JPH0450920B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a printing sheet having a porous printing ink adsorption layer and a method for manufacturing the same. The purpose of the present invention is to easily provide printing sheets that particularly require water resistance.

Conventionally, various types of printing sheets include those in which the substrate itself has printing ink adsorption properties, those in which the substrate has a printing ink adsorption layer mainly made of filler on its surface, and those in which the substrate has a synthetic resin porous Some are known to have a printing ink adsorption layer made of a substrate, and others have a porous printing ink adsorption layer made of a synthetic resin and a filler on a substrate. When these printing sheets are used as various display labels or advertising banners used outdoors, particularly excellent bending resistance, flexibility, water resistance, wash resistance, etc. are required. As the substrate, various woven fabrics are more suitable than paper-based substrates, and for this purpose, for example, polyamide resin or polyurethane resin is dissolved in a hydrophilic organic solvent along with other additives using a woven fabric made of polyester or polyamide fibers as the substrate. A printing sheet has been developed in which an ink adsorption layer is formed by coating a composition on the surface of a substrate and then forming a film by a wet method. However, in the case of such printing sheets, the manufacturing method is a so-called wet film formation method, which requires a dipping process, a cleaning process, a solvent recovery process, a wastewater treatment process, etc., and is extremely costly. In addition, in terms of product quality, due to the wet method, the adhesive strength between the substrate and the adsorption layer is insufficient, resulting in poor bending resistance,
It has poor wash resistance, lacks surface smoothness of the adsorption layer, insufficient printability, and when polyamide resin is used, there are problems with dimensional stability.
It has drawbacks such as not being able to be used for multicolor offset printing, which requires precision.

As a result of intensive research to solve the above-mentioned drawbacks of the prior art, the present inventors found that when forming a printing ink adsorption layer using a specific polyurethane composition, the above-mentioned drawbacks of the production method of the prior art and The present invention was completed based on the finding that the quality defects could be solved at the same time and that a printing sheet with excellent physical properties could be obtained.

That is, the present invention comprises a sheet substrate and a porous printing ink adsorption layer covering at least one surface of the substrate, and the ink adsorption layer is a porous printing ink adsorption layer formed from a water-in-oil polyurethane emulsion. A printing sheet characterized by having a polyurethane layer, and a method for producing the same.

To explain the present invention in detail, the base sheet used in the present invention includes, for example, synthetic fibers such as polyester fibers, polyamide fibers, and acrylic fibers, woven fabrics made of cotton, rayon, etc., knitted fabrics, nonwoven fabrics, etc. However, in the present invention, when a polyester woven fabric is used among these various base sheets, a product with excellent adhesive strength to the printing ink adsorption layer formed later and excellent dimensional stability can be obtained. There are advantages.

The porous polyurethane layer constituting the adsorption layer of the printing sheet of the present invention has a thickness of about 3 μm to 30 μm and has a large number of continuous pores ranging from submicron to several microns in size, as described below. Depending on the polyurethane resin used and the method of forming the adsorption layer,
In addition to firmly adhering to the base sheet, the layer itself has excellent water resistance, wash resistance, flexibility, bending resistance, and ink adsorption and fixation properties.

Next, to explain the polyurethane emulsion used in the present invention and its method of use, which mainly characterizes the present invention, the polyurethane emulsion used in the present invention has a hydrophobic polyurethane resin (a) that has a high mutual solubility with water. It is an emulsion in which an appropriate amount of water is emulsified and dispersed in a polyurethane solution dissolved and/or dispersed in a limited organic solvent. The hydrophobic polyurethane (a) itself is a conceptually known material, and is obtained by reacting a hydrophobic polyol, an organic diisocyanate, and a chain extender. Examples of the hydrophobic polyol include , polyethylene adipate, polyethylene propylene adipate, polyethylene butylene adipate, polydielene adipate, polybutylene adipate, polyethylene succinate, polybutylene succinate, polyethylene sebacate, polybutylene seba organic diisocyanates include 4,4'-diphenylmethane diisocyanate (MDI), water-added
MDI, isophorone diisocyanate, 1,3-
xylylene diisocyanate, 1,4-xylylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate,
Examples include 1,5-naphthalene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, etc. Chain extenders include ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, 1,6
-hexanediol, ethylenediamine, 1,2
-propylene diamine, trimethylene diamine,
Examples include tetramethylene diamine, hexamethylene diamine, decamethylene diamine, isophorone diamine, m-xylylene diamine, hydrazine, water, and the like.

