JP2000250246A - Pressure sensitive adhesive sheet for wet electrophotographic printing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure good adhesion of a toner to a recording sheet, to attain good shift of the toner to the recording sheet, to prevent the contamination of a pressing rolls with the toner due to shift during passing through the rolls and to avoid illegibleness of information due to the transfer of the toner to other face when a pressure sensitive adhesive sheet is opened. SOLUTION: A layer of a pressure sensitive adhesive obtained by graft- polymerizing 5-20 wt.% methyl methacrylate on natural rubber is formed on both faces of a base sheet by 3-10 g/m2 per one face. In other way, a layer of a pressure sensitive adhesive obtained by graft-polymerizing 5-20 wt.% methyl methacrylate on natural rubber is formed on one face of a base sheet by 3-10 g/m2 and a layer of a polyethylene-base resin having a metallic ionic bond between polymer chains is formed on the other face. The former sheet is suitable for a pressure sensitive adhesive postcard folded in V shape and the latter sheet is suitable for a pressure sensitive adhesive postcard folded in Z shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-sensitive adhesive sheet which can be suitably used in a so-called "wet electrophotographic printing system" for printing using a liquid toner. More specifically, a foldable sheet or a superposed sheet having a facing surface which is temporarily adhered but can be easily peeled off as necessary, for example, a postcard having a confidentiality such as an information concealing sheet, a sealed letter, a notice, a card, a lottery The present invention relates to a pressure-sensitive adhesive sheet for wet electrophotographic printing which can be suitably used for a sheet for carrying information such as.

[0002]

2. Description of the Related Art Heretofore, as a method of copying a large amount of information such as characters and images, there have been printing methods such as offset printing and gravure printing. These conventional printing methods are characterized in that a printing plate is created by duplicating information, and ink is transferred from the printing plate to a recording sheet such as paper to copy information. Since the production of a printing plate is a laborious and time-consuming operation, the conventional printing method is a very excellent method for duplicating a large amount of the same information. This method is not suitable for copying in combination.

[0003] From such a background, an electronic printing method typified by a copying machine has become mainstream as a method for performing a small amount of copying. Since the electronic printing method does not require plate making work,
This method is suitable for small-volume duplication that conventional printing methods are not good at. As the electronic printing method, various methods such as a thermal recording method, an electrophotographic recording method, a thermal transfer recording method, and an ink jet recording method have been proposed, and a large number of copiers, printers, facsimile machines, and the like using these methods have been actually circulated. ing.

[0004] At present, in the case of copying text and simple illustration information, it is common to use a monochrome copier. However, in the case of printing full-color information, which has gradations such as photographs. In many cases, a conventional printing method was employed. This is because the electronic printing method is often inferior to the conventional printing method in terms of image quality, cost, speed, and the like.

[0005] Among the electroprinting methods, the dry electrophotographic method is as follows.
In a method typified by an office copying machine or the like, a solid powder toner composed of a pigment and a synthetic resin is used as a toner for forming an image. In the image forming method, recording (printing) is performed by a method in which toner of an electrostatic latent image generated by corona charging is adsorbed on a drum or the like, and the toner is heated and pressed onto a recording sheet to transfer the toner. This dry electrophotography method has the characteristic that the finer the toner, the higher the resolution, but this makes it easier for the toner to scatter around and causes health problems if inhaled. There is a limit to this, and it is difficult to obtain high resolution.
Further, when paper or the like is used as a recording sheet, the thickness tends to be non-uniform, the charge density on the recording sheet surface varies due to corona discharge, and curl occurs because the recording sheet must be melted and solidified at a somewhat high temperature. There are many problems.

The ink-jet method is a method of forming an image by ejecting fine ink droplets onto a recording sheet surface. However, since a water-soluble ink using a dye as a coloring material is used, weather resistance and water resistance are poor. In addition, there is a problem that a special paper having a high liquid absorbing capacity must be used. Further, it has been pointed out that the heat-sensitive recording method and the thermal transfer recording method require the use of a special recording sheet, resulting in an increase in cost.

