JPS6358712B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of applying a polyurethane solution to the surface of a sheet material multiple times using a gravure roll, and particularly relates to a method of applying a polyurethane solution that does not cause interference color spots at that time. .

Conventionally, fiber aggregates such as woven fabrics, knitted fabrics, and nonwoven fabrics are impregnated with a solution or dispersion of polyurethane elastomer and coagulated into a porous sheet-like material, or the surface of the sheet-like material is coated with polyurethane elastomer or the like. BACKGROUND ART Sheet-like materials composed mainly of polymers and having a porous or non-porous layer formed thereon are manufactured and sold in large quantities today as artificial leather because their properties are similar to natural leather. Regarding the surface color of these artificial leathers,
In order to create a deep texture similar to natural leather, a method is generally used in which a polyurethane solution containing a dye is applied to the surface of artificial leather and dried, or a method in which an easy-to-dye polyurethane solution is applied, dried, and then dyed is used. It is being As a coating method at this time, a method using a gravure roll is usually used because it is suitable for mass production. However, with the method using a gravure roll, the amount of polyurethane solution that can be applied in one application is small, and in order to uniformly apply a predetermined amount of polyurethane solution, it is necessary to apply the polyurethane solution with a gravure roll, dry it, and then roll it again. Apply and dry polyurethane solution in layers,
Furthermore, so-called multi-stage coating, in which this operation is repeated multiple times, is performed. When such multi-stage coating is performed, the applied engraved pattern interferes with the engraved pattern applied above, resulting in interference color spots. Interference color spots are caused by the regular presence of thickness spots on the surface of a sheet-like material based on stamped patterns on polyurethane layers applied overlappingly with a gravure roll. At first glance, it can be seen that leather is an imitation that is far from natural leather, so in order to obtain high-quality artificial leather, multi-stage gravure coating that does not produce interference color spots must be performed. As a multi-stage gravure coating method that does not cause interference color spots, a method is known in which the engraved pattern is changed for each stage using a gravure roll with a different direction of engraving in each stage, but even if this method is used, interference color Preventing speckles is insufficient, and this method is not at all satisfactory, especially in fields such as surface coloring of artificial leather, where it is required that interference color speckles do not occur to a high degree. In particular, when applying a polyurethane solution that does not contain dyes or pigments in multiple stages using a gravure roll, the multi-stage gravure application is applied so that interference color spots occur only after subsequent embossing and subsequent dyeing. In other words, a long time has elapsed from the time multi-stage gravure coating is performed until the presence or absence of interference color spots can be discovered.
During this period, a large amount of products with interference color irregularities will be manufactured. It would be extremely useful if the presence or absence of interference color spots could be confirmed immediately during multi-stage gravure coating.

The present invention provides a multi-stage gravure coating method that is particularly useful in fields such as the field of artificial leather, which require a high degree of freedom from interference color spots. That is, in the present invention, when applying a polyurethane solution to the surface of a sheet-like material multiple times using a gravure roll, when the sheet-like material is separated from the surface of the gravure roll, the distance between the sheet-like material and the gravure roll is preferably 0.5 to 5.0 cm. 0.5~1.5cm
This multi-stage gravure coating method is characterized by selecting at least one of the following conditions: polyurethane type, solution viscosity, stamping mesh, and coating speed, which cause stringiness of the polyurethane solution, and applying polyurethane to the surface of a sheet-like material. By using such a method, it has become possible to significantly reduce interference color spots, and it has even become possible to completely eliminate interference color spots by selecting a specific polymer solution for gravure coating. In addition, stringing as used in the present invention refers to a phenomenon in which the polyurethane solution becomes thread-like and flows down between the gravure roll and the sheet-like material when the sheet-like material is separated from the surface of the gravure roll. Most of the thread-like polymer solution generated by the pulling phenomenon is 0.5-5.0
It is applied under conditions that cut in the cm range.

Incidentally, stringiness during application using a gravure roll can be observed by the method shown in FIG. In FIG. 1, 1 is an ink pan, 2 is a gravure roll, 3 is a doctor knife, 4 is a back roll, and 5 is a sheet material. The stringiness 6 can be observed by illuminating the separation point between the sheet material and the gravure roll with a light and viewing the separation point from the front, and the length thereof can also be easily measured. The direction of the dotted arrow in the figure is the method for observing stringiness.

When gravure applying a polymer solution to a sheet-like material, if the type of polymer, viscosity of the polymer solution, mesh diameter of the gravure roll stamp, and rotation speed of the gravure roll are set to specific conditions, the sheet-like material will be When the sheet material is separated from the gravure roll, threads of the polymer solution are generated between the sheet material and the gravure roll. Conventionally, when the threading phenomenon of the polymer solution occurs during gravure coating, the cut threads are Since objects fall onto the surface of the sheet-like material coated with gravure and stain the surface, gravure coating has been carried out under conditions that hardly cause stringing. In the case of multi-stage gravure coating, the stringing phenomenon, which was thought to be undesirable in conventional gravure coating methods, can be achieved by multi-stage gravure coating if the length of stringing is to be within a specific range. It has been found that interference color spots, which are the biggest drawback when using this method, almost no longer occur, and this is completely unexpected from conventional common sense.