Any of the above-mentioned hydrophobic polyurethanes can be used in the present invention, and they are used by being dissolved and/or dispersed in the following organic solvents having a certain degree of mutual solubility with water.

The preferred organic solvent is 120℃ at normal pressure.
Those having the following boiling points, such as methyl ethyl ketone, methyl-n-propyl ketone, methyl isobutyl ketone, diethyl ketone, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, butyl acetate, etc. , cyclohexane, tetrahydrofuran, dioxane, methanol, ethanol, isopropyl alcohol, butanol, toluene, xylene,
dimethylformamide, dimethyl sulfoxide,
Perchlorethylene, trichlorethylene, methyl cellosolve, butyl cellosolve, cellosolve acetate, etc. can also be used. Among these organic solvents, organic solvents that have limited mutual solubility with water or those that do not dissolve at all are mixed with other solvents and used with limited mutual solubility with water. Of course, the above solvents can also be used as a mixed solvent.

The hydrophobic polyurethane resin is preferably dissolved and/or dispersed in the organic solvent in an amount such that the solid content thereof is about 5 to 60% by weight.

Particularly preferred solutions or dispersions of the hydrophobic polyurethane (a) in the present invention as described above are those that do not substantially dissolve the hydrophobic polyurethane (a);
A dispersion of hydrophobic polyurethane obtained by reacting the three components of the urethane raw materials in the organic solvent that has a limited mutual solubility with water and preferably has a boiling point of 120°C or less at normal pressure. The dispersion contains hydrophobic polyurethane from about 0.1 to
It has a size of 5μ and is uniformly and finely dispersed in an organic solvent, and has excellent dispersion stability when made into a water-in-oil emulsion, and as a result, the effects of the present invention are particularly remarkable. .

The polyurethane emulsion used in the present invention is prepared by stirring the above-mentioned mixed dispersion liquid vigorously and adding less than a saturated amount of water, for example, about 50 to 500 parts by weight per 100 parts by weight of solids in the mixed dispersion liquid. of water. When emulsifying this water, it is possible to use an appropriate amount of a conventionally known nonionic water-in-oil emulsifier; however, such conventionally known emulsifiers reduce the water resistance of the ink adsorption layer that is later formed to some extent. It should not be used in excessive amounts due to the possibility of According to detailed research conducted by the present inventors, when a specific hydrophilic polyurethane (b) is used as an emulsifier instead of such a conventionally used emulsifier, the water resistance, washing resistance, and It has been found that the emulsion can ensure long-term dispersion stability without impairing properties or other physical properties, and can therefore provide an adsorption layer with an excellent uniform, fine, and continuous pore structure. Such specific hydrophilic polyurethane (b) may contain about 20 to 40% by weight of polyoxyethylene groups based on the total weight of the polyurethane and be soluble in organic solvents.
Such polyurethane (b) is prepared in the same manner as the polyurethane (a) above, except that a part of the hydrophobic polyol is replaced with polyethylene glycol or its equivalent, and is prepared as a solution in an organic solvent. is preferred. Further, although the same effect can be achieved even if the polyurethane is produced by a method different from that of the polyurethane (a), the former method is economically advantageous.

