JPH09124975A - Aqueous coating composition and coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film good in ink transferring properties and writing quality by applying an aqueous coating agent made up of an aqueous polymer dispersion and a polyvinyl alcohol having a specified degree of polymerization on a plastic film. SOLUTION: (A) An aqueous polymer dispersion is amount of 100 pts.wt. solid content and (B) 10 to 50 pts.wt. aqueous solution of polyvinyl alcohol having a degree of saponification of 95mol.% or more and a degree of polymerization of 40 to 1,200 are mixed to obtain an aqueous coating agent. If an inorganic or organic filler is added thereto, the hiding power and the whiteness can be improved. As the component (A), for example, an alkali metal salt of an ethylene/methacrylic acid copolymer or a methacrylic acid/methyl methacrylate copolymer is used. The resultant coating agent is applied to a plastic film followed by drying to obtain a film good in ink transferring properties and ink hold-out and having performance, strength, and water resistance close to those of natural pulp paper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic film which is excellent in ink transferability, ink retention (a property that ink does not easily soak and rub), writability and generates little paper dust, and an aqueous coating composition used therefor.

[0002]

[Prior art and its problems] Instead of natural pulp papermaking, plastic raw materials such as polypropylene are mixed with inorganic fine powder, and in the process of forming a film, the internal structure such as a delicate cavity and the film surface are formed. Synthetic paper that has fine concavities and convexities and has concealing properties, whiteness, and writing properties has been put into practical use. The uneven structure of the surface has the function of improving not only the writing property but also the transferability of the ink and the holding property of the ink.However, since the synthetic paper made by this method has fine surface unevenness, these performances are sufficient. is not.

In Japanese Patent Laid-Open No. 62-53345, further, inorganic fine powder is mixed with a binder such as polyvinyl acetate and coated on a film. However, in this method, when the amount of the binder is large, the uneven structure is filled, and on the contrary, when the amount of the binder is small, fine powder easily falls (so-called paper dust is generated), and as a result, It is difficult to obtain a sufficient uneven structure. Further, in particular, when a water-soluble resin is used as a binder in consideration of the permeation property of the water-based ink, the binder and the ink easily flow on contact with water and are not suitable for outdoor use.

The object of the present invention is to use a plastic film as a base material, to provide an ink transfer property and an ink holding property which are difficult to obtain by the conventional method, and to impart writability to give a performance close to that of paper. It is to provide a coated film having water resistance.

[0005]

SUMMARY OF THE INVENTION An outline of the present invention is to provide an aqueous coating composition comprising a polymer aqueous dispersion such as a polyolefin aqueous dispersion or an acrylic acid polymer emulsion and polyvinyl alcohol, and further to this composition. It is a film in which a composition to which inorganic and organic fillers have been added is applied onto a plastic film.

When a polyvinyl alcohol aqueous solution is mixed with an aqueous polyolefin dispersion or an acrylic acid polymer emulsion, and the solution is applied onto a film and dried, a special structure having fine gaps is formed on the surface thereof (FIG. 1). This structure is above a certain level (about 5 microns)
Has a function of soaking in the ink, and improves the ink transfer property and the ink retention property. Furthermore, by adding an inorganic filler and an organic filler fine powder to this mixed liquid, it is possible to impart writability, hiding power, and whiteness,
Ink transfer properties and ink retention properties are also improved. When a filler is added, the resin surrounds the filler so that the particles are less likely to fall than those produced by the conventional method (FIG. 2).

Examples of the a) polyolefin aqueous dispersion include an ionomer aqueous dispersion which is an aqueous dispersion of an alkali metal salt of an ethylene-methacrylic acid copolymer. The content of methacrylic acid in the ethylene-methacrylic acid copolymer is usually 10 to 50 mol%, preferably 20 to 30 mol%, from the viewpoint of easy formation of the uneven pattern and miscibility with the polyvinyl alcohol aqueous solution. The particle size of the dispersion is 0.5 μm or less, preferably 0.1 μm or less. Examples of the acrylic acid polymer emulsion include methacrylic acid-methyl methacrylate copolymer. The content of methyl methacrylate in the methacrylic acid-methyl methacrylate copolymer is preferably 35 to 60 mol%, more preferably 40 to 55 mol%. The particle size of the emulsion is 0.5 μm or less,
It is preferably 0.1 μm or less. Even an aqueous dispersion of another polymer can be appropriately selected and used as long as the object of the present invention is not impaired.

Examples of polyvinyl alcohol include resins having a saponification degree of 95 mol% or more and a polymerization degree of 400 to 1200. Among these, the degree of saponification is 98 mol% or more and the degree of polymerization is 5
Those having a size of from 0 to 1000 are preferred in terms of the size of the uneven pattern and the fact that they do not significantly thicken or gel when mixed with the ionomer dispersion or the acrylic acid polymer emulsion. It is preferable that polyvinyl alcohol is mixed in advance as an aqueous solution, and the mixing ratio is 100 parts by weight of a polymer aqueous dispersion solid content such as an ionomer dispersion or an acrylic acid polymer emulsion in terms of easy formation of the uneven structure. 10 to 90 parts by weight is preferable, and 25 to 70 parts by weight is more preferable.

