JP6575064B2 - Laminate, thermal recording medium, and inkjet recording medium - Google Patents

Description

  The present invention relates to a laminate having a cross-linked layer containing a paper substrate and a cross-linked product of an acetoacetyl group-containing polyvinyl alcohol resin, and more particularly relates to a laminate having a little yellowing with time of the cross-linked layer. .

  A resin such as polyvinyl alcohol resin (hereinafter referred to as PVA resin) is dissolved in a liquid component such as water to form a coating solution, and the coating solution is applied and dried to make the paper water and oil resistant. The laminated body using paper has a wide variety of uses, such as being used for wrapping paper and tickets, and used as glossy paper for photographic printing.

  The PVA resin used for the coating liquid is excellent in oil resistance and solvent resistance, and thus is used for various applications. Among PVA resins, acetoacetyl group-containing PVA resins (hereinafter referred to as AA-PVA) that can impart water resistance by reacting with a crosslinking agent to form a crosslinked product are widely used.

However, AA-PVA reacts with a cross-linking agent, and when it becomes a cross-linked product, it has a problem of yellowing with time.
Various studies have been conducted on such problems in the past. For example, it has been proposed to incorporate a reducing agent such as sodium bisulfite into a cross-linked structure of AA-PVA and a hydrazine compound (for example, Patent Document 1).
In addition, it has also been proposed to suppress discoloration by irradiating a cross-linked product of AA-PVA and glyoxylate with ultraviolet rays (for example, Patent Document 2).

JP 2009-280754 A JP2013-028697A

However, the technique of Patent Document 1 has a problem that the original physical properties of AA-PVA may be lowered by adding a reducing agent. Moreover, in the technique of patent document 2, since there exists a possibility that another compound may react by irradiating an ultraviolet-ray, the use which can be used was restricted.
Therefore, there is a need for a method for suppressing yellowing over time without adding an additive to the layer containing AA-PVA and a crosslinking agent and without requiring irradiation with active energy rays.

  As a result of intensive investigations in view of the above circumstances, the present inventor, in a laminate containing a cross-linked product layer containing a cross-linked product of a paper base material, AA-PVA and a cross-linking agent, an emulsion having a specific glass transition temperature. It discovered that the above-mentioned subject was solved by coating on a paper base material, and completed this invention.

  In the present invention, since the emulsion having a low glass transition temperature has few voids, the metal (size agent, filler, paper strength enhancer, etc.) contained in the paper base material, which is one of the causes of the yellowing of the cross-linked product layer over time It is presumed that the migration of the metal contained in the additive) to the cross-linked product layer was prevented and yellowing over time could be reduced.

  Since the laminated body of this invention has suppressed the yellowing with time of a crosslinked material layer, the laminated body excellent in external appearances, such as a printing paper and a packaging paper, can be provided.

The laminate of the present invention comprises a paper substrate (A) coated with an emulsion having a specific glass transition temperature and a crosslinked product layer (B) containing a crosslinked product obtained by reacting AA-PVA with a crosslinking agent. It contains.
The description of the constituent requirements described below is an example (representative example) of an embodiment of the present invention, and is not limited to these contents.
Hereinafter, the present invention will be described in detail.

[Paper substrate (A)]
The paper base material (A) of the present invention is obtained by coating an acrylic emulsion having a specific glass transition temperature. The emulsion may be on one side or both sides of the paper. In the case of one side, the cross-linked product (B) side surface is preferred.
The thickness of the paper substrate (A) of the present invention is usually 10 to 2000 μm, preferably 20 to 1000 μm, particularly preferably 30 to 500 μm.
Moreover, the basic weight of a paper base material (A) is 5-1000 g / m < ² > normally, Preferably it is 30-500 g / m < ² >, Most preferably, it is 40-300 g / m < ² >.

