JPH0565636B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an aqueous solution of a polyvinyl alcohol graft copolymer and an agent for forming a protective layer on processed surfaces of paper containing the same, particularly for information recording on photographic paper, thermal recording paper, etc. This invention relates to a protective layer forming agent that can impart excellent oil resistance, plasticizer resistance, and water resistance to paper.

[Conventional technology] In recent years, with the development of information devices and labor-saving machines,
Various information recording papers have been developed and put into practical use. In particular, thermal recording paper is widely used in computer output, printers such as calculators, recorders of various automatic measuring instruments, facsimile machines, copying machines, automatic ticket vending machines, and other fields, and is in high demand. On the other hand, the performance requirements for these recording papers are becoming stricter year by year. For example, in the case of thermal recording papers, they not only have heat-sensitive properties such as states king and color development, but also oil,
There is a growing demand for performance that can be called oil-resistant and water-resistant, so that the colored parts do not disappear or bleed due to chemicals such as water and plasticizers. That is, the thermal recording paper contains a leuco dye-based coloring agent such as crystal violet, bisphenol A, etc.
A heat-sensitive coating liquid is obtained by dispersing a color developer such as , filler such as wax, etc. in water, and adding a binder made of an organic polymer substance to this liquid, and applying this to the surface of high-quality base paper to form a heat-sensitive layer. The heat-sensitive layer is manufactured by forming a color, and the heat-sensitive layer develops color when used by a heat head of a printing device or the like. Therefore, when the colored part of the recording paper is used in applications where it comes into contact with plasticizers or oil, it is known that there is a problem in that the plasticizer or oil reacts with the coloring agent and causes it to disappear. There is. It has also been pointed out that when used in applications that come into contact with water or aqueous liquids, the water permeates the heat-sensitive layer, dissolves the binder, and causes the colored portion to peel off.

In order to overcome these difficulties with thermal recording paper, conventional methods have been used to improve oil and water resistance and storage stability by reducing the amount of binder, wax, etc. used when formulating thermal coating liquids to an extent that does not impair color development. Attempts have been made to increase the heat-sensitive layer. However, with such a method, the improvement in oil resistance and water resistance is small and cannot be said to be practically sufficient.

[Problem that the invention seeks to solve]

Recently, attempts have been made to improve oil resistance and water resistance by forming a protective layer in the form of a three-dimensional network obtained by reacting a water-soluble polymer with a crosslinking agent. For example, JP-A-59-
1797 and 59-226026 disclose the use of a polymer obtained by graft polymerizing (meth)acrylamide and a vinyl monomer to polyvinyl alcohol. However, even with this protective layer forming agent, the oil resistance of the resulting processed paper (processed surface of paper)
Plasticizer resistance and water resistance are still not truly sufficient. Also, JP-A-58-181687, 59-
106995 and 59-123697 disclose that a resin layer is formed on the surface of processed paper using a polymer in which acetoacetyl groups are introduced into the main chain of polyvinyl alcohol or copolymer-modified polyvinyl alcohol. However, when using this polymer, there are drawbacks such as poor workability due to foaming during processing, and staking.

The object of the present invention is to have excellent performance in imparting oil resistance, plasticizer resistance, and water resistance to processed paper, particularly leuco dye-based thermal recording paper, and to provide excellent coating workability and performance of the processed paper itself. An object of the present invention is to provide a protective layer-forming agent for processed paper that does not impair the properties of processed paper, and an aqueous polyvinyl alcohol graft copolymer solution that can be used therein.

[Means for solving problems]

According to the present invention, (A) polyvinyl alcohol and/or copolymerized modified polyvinyl alcohol,
Graft copolymer with (B) acrylamide and/or methacrylamide, (C) at least one polymerizable monomer having a carboxyl group, and (D) at least one polymerizable monomer having an acetoacetyl group. An aqueous solution of is provided.

According to the present invention, at least one of (A) polyvinyl alcohol and/or copolymerized modified polyvinyl alcohol, (B) acrylamide and/or methacrylamide, (C) a polymerizable monomer having a carboxyl group, and (D) A protective layer forming agent for processed paper containing an aqueous solution of a graft copolymer with at least one polymerizable monomer having an acetoacetyl group is provided.