The above polyurethane (b) is added to the polyurethane dispersion as a solution in an organic solvent or alone.
a:b=approximately 90~99:approximately 10~1 weight ratio (solid content)
It is preferable to mix with

The emulsion thus obtained is a milky white creamy fluid, and remains stable even if left as is for several months. Various additives such as colorants, crosslinking agents, stabilizers, fillers, and other known additives can be optionally added to such emulsions as necessary.

In the method of the present invention, the emulsion is applied to one or both surfaces of the base sheet, preferably a polyester woven fabric, to form an adsorption layer. Any known method such as coating method, dipping method, or combination method thereof may be used, and the amount of application and/or impregnation may vary widely depending on the purpose, such as about 5 to 2000 g (solid content)/ ^m2 . It can be changed.

The drying process in the method of the present invention can be completed in a very short time and without the need for any complicated treatment. hand,
Such short drying time is extremely advantageous compared to conventional methods. That is, the coated and/or impregnated substrate is dried at about 600-100°C for about 1-3 minutes to remove the organic solvent, and then dried at about 100-150°C.
The desired printing sheet of the present invention can be obtained by simply drying the sheet for about 1 to 3 minutes to remove moisture.
Such a short drying process is achieved because the hydrophobic polyurethane (a) used as a film forming agent in the present invention accounts for more than 90% by weight of the total polyurethane, and is composed of fine particles from beginning to end. This is thought to be due to the fact that it is stably dispersed and emulsified with water using a small amount of surfactant (polyurethane b), and when drying, it quickly and easily comes into contact with water due to evaporation of the organic solvent, causing gelation. It will be done.

The printing sheet obtained by the present invention as described above has a very fine pore structure and has excellent various physical properties, especially excellent printing ink adsorption and fixation properties, water resistance, and water resistance that cannot be achieved with conventional techniques. wash resistance,
It has flexibility and bending resistance, and is useful as various display labels and outdoor printing sheets. Furthermore, in the method of the present invention, the formation of the adsorption layer requires only the application and drying of an emulsion, which is extremely simplified and very economical compared to conventional methods. In addition, since the coating film is formed using a dry coagulation method, the problem of reduced adhesive strength caused by conventional wet coagulation is solved, and the polyester substrate, which had many problems with wet methods, can be used freely, resulting in excellent results. A printing sheet having excellent printability and dimensional stability is provided.

Next, the present invention will be specifically explained with reference to Examples, where all parts and percentages are based on weight.

First, hydrophobic polyurethane dispersions A, B, and hydrophilic polyurethane solution C were obtained as follows.

1. Production of hydrophobic polyurethane dispersion A 1000 parts of polytetramethylene glycol (average molecular weight approximately 1000, hydroxyl value 112), 93 parts ethylene glycol, and 625 g diphenylmethane diisocyanate were added to 1500 parts methyl ethyl ketone.
After reacting at 60° C. for 8 hours, 2500 parts of methyl ethyl ketone was added, and the mixture was cooled to room temperature with stirring to obtain a milky white hydrophobic polyurethane dispersion A with a solid content of 30%.

2 Production of hydrophobic polyurethane dispersion B 1,4-butane ethylene adipate (average molecular weight approximately 1000, hydroxyl value 112) 1000 parts, 1,4-
Butanediol 144 parts Methyl ethyl ketone 1144 parts
and diphenylmethane diisocyanate
After reacting 650 parts at 70° C. for 8 hours, 3042 parts of methyl ethyl ketone was further added to homogenize the mixture, and the mixture was cooled to room temperature with stirring to obtain a milky white hydrophobic polyurethane dispersion B with a solid content of 30%.

3 Production of hydrophilic polyurethane solution C Polypropylene glycol (average molecular weight approx.
After reacting 4000 parts of 2000 hydroxyl value 56) with 750 parts of diphenylmethane diisocyanate at 80°C for 3 hours, 2000 parts of methyl ethyl ketone was added to fully homogenize the reaction system. , hydroxyl value 112)
Add 2000 parts, react at 75℃ for 5 hours, and then
2500 parts of methyl ethyl ketone was added and stirred uniformly to obtain a hydrophilic polyurethane solution C having a solid content of 60% and a polyethylene glycol content of about 29.6%.