First, the emulsion will be described in detail.
{Emulsion}
The glass transition temperature (Tg) of the emulsion used in the present invention is 13 ° C. or lower, preferably −20 to 13 ° C., particularly preferably 0 to 13 ° C.
The glass transition temperature (Tg) is the glass transition temperature of the synthetic resin that constitutes the dispersoid of the emulsion. If the glass transition temperature is too high, the effect of the present invention tends to be difficult to obtain, and if it is too low, the fluidity during drying tends to be high and delamination tends to occur.
As the glass transition temperature (Tg) of the emulsion of the present invention, the value calculated by the Fox equation shown in the following equation (1) is used.

1 / Tg = W ₁ / Tg ₁ + W ₂ / Tg ₂ +... + W _n / Tg _n (1)
In the above formula (1), W _n from W ₁ represents the weight fraction of each monomer using, Tg _n from Tg ₁ is the glass transition temperature (unit of a homopolymer of each monomer Indicates an absolute temperature “K”). The absolute temperature is calculated as absolute temperature “K” = Celsius temperature “° C.” + 273.15.

  The dispersoid of such an emulsion is usually a polymer obtained by polymerizing at least one unsaturated monomer selected from ethylenically unsaturated monomers and diene monomers, and such ethylenically unsaturated monomers. Examples of the monomer and diene monomer include monomers frequently used in emulsion polymerization, such as vinyl ester monomers, acrylic acid or its ester monomers, diene monomers, and the like, and other monomers include olefins. Examples thereof include a series monomer, an acrylamide monomer, an acrylonitrile monomer, a styrene monomer, a vinyl ether monomer, and an allyl monomer.

Such vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, and acrylic acid or its ester monomers include methyl (meth) acrylate, ethyl (meth) acrylate, and (meth) acrylic acid n. Examples of the diene monomer include -propyl, i-propyl (meth) acrylate, n-butyl (meth) acrylate, and the like. Examples of the diene monomer include butadiene-1,3 and 2-methylbutadiene.
Furthermore, examples of the olefin monomer include ethylene, propylene, 1-butene, and isobutene, and examples of the acrylamide monomer include (meth) acrylamide, N-methylolacrylamide, N, N-dimethylacrylamide, and the like.
Of these, (meth) acrylic monomers are preferred.
In addition, the above ethylenically unsaturated monomers and diene monomers can be used alone for polymerization, but it is of course possible to mix two or more types for polymerization (copolymerization). is there.

Next, the manufacturing method of the aqueous emulsion of this invention is demonstrated.
In order to obtain an aqueous emulsion, there are methods such as emulsion polymerization and post-emulsification. In carrying out the former emulsion polymerization, a) an ethylenically unsaturated monomer in the presence of water, a surfactant and a polymerization catalyst. And / or a conventional emulsion polymerization method in which a diene monomer is added temporarily or continuously, followed by heating and stirring, and b) an ethylenically unsaturated monomer in the presence of water, a surfactant and a polymerization catalyst. An emulsion polymerization method in which a dispersion (pre-emulsion) obtained by mixing and dispersing a body and / or diene monomer in an aqueous solution of a surfactant is added temporarily or continuously, followed by heating and stirring can be carried out.

  Furthermore, examples of the surfactant include alkyl or alkyl allyl sulfate, alkyl or alkyl allyl sulfonate, dialkyl sulfosuccinate, sodium dodecyl benzene sulfonate, sodium polyoxyethylene alkyl ether sulfate, sodium alkyl sulfonate, and the like. Anionic surfactants of: cationic surfactants such as alkyltrimethylammonium chloride and alkylbenzylammonium chloride; polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene carboxylic acid ester, polyoxyethylene glycol type, Nonionic surfactants such as polyoxyethylene propylene glycol type; and ammonium = α-sulfonato-ω-1- (allyloxymethyl) L) Alkyloxypolyoxyethylene, α-sulfo-ω- (1- (alkoxy) methyl-2- (2-propenyloxy) ethoxy-poly (oxy-1,2-ethanediyl) ammonium salt, polyoxyethylene alkyl Examples thereof include propenyl phenyl ether, and these are used alone or in combination of two or more.

  The amount of the surfactant used is not particularly limited, but is preferably 0.1 to 10 parts, more preferably 0.5 to 5 parts, based on 100 parts of the whole ethylenically unsaturated monomer. A range is preferable. That is, if the amount of the surfactant used is too small, the polymerization stability tends to become unstable. Conversely, if the amount is too large, the average particle size of the resulting copolymer tends to be too small. This is because, as a result, there is a tendency that problems such as a decrease in workability due to an excessive increase in the viscosity of the emulsion composition are observed.