The polyvinyl alcohol and copolymer-modified polyvinyl alcohol used here may be water-soluble and generally well-known ones. As polyvinyl alcohol, it has a degree of polymerization of 200 to 2500,
It is preferably a completely saponified product or a partially saponified product with a degree of saponification of 75 to 100%. Examples of copolymerized modified polyvinyl alcohol include acrylic acid, methacrylic acid, itaconic acid, maleic acid,
Fumaric acid, allyl alcohol, allyl acetate, allyl propionate, allyl butyrate, allyl sulfonic acid, methallyl sulfonic acid, methyl vinyl ether, ethyl vinyl ether, vinyl methyl ketone, vinyl ethyl ketone, N-vinyl pyrrolidone, ethylene, propylene, isobutylene, Vinyl ester of higher fatty acid having 8 to 18 carbon atoms, N-alkylacrylamide whose alkyl group has 4 to 12 carbon atoms, diacetone acrylamide, general formula (), [Here, n is 0 to 4, m is 0 to 2, R ¹ is an alkyl group having 1 to 5 carbon atoms, R ² is an alkoxyl group or acyloxyl group having 1 to 40 carbon atoms (here, alkoxyl group and acyloxyl group are may have an oxygen-containing substituent). ] Vinylsilane represented by and general formula (), [Here, m is 0 to 2, R ¹ is an alkyl group having 1 to 5 carbon atoms, and R ² is an alkoxyl group or acyloxyl group having 1 to 40 carbon atoms (here, alkoxyl group and acyloxyl group are oxygen-containing substituents) ), R ³ is a hydrogen atom or a methyl group, R ⁴ is a hydrogen atom or an alkyl group having 1 to ⁵ carbon atoms, R is an alkylene group having 1 to 5 carbon atoms, or a chain carbon atom is oxygen or 2 interconnected by nitrogen
[indicates organic residues].

There is a copolymerized modified polyvinyl alcohol having a saponification degree of 75 to 100%, which is copolymerized with at least one polymerizable monomer represented by the formula, preferably in an amount of 1 to 20% by weight.

In the present invention, the amount of component (A) forming the graft copolymer is preferably 10 to 60% by weight, and the amount of component (B), component (C) and component (D) is preferably 20 to 70% by weight.
% by weight, preferably 3-10% by weight and 10-30% by weight.

The polymerizable monomer having a carboxyl group as component (C) is a compound having one ethylenically unsaturated double bond and one or two carboxyl groups, and preferable examples include acrylic acid,
Methacrylic acid, itaconic acid, maleic acid, etc.
There is fumaric acid.

The polymerizable monomer having an acetoacetyl group is a compound having one or more acetoacetyl groups (CH ₃ COCH ₂ CO-) and one ethylenically unsaturated double bond. Examples of such compounds include allyl acetoacetate, isobutenyl acetoacetate, acrylic acid or methacrylic acid 2-acetoacetyloxypropyl ester, general formula (), [Here, R is a hydrogen atom or a methyl group, and n is 1 to
Indicates an integer of 4. ] Acetoacetic ester and acetoacetylethylene, There is.

The above-described protective layer forming agent for processed paper containing the aqueous solution of the graft copolymer of the present invention is used together with at least one crosslinking agent having a functional group that reacts with an acetoacetyl group during paper processing. As the crosslinking agent having a functional group that reacts with an acetoacetyl group, for example, a conventionally known crosslinking agent having an aldehyde group or a methylol group can be used,
Specific examples include polyhydric aldehydes such as glyoxal, glutaraldehyde, dialdehyde starch, urea-formalin initial condensates such as dimethylol urea, and melamines such as trimethylol melamine.
Examples include formalin initial condensates and acetone-formalin initial condensates such as dimethylolacetone.

Since the acetoacetyl group in the graft copolymer has an active methylene group, it reacts with functional groups such as aldehyde groups and methylol groups to form stable bonds. Therefore, when such a crosslinking agent is used, a strong film can be formed within a short time even at room temperature.

