page (72) Inventor Hitoshi Maruyama 1621 Sazu, Kurashiki-shi, Okayama Prefecture Kuraray Co., Ltd. Examiner Isao Fujii (56) References JP-A-61-211081 (JP, A) JP-A-61-123586 ( JP, A) JP-A-61-209191 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5/28-5/34

Claims (2)

(57) [Claims] 1. A primary amino group or a primary ammonium group in a molecule.
Polyvinyl alcohol (A) having an aluminum base, polyvinyl alcohol
Nyl alcohol (B) and a waterproofing agent (C),
The mixing ratio of each component is 100 parts by weight of component (B).
(A) 1 to 200 parts by weight and component (C) 1 to 50 parts by weight
Parts by weight of a composition which contains a thermosensitive coloring component
Apply to a supporting substrate or apply the composition to
Heat sensitivity characterized by being applied to a support substrate having a layer
Manufacturing method of recording sheet. 2. A water-proofing agent (C) is the preparation of heat-sensitive recording sheet according to claim 1 is an aldehyde compound.