As the polymerization initiator, usually potassium persulfate, ammonium persulfate, potassium bromate, etc. are used alone or in combination with acidic sodium sulfite, and further hydrogen peroxide-tartaric acid, hydrogen peroxide-iron salt, peroxide Water-soluble redox polymerization initiators such as hydrogen-ascorbic acid-iron salt, hydrogen peroxide-longalite, hydrogen peroxide-longalit-iron salt are used.
The addition method of the polymerization initiator is not particularly limited, and a method of adding all at once in the initial stage, a method of adding continuously as the polymerization progresses, or the like can be employed.

  Moreover, a polymerization inhibitor, a dispersion stabilizer, a pH adjuster, etc. can also be mix | blended as needed.

The solid content concentration of the emulsion of the present invention is usually 10 to 65% by weight, preferably 20 to 60% by weight, particularly preferably 30 to 50% by weight.
In addition, when the solid content concentration of the emulsion is high, it is preferable to add water to the emulsion at the time of coating to obtain an emulsion coating solution. In this case, the solid content concentration is 0.5 to 60% by weight, preferably 2 to 40% by weight, particularly preferably 5 to 20% by weight.
If the concentration of the emulsion coating solution is too low, a film forming defect tends to occur when the film thickness is thin, and a drying defect tends to occur when the film thickness is thick. On the other hand, if the concentration is too high, the viscosity of the emulsion coating solution tends to increase, making coating difficult.
As the coating weight, 0.01 to 100 g / m ² at normal solids, preferably from 0.2 to 50 g / m ^2, particularly preferably 0.5 to 10 g / m ^2. If the amount is too small, the effect of the present invention tends to be difficult to obtain. If the amount is too large, the paper substrate becomes hard and winding failure tends to occur.

  The drying temperature after coating the emulsion is usually 5 to 150 ° C, more preferably 30 to 120 ° C, particularly 40 to 110 ° C, and 0.1 to 60 minutes, more preferably 1 to 30. Minutes, in particular, a drying time of 2 to 20 minutes is preferably used.

In addition, as a method for obtaining an emulsion having a glass transition temperature of 80 ° C. or lower, it is possible to adjust Tg by changing the kind of polymer monomer as a dispersoid and the ratio in the case of copolymerization. . For example, in the case of an acrylic emulsion, (meth) acrylic acid and an ester monomer having an alkyl group are used as monomers. Examples of such monomers include aliphatic (meth) acrylates having 1 to 10 carbon atoms in the alkyl group, such as butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, methyl (meth) acrylate, and cyclohexyl (meth) acrylate. It is done.
Examples of acrylic emulsions having a Tg of 80 ° C. or less include Movinyl 7720 (manufactured by Nippon Synthetic Chemical Co., Ltd., Tg = 4 ° C.), Movinyl 7820 (manufactured by Nippon Synthetic Chemical Co., Ltd., Tg = 4 ° C.), Movinyl DM772 (manufactured by Nippon Synthetic Chemical Co., Ltd.). Tg = 13 ° C.), mobile DC02 (manufactured by Nippon Synthetic Chemical Co., Ltd., Tg = 30 ° C.), and the like.

{paper}
Paper is usually printed on paper such as Manila balls, white balls, liners, general high quality paper, medium quality paper, gravure paper, upper / middle / lower grade paper, newsprint, release paper, carbon paper, non-carbon paper, Examples include glassine paper.

[Crosslinked product layer (B)]
The crosslinked product layer (B) contains a crosslinked product obtained by reacting AA-PVA with a crosslinking agent, and the AA-PVA and the crosslinking agent will be described in this order.