The present inventors believe that as a protective layer-forming agent for processed paper, the inherent properties of processed paper, especially in heat-sensitive recording paper, such as no fogging, no staining, and high color development heat sensitivity, etc. In order to achieve the initial objective, the properties of the base polymer must be high adhesive strength with the heat-sensitive layer, impermeable to oil and plasticizers, and water-soluble but insoluble. We conducted molecular design based on the idea that it is not necessary to be easily soluble, but to be difficult to dissolve in water after being applied to processed paper and dried, and we arrived at the graft copolymer shown below.

In the composition of the graft copolymer according to the present invention, polyvinyl alcohol or copolymerized modified polyvinyl alcohol is used as the backbone polymer to improve wettability to processed paper, make the coated layer uniform, and further improve adhesive strength. By adhering it closely to the processed paper, it increases its effectiveness as a protective layer and imparts oil resistance and plasticizer resistance. By using acrylamide or methacrylamide as a main component as a monomer to be graft copolymerized with this, water solubility and the ability to prevent foaming of an aqueous solution due to the backbone polymer are imparted, and a polymerizable monomer having a carboxyl group is also added. By copolymerizing the branch polymer and introducing carboxyl groups into the branch polymer, the compatibility with the main polymer is increased and performance deterioration due to non-uniformity of the coating film is prevented. Furthermore, a polymerizable monomer having an acetoacetyl group is copolymerized to impart high reactivity with a crosslinking agent, and this is reacted with a crosslinking agent having a functional group such as an aldehyde group or a methylol group. By doing so, a strong three-dimensional network structure can be obtained by crosslinking with the graft copolymer. The coating layer formed by this strengthens the ability to prevent penetration of oil, plasticizers, water, etc.
This further improves its performance as a protective layer. Regarding the weight ratio of the backbone polymer in the graft copolymer and each monomer copolymerized with it, we aim to improve oil resistance and plasticizer resistance by making the coating layer uniform and strengthening the adhesion to processed paper. For this purpose, it is better to increase the ratio of component (A) polyvinyl alcohol or copolymerized modified polyvinyl alcohol, which is the backbone polymer, but if this ratio is increased too much, water resistance will decrease and staining will occur. Sometimes. Furthermore, for the purpose of preventing performance deterioration due to non-uniformity of the graft copolymer film, it is sufficient to increase the ratio of the polymerizable monomer having a carboxyl group, which is component (C).
If this ratio is too high, the water resistance will decrease due to the increase in the hydrophilicity of the copolymer, or the anionic property will become strong, and the miscibility with the inorganic extender pigment that is usually blended in the coating liquid will be reduced. It may be damaged by shots etc. However, when used for applications that do not require very high plasticizer resistance and oil resistance, (C)
Components can also be removed. On the other hand, for the purpose of improving oil resistance, plasticizer resistance, and water resistance by increasing the number of reaction points with the crosslinking agent and increasing the density of the three-dimensional network structure after reaction with the crosslinking agent, component (D) is It is possible to increase the ratio of polymerizable monomers having acetoacetyl groups, but if this ratio is increased too much, the water solubility of the copolymer will decrease, making it impossible to obtain an aqueous solution, and cross-linking between copolymers will occur. The desired copolymer cannot be obtained due to reasons such as increased viscosity and gelation.

As mentioned above, the polyvinyl alcohol or copolymer-modified polyvinyl alcohol that is component (A) has water solubility, compatibility with the branch polymer in the graft copolymer, workability in coating the graft copolymer aqueous solution, The above-mentioned types are selected in order to improve the performance of the graft copolymer, taking into consideration the properties such as the uniformity of the coating layer and the adhesion with processed paper. As the monomer, the above-mentioned types are selected in consideration of normal use and improvement of compatibility between the trunk polymer and the branch polymer. On the other hand, the polymerizable monomer having an acetoacetyl group, which is component (D), should be selected in consideration of its influence on the water solubility, high viscosity, gelation, etc. of the graft copolymer, and its reactivity with the crosslinking agent. , the above types are selected. Further, as the crosslinking agent, the above-mentioned types are selected in consideration of the reactivity with the acetoacetyl group and the influence of the crosslinking agent itself on oil resistance and plasticizer resistance.