In view of the circumstances described above, when satisfying conditions such as high image quality, high speed, and low cost, it is said that a wet electrophotographic method is the most promising among various electronic printing methods. The wet electrophotographic method has advantages in that the toner can be made finer and the pigment can be used as a coloring material as compared with the dry electrophotographic method, so that there is no problem of weather resistance and water resistance.

On the other hand, with the amendment of the Postal Law, what are called "pressure-sensitive adhesive postcards" and "pressure-sensitive adhesive envelopes" are being used in various fields for the purpose of reducing mailing costs and securing confidentiality. As an example of this configuration, using a sheet coated with a re-peelable pressure-sensitive adhesive that can be adhered to a base sheet by pressure, printing confidential information, folding the sheet in a V-fold or Z-fold, and passing it between pressure rolls Information to be hidden and recorded (printed)
There is a method of manufacturing a postcard or a postcard by bonding the surfaces (confidential surfaces) that have been made. After receiving the postcard or letter, the recipient peels off the adhered confidential surface and reads the information. After peeling, it is designed so that it cannot be re-adhered by a normal method, and a function (confidentiality) that can determine whether or not it has been opened during mailing is secured.

Various methods have been proposed for this pressure-sensitive adhesive sheet. For example, JP-A-4-59395 discloses an adhesive composition comprising a non-peelable adhesive base and a fine-grained filler exhibiting no affinity for the adhesive base on at least a part of the base sheet surface. There is a proposal for an information carrier sheet characterized by providing the above layer. In this proposal, an average particle diameter of 10 μm to 30 μm, preferably 1 to 20 μm, a fine particulate filler comprising a combination of silica and other fillers, 100 to 400 parts by weight per 100 parts by weight of the pressure-sensitive adhesive,
Preferably 130-300, more preferably 150-2
By adding 50 parts by weight, the blocking resistance is improved, and the silicone oil used at the time of electrostatic recording is absorbed to prevent a decrease in adhesive strength.

Japanese Patent Application Laid-Open No. Hei 7-18232 discloses that at least a part of a support sheet is provided with a pressure-sensitive adhesive made of latex and two or more kinds of non-affinity adhesives for the pressure-sensitive adhesive. There has been proposed an information carrier sheet provided with a layer of a pseudo-adhesive composed of a fine-particle filler and a modified polyvinyl alcohol having an affinity for both the pressure-sensitive adhesive and the fine-particle filler. These pressure-sensitive adhesive papers have been developed for dry electrophotographic printers. At present, a sheet to which a pressure-sensitive adhesive has been applied is processed into a form after offset UV printing of fixed text, ruled lines, and the like on a business form printing machine. The processed form is printed with personal information and the like using a dry electrophotographic printer.

[0011]

The digital printing method using the wet electrophotographic method is a new printing machine having excellent advantages, but in order to maximize its characteristics, it is necessary to use a digital printing method.
Special performance is required for the recording sheet used. That is, the recording sheet has a good adhesion between the toner and the recording sheet, a good transfer of the toner to the recording sheet,
Even when the toner is transferred, the toner is transferred to the pressure roll when passing through the pressure roll and does not contaminate the pressure roll, and when the pressure-sensitive adhesive sheet is opened, the toner is transferred to another surface so that the information can be read. Performance such as not becoming difficult is required.

An object of the present invention is to develop a pressure-sensitive adhesive sheet for wet electrophotographic printing satisfying these required properties.

[0013]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, as a pressure-sensitive adhesive used for a pressure-sensitive adhesive sheet, 5 to 20% by weight of methyl methacrylate with respect to natural rubber. It has been found that an adhesive having% graft polymerization is most effective in solving the problems of the present invention, and the present invention has been completed. That is, the first invention of the present invention provides a base sheet on both sides with a natural rubber
A pressure-sensitive adhesive sheet for wet electrophotographic printing, characterized in that a pressure-sensitive adhesive layer obtained by graft polymerization of 20% by weight of methyl methacrylate is formed at 3 to 10 g / m ^{2 on} one side.