There are no limitations on the sheet material to which the multi-stage gravure coating method of the present invention is applied, but as mentioned above, the coating method of the present invention is applicable to fields such as artificial leather where interference color spots are particularly required to be avoided. Therefore, polyurethane elastomer is contained in porous form inside the fiber aggregates such as sheet products, such as woven fabrics, knitted fabrics, and non-woven fabrics, which are manufactured in large quantities as artificial leather today. Suitable is a base layer having a polyurethane base layer, or a base layer having a coating layer formed of a porous or non-porous polyurethane elastomer formed on the surface of the base layer.

A method for obtaining such a sheet-like material is to impregnate a fiber aggregate, typically a nonwoven fabric, woven fabric, knitted fabric, or a laminated fabric of these, with a solution or dispersion of polyurethane elastomer, and then wet coagulation or dry coagulation. A method of obtaining a base layer by removing the solvent or dispersion medium and drying it, or applying a polyurethane elastomer solution or dispersion on this base layer and then wet coagulation or dry coagulation to form a porous or non-porous A method for forming a high-quality polyurethane coating layer, and a method for forming a polyurethane elastomer solution or dispersion with which the base layer is impregnated and a polyurethane elastomer solution or dispersion for the coating layer are coagulated simultaneously to form the base layer and the coating layer at once. Examples include how to obtain it.

Furthermore, the coating liquid used in the multi-stage gravure coating method of the present invention is a polyurethane solution, and in particular, a polyurethane solution using polycarbonate diol or a mixed polymer diol mainly composed of polycarbonate diol as a soft segment component can be used in the method of the present invention. It is preferable because it does not particularly cause interference color spots when
More preferably, a polycarbonate diol or a mixed diol mainly composed of polycarbonate diol is used as the soft segment component, an alicyclic diisocyanate is used as the diisocyanate component, an alicyclic diamine or a combination of this and hydrazine is used as a chain extender, or a ring diamine and an organic This is a solution of polyurethane synthesized from these in combination with acid dihydrazide. A dye is added to the polyurethane solution. If it is not added, or if it is necessary to color it in a darker color or another color depending on subsequent needs, the coating obtained by gravure coating should be dyed after gravure coating. A method of dyeing the membrane layer is used. When a dye is added to the polyurethane solution, the amount added is preferably in the range of 0.5 to 10.0% by weight based on the polyurethane.

Whether stringing of the polyurethane solution occurs during gravure coating, and the length of the stringing, depends primarily on the polyurethane polymer raw material, the viscosity of the polyurethane solution, and the diameter of the gravure roll's engraved mesh. In the present invention, stringing with a length of 0.5 to 5.0 cm is produced, which is determined by the rotation speed (surface speed) of the gravure roll. In order to produce stringing in this range, it is necessary to This can be achieved by selecting appropriate values for the viscosity of 100 to 200 centipoise, the diameter of the gravure engraving mesh to 140 to 200 centipoise, and the rotation speed of the gravure roll to 10 to 30 m/min. . Generally, in order to increase the length of stringing, increasing the viscosity of the polyurethane solution;
Either method may be used, such as reducing the diameter of the engraved mesh of the gravure roll or increasing the rotation speed of the gravure roll. In other words, the viscosity of the polyurethane solution, the diameter of the gravure imprint mesh,
By adjusting the rotational speed of the gravure roll, the stringing length can be set within the range of 0.5 to 5.0 cm, and by performing gravure coating under these conditions, multi-stage gravure coating can be performed with almost no interference color spots. It happens. If the stringing length is less than 0.5cm, interference color spots will become noticeable, and if it exceeds 5.0cm, the threads generated by stringing will scatter and adhere to the surface of the sheet-like material, significantly impairing the appearance. It will be a loss. In particular, by setting the string length in the range of 0.5 to 1.5 cm, it is possible to further suppress the occurrence of interference color spots and achieve beautiful coloring.

The present invention relates to a multi-stage gravure coating method, that is, a method in which a polyurethane solution is applied to the surface of a sheet-like material using a gravure roll, the solvent is removed and the polyurethane solution is dried, and then a polyurethane solution is further coated on top of the polyurethane solution using a gravure roll. However, the method of coating under stringy conditions of the present invention may be employed in all stages of a multi-stage gravure coating method, or may be employed in one of the stages, but preferably it is a method employed in all stages. be.