Furthermore, as long as the water solubility is not extremely reduced, a part of the (meth)acrylamide component (B) may be mixed with other polymerizable monomers, such as (meth)acrylonitrile, methyl (meth)acrylate, ( Replacement with lower alkyl (meth)acrylates such as ethyl meth)acrylate, hydroxy lower alkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, diacetone acrylamide, etc. You can also

Although there are no particular restrictions on the production of the graft copolymer useful in the present invention, it is usually prepared, for example, by the following method. However, of course, it may be manufactured by other methods.

That is, in an aqueous solution having a concentration of 5 to 35% by weight of polyvinyl alcohol, which is the component (A), to which peroxide is added as a polymerization initiator in advance and the temperature is controlled to boiling or constant temperature, monomers equal to or less than the component (B) are added. Body concentration 30-60
% by weight aqueous solution is quantitatively added dropwise for about 1 to 4 hours to react, and the reaction is further aged for about 2 to 4 hours to complete the reaction. The concentrations of the aqueous solution of component (A) and the aqueous solution of component (B) are preferably adjusted so that the concentration of the graft copolymer obtained by the reaction is 20 to 40% by weight.

The peroxide used as a polymerization initiator is not necessarily limited, but water-soluble ones such as hydrogen peroxide, tert-butyl hydroperoxide, ammonium persulfate, and potassium persulfate are usually suitable. Although there is no particular restriction on the amount of the polymerization initiator used, it is usually desirable to use about 0.1 to 2.0% by weight of peroxide based on the monomer. There are no particular restrictions on the polymerization temperature, but a high temperature is desirable in order to increase the reaction rate and to make the monomer composition distribution of the copolymer uniform.In particular, the boiling point of the reaction solution is most effective, and cooling This is preferable because there is no need for In order for the polymeric protective layer applied as a base polymer for coating liquid and formed on processed paper to have sufficient strength and oil and water resistance, the higher the molecular weight of the polymer, the better. If the molecular weight of the liquid itself is too high, the viscosity will be high and workability will be poor. Relatively high film strength, oil resistant,
For a copolymer liquid that has water resistance and good workability, for example, the viscosity of a 10% aqueous solution at room temperature is approximately 50 to 500CP, and the copolymer aqueous solution is adjusted to have a viscosity within this range. For this purpose, it is necessary to use the amount of the polymerization initiator within the above range. In addition, the ratio of the monomer aqueous solution below component (B) and the polyvinyl alcohol aqueous solution at the time of preparation is such that the viscosity of the copolymer aqueous solution obtained as a result of polymerization is adjusted to a suitable range, and the polymerization rate is increased. The above range is selected from the viewpoint of completing the polymerization in an appropriate amount of time. As mentioned above, the crosslinking agent is water-soluble and stable for a long time in an aqueous solution when mixed with an aqueous solution of the above-mentioned copolymer. The above-mentioned types are selected from the viewpoint that, when formed into a layer, the crosslinking reaction must proceed even at room temperature, and the crosslinking reaction must be completed in a short time at high temperatures. and,
When the above-mentioned graft copolymer and crosslinking agent are mixed, both react and the viscosity increases, so the coating liquid prepared by mixing has a viscosity range suitable for workability during coating. Since the time is limited, it is preferable to apply it to the processed paper used within the pot life. The mixing ratio of the graft copolymer and the crosslinking agent is 100:3 based on the balance between the pot life of the mixed coating liquid and the performance when applied to processed paper to form a protective layer.
~100:30 is preferable, and from the same viewpoint, the pH of the mixed coating liquid and the concentrations of the graft copolymer and the crosslinking agent are preferably 3 to 7 and 10 to 15%, respectively. In this case, the pot life is 20~
It is 300 hours.

In producing the coating liquid for forming a protective layer, in addition to the aqueous solution of the copolymer according to the present invention, if necessary,
Other polymer compounds and fillers such as pigments and waxes can also be blended as appropriate.