According to a second aspect of the present invention, there is provided a pressure-sensitive adhesive layer obtained by graft-polymerizing 5 to 20% by weight of methyl methacrylate with respect to a natural rubber on one surface of a base sheet. ^{(2) A} pressure-sensitive adhesive sheet for wet electrophotographic printing, wherein a resin layer having polyethylene ion as a main component and having a metal ion bond between polymer chains is formed on the other surface.

[0015]

Next, the present invention will be described in detail. The base sheet of the present invention is paper, synthetic paper, synthetic resin film,
Use a sheet material such as a nonwoven fabric. As the paper, usually softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP), softwood bleached sulphite pulp (N
BSP) and other papermaking pulp in 300 to 600 ml C.I.
S. F. Filler such as clay, kaolin, calcium carbonate, titanium dioxide, etc., paper strength enhancer such as starch, PVA, polyacrylamide, wet paper strength such as melamine resin, urea resin, polyamide / epichlorohydrin, polyacrylamide A sizing agent such as an enhancer, a rosin-based sizing agent, an alkyl ketene dimer-based sizing agent, a fluorescent whitening agent, a coloring dye / pigment, a fixing agent, etc. are appropriately added, and known papermaking such as a round paper machine or a fourdrinier paper machine. Using the machine in accordance with the usual law,
The paper in the normal 40~150g / m ^2. It is to be noted that a sizing agent, a paper strength enhancer, or the like can be appropriately applied by a size press device or the like during papermaking. In addition, a coating layer or the like made of a filler and a binder for improving smoothness may be provided on the surface of the coating within a range not to impair the object of the present invention.

The natural rubber-based pressure-sensitive adhesive used in the present invention can be obtained by polymerizing natural rubber with methyl titacrylate using a well-known method. When the amount is less than 5% by weight, the transfer and fixing of the toner is not sufficient, and when the amount exceeds 20% by weight, the adhesive force of the natural rubber is remarkably reduced, so that it cannot be used as a pressure-sensitive adhesive paper. It is necessary to graft polymerize methacrylate by 5 to 20% by weight. The amount of the pressure-sensitive adhesive applied is 3 g / m
The adhesive force is insufficient is less than ^2, because the adhesive force and Kosu a 10g / m ² can not be peeled off too strong, it is necessary to a base sheet per side 3~10g / m ^2, the air in this application Known coating methods such as a knife coater, a gravure coater, a blade coater, a roll coater, and a bar coater are used.

In the present invention, additives can be added to the pressure-sensitive adhesive within a range not to impair the object of the present invention. For example, kaolin, talc, calcium carbonate, silica,
Aluminum hydroxide, plastic pigment and the like, and cereal starch particles such as flour and the like can be used. These adhesives and fillers, cereal starch particles and the like and antioxidants, additives such as ultraviolet absorbers are appropriately combined, and no blocking occurs during storage of the paper by a known method, and the pressure-sensitive adhesive strength is good.
After pressure-sensitive bonding, it can be peeled off with a moderate force to read confidential information, and has a performance that cannot be re-bonded by a normal method.

The pressure-sensitive adhesive sheet for wet electrophotographic printing of the present invention can be used for various applications as described below.
Hereinafter, V-folded and Z-folded pressure-sensitive adhesive postcards will be described as examples. FIG. 1 is an explanatory diagram of a state where the V-fold is folded,
FIG. 4 is an explanatory diagram of a state where the Z-fold is folded.

In the case of a multi-fold type such as Z-fold and W-fold, it is necessary to provide the pressure-sensitive adhesive layer on both sides of the base sheet. In the case of the V-fold type, the pressure-sensitive adhesive is applied to only one side. Is applied. In this case, the surface to which the pressure-sensitive adhesive is not applied does not have good transfer adhesion of the toner, and the toner tends to be peeled off by the pressure roll.