{AA-modified PVA}
Next, the AA-PVA used in the present invention will be described.
The AA-PVA used in the present invention is one in which an acetoacetyl group (AA group) is bonded to the main chain of the PVA resin directly or through an oxygen atom or a linking group, and is represented by, for example, the general formula (3). And a polyvinyl alcohol resin containing a structural unit having an AA group. In addition, this AA-ized PVA has a vinyl alcohol structural unit in addition to the structural unit having an AA group, and further has a vinyl ester structural unit of an unsaponified portion.

  The average degree of polymerization of the AA-PVA of the present invention (based on JIS K6726) may be appropriately selected depending on the application, but is usually 300 to 4000, particularly 400 to 3500, and more preferably 500 to 3000. Used. If the average degree of polymerization is too small, sufficient water resistance may not be obtained or a sufficient crosslinking rate may not be obtained. On the other hand, if it is too large, the viscosity becomes too high when used as an aqueous solution. Application to various processes tends to be difficult, for example, coating on a substrate becomes difficult.

  The saponification degree of the AA-PVA used in the present invention is usually 80 to 100 mol%, more preferably 85 to 99.9 mol%, and particularly preferably 90 to 99.8 mol%. Used for. When the degree of saponification is low, it tends to be difficult to make an aqueous solution, the stability of the aqueous solution is lowered, and the water resistance of the obtained crosslinked polymer tends to be insufficient.

  Further, the AA group content (hereinafter abbreviated as AA degree) in the AA-modified PVA is usually 0.1 to 20 mol%, further 0.2 to 15 mol%, and particularly 0.3. What is 10 mol% is generally used widely. If the content is too small, sufficient water resistance tends to be insufficient, or a sufficient crosslinking rate tends not to be obtained. On the other hand, if the content is too large, water solubility decreases or the stability of the aqueous solution decreases. Tend to.

In the present invention, it is preferable that all of the PVA-based resins to be used are AA-PVA, but PVA-based resins other than AA-PVA may be used in combination, and the content thereof is based on AA-PVA, It is usually 20% by weight or less, particularly preferably 10% by weight or less, and more preferably 5% by weight or less.
Examples of PVA resins other than the AA-modified PVA resin include unmodified PVA resins and various modified PVA resins obtained by copolymerizing various monomers having copolymerizability with the above-mentioned vinyl ester monomers. Can be mentioned.

  In addition, the AA-PVA of the present invention includes an alkali metal acetate such as sodium acetate used or produced as a by-product in the production process (mainly by saponification of alkali metal hydroxide and polyvinyl acetate used as a saponification catalyst). Organic acid such as acetic acid (derived from an organic acid occluded in PVA during reaction with diketene when introducing an acetoacetate group into a PVA resin), methanol In addition, a part of the organic solvent such as methyl acetate (derived from the reaction solvent of PVA resin, the cleaning solvent during the production of AA-PVA) may remain.

  As a method for producing such AA-PVA, it can be produced by the method described in paragraphs [0059] to [0065] of JP2010-077385.

{Crosslinking agent}
AA-modified PVA needs to contain a crosslinking agent to improve water resistance. Aldehyde compounds such as glyoxal generally used in PVA, organic salts of hydrazine, hydrazine compounds such as adipic acid dihydrazide, Examples thereof include metal salts of glyoxylic acid, methylol compounds such as methylolated melamine, and metal compounds such as basic zirconium chloride. Adipic acid dihydrazide is preferably used from the viewpoint of reaction rate.
Although content of this crosslinking agent is based also on the kind of crosslinking agent, it is 0.5-30 weight part normally with respect to 100 weight part of AA-ized PVA, Preferably it is 1-20 weight part, More preferably, it is 2-15 weight part It is. If the content of such a crosslinking agent is too much or too little, the water resistance tends to decrease.

{Coating liquid for cross-linked product}
The cross-linked product layer (B) of the present invention is obtained by applying the AA-PVA as an aqueous solution, coating a cross-linking agent and various additives to obtain a cross-linked product coating solution, and drying. .
The concentration of the AA-PVA aqueous solution is usually 1 to 50% by weight, preferably 2 to 30% by weight. If the content is too small, the effect as a crosslinked product layer may not be sufficiently exhibited. On the other hand, if the amount is too large, the viscosity of the coating solution increases, which may make coating difficult and is not preferable.