In the polyurethane solution applied in the present invention,
In addition to dyes, various stabilizers such as antioxidants, ultraviolet absorbers, and antistatic agents, fillers, and the like may be added. If no dye is added to the polyurethane solution, dyeing can be done by immersing the sheet-like material in the dye solution after multi-stage gravure coating, or by applying the dye solution onto the sheet-like material. used.

The present invention will be specifically explained below using examples.
Note that all percentages in this example are based on weight.

Example 1 Nitrogen content (weight ratio of nitrogen atoms based on the amount of raw material isocyanate in polyurethane) synthesized from polyhexamethylene adipate glycol, diphenylmethane-4,4'-diisocyanate, and ethylene glycol in a nonwoven fabric made of nylon fibers 3.8% polyurethane elastomer 14%, polyvinyl chloride 2.8%, stearyl alcohol 0.7% and dimethylformamide 82.5%
The same polymer solution was applied on top of this at a solid content of 60 g/ ^m2 , and then soaked in an aqueous solution at 40 °C containing 30% dimethylformamide for 30 g/m2.
After solidifying for a minute, the solvent was removed and dried to produce a sheet material. Next, on this sheet material, 6% polyurethane elastomer synthesized from polycarbonate glycol, isophorone diisocyanate and isophorone diamine, 1.2% Orazol Brown 2RL, and ethyl cellosolve were added.
42.8%, 38% isopropyl alcohol and 12% toluene (viscosity 150 centipoise)
was coated in three stages at a line speed of 15 m/min using a gravure roll with 150 mesh markings (coating amount: 1.8 g/m ² in terms of solid content). The stringiness during gravure application was 0.7 cm, and there was no interference pattern, and uniform application was possible. When this was further subjected to embossing with a rough texture pattern and fir processing, an artificial leather with a luxurious feel was obtained.

Comparative Examples 1 and 2 On the sheet-like material produced as in Example 1, 6% of the same polyurethane elastomer used for the sheet-like material, 1% of polyvinyl chloride, 2.1% of Orazol Brown 2RL, and dimethyl were added. 27% formamide, 35.5% acetone and cyclohexane
When a polymer solution containing 28.4% (viscosity: 150 centipoise) was gravure coated in the same manner as described above, there was almost no stringing during gravure coating and severe interference color spots occurred. Furthermore, this product was subjected to embossing and fir processing in the same manner as in Example 1, but the color spots were so noticeable that it lacked a luxurious feel.

On the other hand, on the sheet material produced as in Example 1, 8% polyurethane elastomer (Paraprene 26S) manufactured by Nippon Polyurethane Industries, 2.4% Orazol Brown 2RL, and dimethylformamide were placed.
26%, acetone 34% and cyclohexanone 29.6
% (viscosity: 150 centipoise) was gravure coated in the same manner as in Example 1, the stringiness during gravure coating was approximately 0.2 cm, and a fairly severe interference pattern was generated. Next, this was subjected to embossing and fir processing in the same manner as in Example 1, but the color spots were noticeable and the sense of luxury was low.

Example 2 Polycarbonate glycol, polyethylene glycol,
5% polyurethane elastomer synthesized from isophorone diisocyanate and dicyclohexylmethane-4,4'-diamine, ethyl cellosolve 43
%, isopropyl alcohol 37% and toluene 15%
% (viscosity 120 centipoise) in the same manner as in Example 1, stringing of 0.9 cm was observed during gravure coating. Next, this was embossed with a hard pattern, and then dyed using the Jitzger method under the following dyeing conditions: Dye type and concentration Lacol Brown 3R 3%
owf bath ratio 1:100 Dyeing temperature and time After dyeing at 60°C for 20 minutes, artificial leather was manufactured by soaping, washing, drying and fir processing. This product had no gravure interference pattern, was uniform in color, and had a very high quality feel.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the state of stringiness during gravure coating according to the present invention.

Claims (1)

[Claims] 1. When applying a polyurethane solution to the surface of a sheet-like material multiple times using a gravure roll, when the sheet-like material is separated from the surface of the gravure roll, the difference between the sheet-like material and the gravure roll is 0.5 to 1.
A multi-stage gravure coating method characterized by applying a polyurethane solution to the surface of a sheet-like material by selecting at least one of the following conditions: polyurethane type, solution viscosity, stamping mesh, and coating speed that cause stringing of a 5.0 cm long polyurethane solution. . 2. The multistage material according to claim 1, wherein the sheet-like material is a substrate in which a fiber aggregate contains a porous polyurethane elastomer, or a porous or non-porous polyurethane coating layer is formed on the surface of the substrate. Gravure coating method. 3. The multi-stage gravure coating method according to claim 1 or 2, wherein the polyurethane solution is a solution of a polyurethane elastomer synthesized using polycarbonate diol or a mixed polymer diol mainly composed of polycarbonate diol as a soft segment component.