As the filler to be added, both inorganic and organic substances can be used. Examples of the inorganic filler include carbonates, hydroxides, and silicates. Among them, titanium oxide is preferable because it improves whiteness and hiding power. Examples of the organic filler include acrylic, styrene, and urethane particles, and hollow fine particles are preferable when whiteness and hiding power are required. These inorganic fillers and organic fillers may be used alone or in combination of two or more. The size of the filler is preferably 0.5 to 10 μm, and more preferably 1 to 8 μm from the viewpoint of writability and the difficulty of dropping particles. Further, the size of the filler is preferably changed depending on the shape, hardness and coating amount of the filler. Smaller ones are better for square and hard fillers and larger ones for rounded fillers. When whiteness and hiding power are required, a filler having a hiding power smaller than that may be mixed. The amount of filler added depends on the above a) + because it is easy to write and the filler does not easily fall.
The amount is preferably 5 to 300 parts by weight, more preferably 50 to 200 parts by weight, based on 100 parts by weight of the solid content of b).

In order to improve the wettability with the base film, an organic solvent such as cellosolve, a viscosity modifier, a fungicide and the like can be added to the aqueous coating composition of the present invention. The concentration of the aqueous coating composition is preferably high as long as it does not hinder the coating. It is usually 10 to 50%, preferably 20 to 40%. The optimum viscosity varies depending on the coating method and the production speed, but for gravure roll coating, for example, 200 cps or less is preferable.

As the film to which the aqueous coating composition of the present invention is applied, any film can be used as long as it is a plastic film. For example, a polyethylene film, a polypropylene film, a polyolefin film such as a poly-4-methylpentene-1 film, a polyethylene terephthalate film, a polyamide film, a polyvinylidene chloride film, a polycarbonate film and the like are exemplified. These films may be monolayer films or laminated films of the same or different films. Among these, polyolefin film,
Particularly, a uniaxial or biaxial polypropylene film is preferably used. The thickness of the film is usually 15 to 200 μm
It is. The film is preferably subjected to a pretreatment such as a corona treatment in advance. When the hiding property is required, it is possible to use a hiding property film as the base material film, for example, a synthetic paper or an aluminum vapor deposition film produced by an internal paper making method.

In order to improve the adhesiveness of the film obtained by drying the film and the aqueous coating composition, an isocyanate-based adhesive or the like can be applied to the base film as an undercoating agent. The coating amount is preferably 50 to 150 mg / m ² in terms of solid content weight from the viewpoint of adhesive performance and cost.
After the primer is applied and dried, the composition is applied thereon. The coating amount of the composition is 3 to 15 in terms of solid content from the viewpoint that a sufficient uneven structure is obtained and productivity is not reduced.
g / m ² good, more preferably 5 to 10 g / m ^2. The thickness of the film obtained by drying the aqueous coating composition is 3-20 microns, preferably 5-15 microns. However, when using a transparent or semi-transparent substrate film to enhance the hiding property of the coat film, titanium oxide as described above, particles having hiding power such as hollow fine particles are added to the mixed solution in a large amount, and coating is performed. Increasing the amount is effective.

The drying temperature of the film coated with the aqueous coating composition of the present invention is 60 to 150 ° C., especially 70 to 150 ° C.
110 ° C is good. The uneven structure formed by drying at low temperature becomes finer, and the ink transfer property and the ink retention property are improved. If the temperature is lower than that, a film is not formed, or a long drying time is required in the production, which lowers productivity. On the other hand, if the temperature is too high, the pattern becomes rough and the resin melts to collapse the unevenness, which is not preferable. The drying temperature may be determined in consideration of the heat resistance of the base film.

As the method for applying the aqueous coating composition, those conventionally used can be used. Examples include gravure roll coating, Meyer bar coating, doctor blade coating, reverse roll coating, air knife coating and the like. Of these, gravure coating is particularly preferable.

[0015]

Next, the present invention will be described in more detail with reference to Examples 1 to 6. The test film was prepared as follows. As a base material, a biaxially oriented polypropylene film having a thickness of 20 μ and having one surface subjected to corona treatment was used.
First, 100 mg / m ² of a solid content weight of an isocyanate-based adhesive (Takenate A-3 manufactured by Takeda Pharmaceutical Co., Ltd. diluted with ethyl acetate to a solid content of 10%) was applied to the corona-treated surface of the film using a Meyer bar. And dried at 90 ° C. for 5 seconds. As the coating liquid, the following liquids A to G were mixed in a solid content weight ratio as shown in Table 1. These liquids were applied at a solid content of 5 g / m ² using a Meyer bar and dried at 90 ° C. for 40 seconds.
A dryer was used for drying. Then, the test film was left to stand in an oven at 40 ° C. for 24 hours, and each test film was tested. The results shown in Table 1 were obtained.