As a result of various studies by the present inventors, it has been found that this problem can be solved by using a certain special resin. That is, on the surface opposite to the surface on which the pressure-sensitive adhesive is applied, a resin containing polyethylene as a main component and having a metal ion bond between polymer chains (hereinafter, “polyethylene ionomer resin”)
It is found that the above-mentioned problem can be solved by using the above-mentioned method.

The polyethylene ionomer resin only needs to be present on the surface on which the pressure-sensitive adhesive is not applied, and the processing form is not limited. For example, only a polyethylene ionomer resin may be applied to the surface of the sheet substrate, or
It may be mixed with other substances and applied. When the polyethylene ionomer resin is applied to the surface of the base sheet, the effect is exhibited with a solid content of only 0.01 g / m ^2. It can be seen that it is sufficient if it exists on the sheet substrate surface in the amount of (1).

[0022]

On both sides of high-quality paper of EXAMPLE 1 basis weight 80 g / m ^2, natural rubber latex obtained by polymerizing 15 wt% graft to the natural rubber methyl methacrylate (trade name "QY-04", Quartey-
Synthetic silica having an average particle size of 1.8 μm (trade name “Sylysia 35
0 ", manufactured by Fuji Silysia K.K.) and 50 parts by weight of wheat starch having an average particle size of 17 μm were added to the surface of the coating solution using an air knife coater to give 5 g /
m ² , 8 g / m ² were applied to both sides of the back surface to prepare a Z-fold pressure-sensitive adhesive paper.

Example 2 A pressure-sensitive adhesive paper was produced in the same manner as in Example 1, except that the graft polymerization rate of methyl methacrylate of the natural rubber latex as the adhesive was changed to 5% by weight.

Example 3 A pressure-sensitive adhesive paper was produced in the same manner as in Example 1, except that silica in the adhesive in Example 1 was changed to light calcium carbonate.

Example 4 An aqueous dispersion of a polyethylene ionomer resin (manufactured by Mitsui Chemicals, Inc.) on one surface of a high-quality paper having a basis weight of 140 g / m ² and the same adhesive as in Example 1 on one surface and 5 g / m ^{2 on} the other surface 0.05 g /
m ² was applied with an air knife coater to prepare a V-fold pressure-sensitive adhesive paper.

Comparative Example 1 A pressure-sensitive adhesive paper was prepared in the same manner as in Example 1 except that the graft polymerization rate of methyl methacrylate of the natural rubber latex as the adhesive was changed to 25% by weight.

Comparative Example 2 A pressure-sensitive adhesive paper was produced in the same manner as in Example 1 except that the natural rubber latex as the adhesive in Example 1 was changed to a material not subjected to methyl methacrylate graft polymerization.

Comparative Example 3 A pressure-sensitive adhesive paper was produced in the same manner as in Example 4 except that the aqueous dispersion of the polyethylene ionomer resin in Example 4 was not applied.

The samples of the pressure-sensitive adhesive sheets for wet electrophotographic printing obtained in the above Examples and Comparative Examples were evaluated for the transfer fixing property and the practical performance of the pressure-sensitive adhesive paper according to the evaluation methods described below. Was. The evaluation methods are evaluation of transfer fixing property by a sensitivity test and evaluation of practical performance of pressure-sensitive adhesive paper. Specifically, a wet electrophotographic printing machine (trade name “E-PRIN”
T ", manufactured by INDIGO Co., Ltd.), and the printed matter was used for evaluation. The transfer and fixability evaluation was conducted by four tests of a transfer test, a cellophane tape peeling test, an eraser rubbing test, and a nail scratching test.
It is the total score evaluated on a perfect score. The practical performance of the pressure-sensitive adhesive paper was evaluated based on the adhesive strength, the transfer of the toner to the other surface during peeling, and the contamination of the pressure roll.