  Moreover, as pH of the coating liquid for crosslinked material layers, 10 or less are preferable, and also it is 3-10. If the pH is too high, the hot water resistance and plasticizer resistance may decrease, which is not preferable. In addition, since AA-PVA becomes weakly acidic when made into an aqueous solution, such pH adjustment is usually not necessary. However, if necessary, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, citric acid, tartaric acid, succinic acid, acetic acid The pH may be adjusted with an organic acid such as sodium hydroxide, or a basic compound such as sodium hydroxide, potassium hydroxide, sodium bicarbonate, or ammonia.

Furthermore, an inorganic filler, a thermoplastic resin, a pigment, other additives, etc. can also be mix | blended with a coating liquid as needed.
Examples of the inorganic filler include kaolin, silica, calcium hydroxide, and aluminum hydroxide.
Examples of the thermoplastic resin include acrylic resins, polyester resins, polyvinyl chloride resins, saponified ethylene-vinyl acetate copolymers, and acrylic resins are preferred from the viewpoint of ink adhesion.
The blending amount of the thermoplastic resin is usually 10 to 70% by weight, preferably 20 to 60% by weight, based on the total solid content of the coating liquid.
Examples of the pigment include organic pigments such as nylon resin fillers, urea / formalin resin fillers, and starch particles. Other additives include lubricants such as zinc stearate, calcium stearate, and paraffin wax, and surfactants. Agents, ultraviolet absorbers, fluorescent dyes, release agents, antioxidants, and the like.

  Moreover, as drying conditions after apply | coating the coating liquid for crosslinked material layers, it is 5-150 degreeC normally, Furthermore, it is 30-150 degreeC, Especially 50-150 degreeC temperature conditions, 0.1-60 Minutes, more preferably 0.1 to 30 minutes, in particular 0.2 to 20 minutes.

The cross-linked product layer (B) obtained by applying the cross-linked product coating solution of the present invention is coated with the cross-linked product coating solution on the paper substrate (A) and dried. It is formed by.
The thickness of the crosslinked product layer (B) is usually 0.01 to 100 μm, preferably 0.05 to 20 μm, and particularly preferably 0.1 to 10 μm.

[Thermal recording medium]
The laminate of the present invention can also be used as a thermal recording medium. When used as a thermal recording medium, a thermal coloring layer is provided between the paper substrate (A) and the cross-linked product layer (B).
The thermosensitive coloring layer will be described below.

{Thermosensitive coloring layer}
The thermosensitive coloring layer is obtained by obtaining an aqueous solution (coloring solution) obtained by further mixing a coloring material and a developer with a binder (for example, polyvinyl alcohol, methylcellulose, carboxymethylcellulose, starches, latex, etc.). It can be formed by coating the material.
Such a heat-sensitive color developing layer may be obtained by obtaining an aqueous solution in which a binder, a color developing material and a developer are blended, and then applying the aqueous solution to a substrate. At this time, the color-developing substance and the developer are blocked in an aqueous solution and are pulverized to about 0.1 to 5 μm by a sand grinder, ball mill, visco mill, bead mill or the like.

[Inkjet recording medium]
The laminate of the present invention can also be used as an ink jet recording medium. When used as an inkjet recording medium, the crosslinked product layer can be used as an ink receiving layer by containing an inorganic filler in the crosslinked product layer. Further, a known gloss layer may be coated on the ink receiving layer.

  Furthermore, in the ink receiving layer using the crosslinked product layer of the present invention, a pigment dispersant, a thickener, a fluidity improver, a surfactant, a reducing agent, and an antifoaming agent are provided as long as the object of the present invention is not impaired. , Mold release agents, penetrants, dyes, pigments, ultraviolet absorbers, antioxidants, preservatives, paper strength enhancers, and the like may be blended.

Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the description of the examples unless it exceeds the gist.
In the examples, “parts” and “%” mean weight basis unless otherwise specified.