Hydrophobic polyurethane dispersions A, B and polyurethane solution C thus obtained, an organic solvent and water were stirred with a homomixer to prepare water-in-oil polyurethane emulsions D and E.

The compositions of the water-in-oil polyurethane emulsions D and E are as follows.

Composition of water-in-oil polyurethane emulsion D Hydrophobic polyurethane solution A 100 parts Hydrophilic polyurethane solution C 4 parts Methyl ethyl ketone 20 parts Toluene 20 parts Water 80 parts Composition of water-in-oil polyurethane emulsion E Hydrophobic polyurethane dispersion B 100 parts Hydrophilic polyurethane solution C 3 parts Methyl ethyl ketone 20 parts Xylene 20 parts Water 75 parts Example 1 100 parts by weight of water-in-oil polyurethane emulsion D was placed on one side of a polyester fiber taffeta of 75 denier warp and weft. A blended composition consisting of 18 parts by weight of MEK, 18 parts by weight of toluene, 2 parts by weight of an isocyanate-based crosslinking agent (manufactured by Dainichi Seikagyo Co., Ltd.) and 60 parts by weight of water was applied with a doctor knife to a wet weight of 35 g/ ^m2 . Then at 90℃
By heating and drying for 30 seconds at 120° C. for 1 minute, a printing sheet was obtained in which a porous layer with a surface opening diameter of about 1 to 8 microns was provided on the coated surface of polyester fiber taffeta.

This sheet has a soft texture that is almost the same as that of polyester fiber taffeta before coating, has strong adhesion between the porous layer and the taffeta base, and has good printability. Ta.

Example 2 Water-in-oil polyurethane emulsion E 100 parts by weight MEK 18 parts by weight Toluene 18 parts by weight Isocyanate crosslinking agent (Dainichiseika Kogyo Co., Ltd.) Co., Ltd.) 2 parts by weight Calcium carbonate powder 15 parts by weight Water 60 parts by weight A blended composition was applied to give a wet weight of 25 g/ ^m2 , and then heated at 90°C for 20 seconds and at 120°C for 1 hour.
The mixture was dried by heating for a minute to obtain a printing sheet. This printing sheet has a softer texture and drapability than the printing sheet obtained in Example 1, has strong adhesion between the porous layer and the taffeta substrate, and is suitable for printing. The printability was also good.

Claims (1)

[Scope of Claims] 1 Consists of a sheet-like substrate and a porous printing ink adsorption layer covering at least one surface of the substrate, the ink adsorption layer being a porous printing ink adsorption layer formed from a water-in-oil polyurethane emulsion. A printing sheet characterized by a polyurethane layer. 2. The printing sheet according to claim 1, wherein the sheet-like substrate is made of polyester fiber. 3. A patent claim characterized in that the water-in-oil polyurethane emulsion is a water-in-oil polyurethane emulsion obtained by emulsifying water in an organic solvent dispersion containing finely dispersed hydrophobic polyurethane. The printing sheet described in item 1 of the range. 4 Coating or impregnating at least one surface of the sheet-like substrate with a water-in-oil polyurethane emulsion, and removing an organic solvent from the coating layer or impregnated layer.
A method for producing a printing sheet having a porous printing ink adsorption layer on at least one surface of a sheet-like substrate, the method comprising the step of subsequently evaporating water. 5. The method for manufacturing a printing sheet according to claim 4, wherein the sheet-like substrate is made of polyester fiber. 6. A patent claim characterized in that the water-in-oil polyurethane emulsion is a water-in-oil polyurethane emulsion obtained by emulsifying water in an organic solvent dispersion containing finely dispersed hydrophobic polyurethane. A method for producing a printing sheet according to item 4.