Hereinafter, the evaluation of the transfer fixing property will be described in detail. The “transfer test” is a test in which four toners of cyan, magenta, yellow, and black are solid-printed respectively, and after printing, it is visually checked whether the toner is correctly transferred to a recording sheet. It was as follows. 4 points: A state in which all four colors are printed finely. 3 points: A state in which the area of the poor transfer portion is 5% or less with respect to the total print area. 2 points: The area of the poor transfer portion is 5% with respect to the total print area. Larger, 10% or less state 1 point: The area of the poor transfer part is more than 10% and less than 15% with respect to the whole print area. 0 point: The area of the poor transfer part is 15 with respect to the whole print area. % Or more

"Cellophane tape peeling test" refers to
Adhesive tape made of cellophane (trade name "Cellotape", manufactured by Nichiban Co., Ltd.) is reciprocally attached to the solid printed portion of the color by one reciprocation of a 5 kg rubber roll, and the degree of peeling of the toner when peeled after one hour is visually determined. The evaluation method was as follows. 4 points: A state in which the toner is not peeled off from the printing surface in all four colors. 3 points: A state in which the peeled area is 5% or more with respect to the entire printed area. 2 points: A peeled area is larger than 5% with respect to the entire printed area.
State where the area is 10% or less 1 point: State where the peeled area is larger than 10% and smaller than 15% with respect to the entire printed area 0 point: State where the area of the defective transfer portion is 15% or more with respect to the entire printed area

"Eraser rubbing test" refers to the degree to which the toner on the printed surface is erased when the printed surface is rubbed five times with a plastic eraser (trade name "MONO", manufactured by Dragonfly Pencil Co., Ltd.). It is a test method to judge, and each evaluation point was as follows. 4 points: a state in which all four colors cannot be erased 3 points: a state in which the erase area is 5% or less of the entire print area 2 points: an erase area is greater than 5% with respect to the entire print area
State of 10% or less 1 point: State in which the peeled area is larger than 10% and smaller than 15% with respect to the entire printed area 0 point: State in which the area of the poor transfer portion is 15% or more with respect to the entire printed area

The "nail scratch test" is a test for visually judging the degree of scratching when the printed surface is scratched once with a nail. The evaluation points are as follows. A state in which all four colors of toner are not removed even if four points are scratched. Three points: A state in which one of four colors is taken. Two points: A state in which two of four colors are taken. One point: Among four colors. , 3 colors are taken 0 points: 4 colors are taken out of 4 colors

The scores of the above four tests are summed up to a maximum of 16
The points scored with a minimum of 0 points are the evaluation of transfer fixability by a sensitivity test. The act of sticking a cellophane adhesive tape, rubbing with nails, erasing with an eraser, etc. is the external force that the printed matter will actually receive This is suitable for judging whether the transfer fixability of the toner is practical or not. That is, when the above evaluation is 16 points, the transfer fixability is perfect. In addition, when the same test is performed on a printed material subjected to offset printing, the above evaluation is 12 to 14 points.
Those having 12 to 14 points can be said to have the same fixability as ordinary printed matter. When the score is 8 to 11, the transferability is almost perfect, but the fixability is slightly inferior to that of offset printing. When the above evaluation is 7 points or less, the transferability is poor, so that the minimum level of information copying is not satisfied, which is not suitable for practical use.

Next, evaluation of the practical performance of the pressure-sensitive adhesive paper will be described. The adhesive strength test is performed by V-folding or Z-folding the printed sample, pressure-sensitively bonding with a sealer (trade name "DS-6860", manufactured by Toppan Forms Co., Ltd.), and then measuring the 180-degree peel strength with a Tensilon universal tensile tester. It was measured (pulling speed was 300 mm / min). In the present invention, the adhesive strength is 4
It needs to be 0 to 100 g / 25 mm.