Example 1
[Preparation of paper substrate (A1)]
An acrylic emulsion (Mobil DM772 glass transition temperature 13 ° C., manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was diluted with water to obtain an emulsion coating solution 1 having a solid content of 20% by weight. The emulsion coating solution 1 is coated on a copy paper (thickness 57 μm, basis weight 64 g / m ² ) with an applicator having a clearance of 100 μm, dried at 70 ° C. for 5 minutes, and then a paper substrate (A1) Got. The coating amount of the solid content of the emulsion was 2 g / m ² .

[Preparation of laminate 1]
{Create AA PVA}
100 parts of PVA resin (saponification degree: 98.0 mol%, average tenth degree: 2400) was charged into a kneader, 30 parts of acetic acid was added thereto, and the mixture was swollen and stirred at a rotation speed of 20 rpm, while being kept at 60 ° C. After heating, 5 parts of diketene was added dropwise over 5 hours, and the reaction was further continued for 1 hour. After completion of the reaction, it was washed with methanol and then dried at 70 ° C. for 12 hours to obtain AA-modified PVA. The AA degree of this AA-ized PVA is 4.5 mol%, and the saponification degree and the average tenth degree are the same as the PVA resin used.
{Crosslinking reaction}
After blending 5 parts of adipic acid dihydrazide with 100 parts of the 10% aqueous solution of AA-PVA obtained above and mixing, it was coated on the paper substrate 1 obtained above with an applicator having a clearance of 50 μm, and 70 ° C. And dried for 5 minutes to obtain a laminate 1 of the present invention.

[Coloring evaluation]
The laminated body 1 obtained above was promoted for coloring for 28 days with a constant temperature and humidity machine at 40 ° C. and 90% RH. Color measurement was performed with a colorimeter. As a measuring apparatus, a spectrocolorimeter CM-3600A (manufactured by Konica Minolta Sensing) was used, and the reflection method light source D-65 was evaluated with an average value of N = 3.
The results are shown in Table 1.

Example 2
[Creation of paper substrate (A2)]
Instead of the emulsion coating liquid 1 of Example 1, an acrylic emulsion 2 (Nippon Gosei Kagaku Co., Ltd. Movinyl 7820 glass transition temperature 4 ° C.) was diluted with water to give an emulsion coating liquid 2 having a solid content of 20% by weight. A paper substrate (A2) was obtained in the same manner as in Example 1 except that it was used. The coating amount of the solid content of the emulsion was 2 g / m ² .

[Coloring evaluation]
In Example 1, color evaluation was performed in the same manner as in Example 1 except that the paper base (A1) was changed to the paper base (A2). The results are shown in Table 1.

Comparative Example 1
[Preparation of paper substrate (A3)]
Instead of the emulsion coating liquid 1 of Example 1, acrylic emulsion 3 (Nippon Gosei Kagaku Co., Ltd. Movinyl 972 glass transition temperature 101 ° C.) was diluted with water to obtain an emulsion coating liquid 3 having a solid content of 20% by weight. A paper substrate (A3) was obtained in the same manner as in Example 1 except that it was used. The coating amount of the solid content of the emulsion was 2 g / m ² .

[Coloring evaluation]
In Example 1, the color evaluation was performed in the same manner as in Example 1 except that the paper base (A1) was changed to the paper base (A3). The results are shown in Table 1.

In Examples 1 and 2 using the laminate of the present invention, the Δb ^* value was small, and yellowing over time was small. On the other hand, in Comparative Example 1 in which the laminate of the present invention was not used, the Δb ^* value was large and the yellowing over time was large.

  The laminate of the present invention has little yellowing in the course and is useful for heat-sensitive recording media and inkjet recording media.

Claims (3)

A laminate having a crosslinked product layer (B) containing a crosslinked product obtained by reacting a paper substrate (A) and an acetoacetyl group-containing polyvinyl alcohol resin with a crosslinking agent,
A laminate comprising the paper base (A) coated with an acrylic emulsion having a dispersoid polymer having a glass transition temperature of 13 ° C. or lower. The heat-sensitive recording medium comprising the laminate according to claim 1, wherein a heat-sensitive recording layer is provided between the paper substrate (A) and the crosslinked material layer. The ink jet recording medium comprising the laminate according to claim 1, wherein the crosslinked product layer (B) is an ink receiving layer.