Examples of processed paper for which the protective layer forming agent for processed paper according to the present invention can be effectively used include thermal recording paper, photographic paper, and various information recording papers, and it is particularly used for leuco dye-based thermal recording paper. is practically superior.

There are no particular restrictions on the application of the protective layer forming agent coating liquid for processed paper, but usually, for example, the thickness of the protective layer after drying is determined by using a wire bar, roll coater, etc. on the surface of the processed paper to be coated. 1 to 5 μm, and at a temperature of 60 to 75°C under conditions suitable for the processed paper used, for example, for thermal recording paper,
It will dry in 30 seconds to 5 minutes.

In addition, in order to form a protective layer against penetration of chemicals such as plasticizers and oils and water from the back side of the processed paper, it is coated under similar conditions on the back side of the processed paper or on the surface of the base paper before forming the processed layer on the base paper. , dried.

〔Example〕

Hereinafter, the present invention will be explained in more detail by showing typical examples. Of course, the present invention is not limited to these examples. In the examples, parts indicate parts by weight.

Example 1 (a) Method for producing protective layer forming agent In a reactor equipped with a stirrer and a reflux condenser,
Add an aqueous solution of 40 parts of partially saponified polyvinyl alcohol with a degree of polymerization of 1500 and a degree of saponification of 88% dissolved in 335 parts of water, raise the temperature to the boiling point by stirring and heating, and add 1.44 parts of peroxide. and refluxed. A monomer aqueous solution prepared by dissolving 35 parts of acrylamide, 5 parts of acrylic acid, and 20 parts of methacrylic acid 2-acetoacetyloxypropyl ester in 65 parts of water was added dropwise to this solution at such a rate that the entire amount was added dropwise in 1 hour. After the entire amount was added dropwise, the mixture was aged for 2 hours to complete the reaction.
The concentration of the copolymer at this time was 20% by weight, but this was diluted with water to form an aqueous solution having a copolymer concentration of 10% by weight, which was used as a protective layer forming agent. Next, 2.5 parts of glyoxal having a concentration of 40% by weight and 7.5 parts of water were added and dissolved in 100 parts of this aqueous solution. The viscosity of this aqueous solution at a temperature of 20℃ is
It was 200 cp and had a pot life of 48 hours.

(b) Production of coating liquid and application to processed paper () Add 20 parts of calcium carbonate to 100 parts of the aqueous solution obtained in (a) above to make a coating liquid, and apply this to leuco paint-based thermal recording paper. Apply using a wire bar and dry to a protective layer thickness of 2 μm.
A thermosensitive recording paper was obtained.

() The aqueous solution obtained in (a) above was spray coated onto color photographic paper and dried to obtain color photographic paper with a protective layer thickness of 1 μm.

(c) Oil resistance and water resistance test () The thermal recording paper obtained in (b) () was tested at room temperature for 7
After aging for a day, printing was carried out using a heated head, and tempura oil and dioctyl phthalate were respectively applied to the surface. After 24 hours, the density of the printing was measured, but there was no change. Also, when the same heat-sensitive recording paper was immersed in water and traced with a finger 24 hours later, the print did not come off.

(2) After aging the photographic paper obtained in (2) at room temperature for 7 days, templar oil and dioctyl phthalate were applied to the surface, and the color tone was compared after 24 hours, but no change was observed. Also, when the same photographic paper was immersed in water and traced with a finger after 24 hours, there was no change in the surface of the photographic paper.

For comparison, the same tests as above were conducted on leuco dye-based thermal recording paper and color photographic paper that were not coated with the protective layer forming agent of the present invention, but the oil and water resistance effects as described above were not observed. .

Examples 2 to 6 Coating solutions for the various graft copolymer-containing aqueous solutions shown below were prepared in the same manner as in Example 1, applied to leuco dye-based thermal recording paper and color photographic paper, and dried. A similar test was conducted using the following methods, and it was found that both had the same performance as Example 1.