If the adhesive strength is lower than 40 g / 25 mm, the paper will open before it reaches the delivery destination. If the adhesive strength is higher than 100 g / 25 mm, the paper will be broken and the information will not be readable even if it is peeled. Each evaluation was as follows. ：: Adhesion force in the range of 40 g to 100 g / 25 mm Δ: Adhesion force of 10 g or more and less than 40 g, or 100 g or more and less than 150 g ×: Adhesion force of less than 10 g or 150 g or more

In the test of the transfer of the toner to the other surface at the time of peeling, the film was peeled after pressure-sensitive adhesion to an appropriate adhesive strength with a sealer, and the transfer of the toner to the other surface was visually judged. Each evaluation was as follows. ：: No image transfer at all Δ: State where the area of the transfer portion is less than 10% of the total print area X: State where the area of the transfer portion is 10% or more of the total print area

In the test for dirt on the pressure roll, the toner adhered to the pressure-sensitive adhesive roll when a certain number of sheets passed through the sealer was visually observed. Each evaluation was as follows. ：: no stain after passing 500 sheets Δ: stain when 100 to 500 sheets are passed ×: stain when less than 100 sheets

If all of the above evaluations are ○, this is a level that does not pose any practical problems as pressure-sensitive adhesive paper.

Table 1 shows the results of evaluation of transfer fixing properties of Examples 1 to 5 and Comparative Examples 1 and 2 by the above-mentioned sensitivity test.

[0041]

[Table 1]

Table 2 shows the evaluation results of the practical performance of the pressure-sensitive adhesive paper by the above-mentioned sensitivity tests of Examples 1 to 5 and Comparative Examples 1 and 2.

[0043]

[Table 2]

As is clear from the results in Tables 1 and 2, the pressure-sensitive adhesive papers obtained in the examples are excellent in wet electrophotographic printing suitability and also excellent in transfer fixability of toner. It can also be used as pressure-sensitive adhesive paper without any practical problems. On the other hand, it can be seen that the pressure-sensitive adhesive recording paper of the comparative example cannot achieve both wet electrophotographic aptitude and practically necessary performance as pressure-sensitive adhesive paper.

[0045]

The pressure-sensitive adhesive sheet for wet electrophotographic printing of the present invention can perform good printing by a wet electrophotographic method, has excellent toner transfer and fixation, and can be peeled off even after pressure-sensitive bonding. There is no toner transfer when reading the concealment information, and there is no roll contamination of the sealer during pressure-sensitive bonding, so that an appropriate adhesive force can be obtained. Utilizing such characteristics, the pressure-sensitive adhesive sheet of the present invention can be used for notification work such as postcards and sealed letters, confidential documents,
It can be used in a wide range of business as a pressure sensitive adhesive sheet for wet electrophotography in various lotteries, greeting cards, etc.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a state where a V-fold is folded.

FIG. 2 is a schematic surface development view of a V-fold.

FIG. 3 is a schematic rear view of a V-fold.

FIG. 4 is an explanatory diagram of a state where a Z-fold is folded.

FIG. 5 is a schematic surface development view of a Z-fold.

FIG. 6 is a schematic rear view development of the Z-fold.

[Explanation of symbols]

 1 destination information 2 concealment information 3 folding line

Claims (2)

[Claims] 1. A pressure-sensitive adhesive layer obtained by graft polymerization of 5 to 20% by weight of methyl methacrylate with respect to a natural rubber is formed on both sides of a base sheet at a rate of 3 to 10 g / m ² per one side. Pressure-sensitive adhesive sheet for wet electrophotographic printing. 2. A pressure-sensitive adhesive layer obtained by graft-polymerizing 5 to 20% by weight of methyl methacrylate with respect to natural rubber is formed on one surface of the base sheet at 3 to 10 g / m ² ,
A pressure-sensitive adhesive sheet for wet electrophotographic printing, wherein a resin layer containing polyethylene as a main component and having a metal ion bond between polymer chains is formed on another surface.