The liquids A to G used in the examples are as follows. A: ionomer aqueous dispersion methacrylic acid content 20 mol%, average particle size 0.1 μm, solid content 28% B: acrylic acid polymer emulsion methacrylic acid-methyl methacrylate copolymer (methyl methacrylate content 50 mol%), Average particle size 0.1μm, solid content 4
0% C: polyvinyl alcohol aqueous solution PVA-105 (saponification degree 98.5 mol%, degree of polymerization 500) manufactured by Kuraray Co., Ltd.,
Solid content 10% D: Polyvinyl alcohol aqueous solution PVA-110 (saponification degree 98.5 mol%, polymerization degree 1000) manufactured by Kuraray Co., Ltd.,
Solid content 10% E: Polyvinyl acetate emulsion Polysol SH-502 manufactured by Showa Highpolymer Co., Ltd. Solid content 50
% F: Organic filler Acrylic particle dispersion made by Tohcello, average particle size 4.4
μm, solid content 30% G: Inorganic filler Sumitomo Color's Pollux White PM-A average particle size 0.4 μm, solid content 55%

The method of each test and the method of showing the evaluation results are as follows.

(1) Writability test This test evaluates writability. The surface of the test film was written with a pencil of hardness HB under normal writing pressure, and the line was visually observed. The evaluation results were shown as follows. ○ The thickness and thickness of the line are appropriate. △ The line is thin and difficult to see.

(2) Stamp Suitability Test This test evaluates ink transferability and ink retention. Ink the rubber stamp of the character from the stamp stand (Shachihata sol stamp stand) and imprint it on the test film. Immediately after imprinting, the transferred character was lightly rubbed with a finger, and the state of the rubbed character was visually observed. This experiment was conducted in a room at 20 ° C. and RH of 60%. The evaluation results were shown as follows. ○ Characters are dark and clearly visible △ Characters are rubbed or blurred and difficult to see × Characters are rubbed and unreadable

(3) Tape peeling test This test evaluates the retention of the added fine particles. An adhesive tape (Nichiban Cello tape 16 mm width) was strongly pressed against the surface of the test film, and then this tape was strongly peeled off, and the surface was observed with an electron microscope. The evaluation results were shown as follows. ○ No change △ Small amount of fine particles missing × Many fine particles missing

(4) Water resistance test This test evaluates the water resistance of the coating film. The test film was immersed in water at 23 ° C. for 24 hours, then taken out, the coated surface was rubbed with a finger several times, and the change in the appearance of the coated film was visually observed. The evaluation results were shown as follows. ○ No change × Membrane dissolves

(5) Measurement of light transmittance This test evaluates the hiding power of the film. The light transmittance of one film was measured with a turbidimeter (NDH-300A manufactured by Nippon Denshoku Industries Co., Ltd.). The smaller this value is, the better the hiding property is.

[0023]

COMPARATIVE EXAMPLE Next, Comparative Examples 1 to 5 will be shown and described in more detail. Preparation of test film The method of each test and the method of showing the evaluation results were the same as those in the examples, and Table 1 shows these results.

[Table 1]

[0024]

EFFECT OF THE INVENTION The uneven structure formed by applying a mixed solution of a polymer aqueous dispersion such as a polyolefin aqueous dispersion or an acrylic acid polymer emulsion and a polyvinyl alcohol aqueous solution onto a film and drying the film has a certain thickness. It has the ability to permeate ink, and has excellent ink transferability and ink retention during stamping. Further, by adding a filler, the hiding property, whiteness, writing property, ink transfer property, and ink holding property can be improved, and performance similar to that of natural pulp paper can be obtained.

Further, if a polyolefin film is used as the base material, it can have mechanical strength and water resistance which are not available in conventional paper. Therefore, this film is suitable for being used outdoors, and is effective for, for example, slips for home delivery, envelopes, labels, memo papers, and the like. This film also
Since it does not easily generate paper dust, it can be used in clean rooms, etc., and has little impact on printing machines, personal computer printers, etc.

[Brief explanation of the table]

[Table 1] Composition of aqueous coating composition and physical properties of coated film

[Brief description of the drawings]

FIG. 1 is a photomicrograph (SEM photo) of the surface of the coated film of Example 2 at a magnification of 2000 times.

FIG. 2 is a photomicrograph (SEM photo) of the surface of the coated film of Example 4, magnified 1000 times.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C09D 133/02 PFW C09D 133/02 PFW 201/00 PDD 201/00 PDD

Claims (4)

[Claims] 1. A) 100 parts by weight of a polymer aqueous dispersion solid content, b) a saponification degree of 95 mol% or more, and a polymerization degree of 400 to 120.
0 to 90 parts by weight of 0. polyvinyl alcohol, 2. The aqueous coating composition according to claim 1, wherein the aqueous polymer dispersion comprises a polyolefin aqueous dispersion or an acrylic acid polymer emulsion. 3. An inorganic filler and / or an organic filler is added.
The aqueous coating composition according to claim 1 or 2, further comprising ˜300 parts by weight. 4. A film obtained by applying and drying the aqueous coating composition according to claim 1 on at least one side of a plastic film.