(2) Has a degree of polymerization of 2000 and contains 3% by weight of acrylic acid.
30 parts of copolymerized modified polyvinyl alcohol with a degree of saponification of 99%, 25 parts of acrylamide
10% by weight of a graft copolymer of 25 parts of methacrylamide, 4 parts of methacrylic acid and 16 parts of acrylic acid acetoacetyloxyethyl ester.
10% by weight of dimethylol urea in 100 parts of aqueous solution
Aqueous solution mixed with 10 parts of aqueous solution (viscosity at 20℃
150 cp, pot life 30 hours).

(3) It has a degree of polymerization of 500 and allyl alcohol is 6
50 parts of copolymerized modified polyvinyl alcohol with a degree of saponification of 99%, 25 parts of acrylamide, 5 parts of acrylic acid, and allyl acetoacetate, copolymerized in weight%
20 parts of a 10% by weight aqueous solution of the graft copolymer 100
part, 10% by weight aqueous solution of dialdehyde starch
Aqueous solution mixed with 20 parts (viscosity at 20°C)
100 cp, pot life 100 hours).

(4) 30 parts of polymerized monomer-copolymerized modified polyvinyl alcohol with a degree of saponification of 99%, copolymerized with 15% by weight of monomethyldimethoxyvinylsilane and having a degree of polymerization of 300, 42 parts of methacrylamide, and 3 parts of itaconic acid. An aqueous solution prepared by mixing 5 parts of a 10% by weight aqueous solution of trimethylolmelamine with 100 parts of a 10% by weight aqueous solution of a graft copolymer containing 25 parts of acetoacetyloxyethoxyethyl methacrylate (viscosity 80 cp at 20°C, usable). hours 24
time).

(5) 25 parts of fully saponified polyvinyl alcohol having a degree of polymerization of 500, copolymerized with 5% by weight of N-butylacrylamide having a degree of polymerization of 500;
To 100 parts of a 10% by weight aqueous solution of a graft copolymer of 25 parts of copolymerized modified polyvinyl alcohol, 25 parts of acrylamide, 8 parts of acrylic acid and 17 parts of isobutenyl acetoacetate, 10 parts of an aqueous solution of 5% by weight of glyoxal and 5% by weight of dimethylol urea were added. Aqueous solution mixed with (viscosity 130cp at 20℃, pot life 50
time).

(6) With a degree of polymerization of 1500 and 2% by weight of acrylic acid.
and 10% by weight of a graft copolymer of 25 parts of copolymerized modified polyvinyl alcohol with a degree of saponification of 99%, 52 parts of acrylamide, 3 parts of maleic acid, and 20 parts of allyl acetate, in which 5% by weight of versadic acid was copolymerized. An aqueous solution prepared by mixing 100 parts of an aqueous solution with 20 parts of a 10% by weight aqueous solution of dimethylol acetone (viscosity at 20°C: 250 cp, pot life: 36 hours).

(7) It has a polymerization degree of 2000, copolymerized with diacetone acrylamide at 10%, and a saponification degree of 95%.
To 100 parts of a 10% by weight aqueous solution of a graft copolymer of 40 parts of modified polyvinyl alcohol, 35 parts of acrylamide, 5 parts of acrylic acid and 20 parts of acetoacetyloxyethyl methacrylate, 15 parts of a 10% by weight aqueous solution of dimethylol urea was added. (viscosity 200cp at 20℃, pot life 24 hours).

Claims (1)

[Scope of Claims] 1. At least one of (A) polyvinyl alcohol and/or copolymerized modified polyvinyl alcohol, (B) acrylamide and/or methacrylamide, (C) a polymerizable monomer having a carboxyl group, and ( D) An aqueous solution of a graft copolymer with at least one polymerizable monomer having an acetoacetyl group. 2 (A) polyvinyl alcohol and/or copolymerized modified polyvinyl alcohol, (B) acrylamide and/or methacrylamide, (C) at least one polymerizable monomer having a carboxyl group, and (D) an acetoacetyl group. A processing surface protective layer forming agent for paper containing an aqueous solution of a graft copolymer with at least one polymerizable monomer.