JP2005088278A - Laminated water-resistant paper suitable for recording due to electrophotographic system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide laminated water-resistant paper suitable for recording due to an electrophotographic system prevented from curling while using laminated paper wherein a thermoplastic resin is laminated on both surfaces of a paper base material. <P>SOLUTION: In the laminated water-resistant pepr wherein at least one layer comprising a thermoplastic resin is laminated on each of both surfaces of the paper base material, the heat shrinkage stress of the resin layer laminated on a printing surface side of the paper base material is made lower than that of the resin layer laminated on the back thereof. Concretely, the thickness of the resin layer is made thinner than that of the resin layer on the back side opposed to the printing surface side of the paper base material and the strain caused in a paper passing route after toner is fixed at the time of LBP printing is absorbed by the difference between the heat shrinkage stresses (forces ready to shrink at the time of heating) of the resin layers laminated on the upper and under surfaces of the paper base material to prevent the occurrence of curling. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a laminated water-resistant paper suitable for electrophotographic recording, in which layers made of a thermoplastic resin are laminated on both sides of a paper substrate.

  At present, recording by an electrophotographic method is generally performed. This method copies characters, images, etc. of a copy onto a recording sheet by transferring charged latent image toner. Plain paper copy machines (PPC machines), laser beam printers (LBP), etc. Used as a recording device.

  For such an electrophotographic recording sheet, paper is usually used, but when water resistance is required, so-called synthetic paper or laminated paper is used. Among these, the laminated paper is obtained by laminating a thermoplastic resin on a paper base. For example, as described in Patent Document 1, an extrusion lamination method or a co-extrusion lamination is performed on one or both sides of a paper base. It is manufactured by laminating a thermoplastic resin by the method. Patent Document 2 describes an electrophotographic transfer sheet in which the thermal shrinkage after heat treatment at 120 ° C. for 30 minutes of the resin film forming the thermoplastic resin film layer is 5% or less.

Japanese Patent No. 2763011 (Claim 1) JP 2002-258509 A (Claim 1)

  In the electrophotographic method, the latent image toner is transferred to a recording sheet and fixed by thermal fusion. Generally, the recording sheet is passed between hot rolls at about 200 ° C. At that time, in the case of laminated paper or the like, the resin on the surface is softened by heat, and the sheet passes through a complicated paper passage route bent in this softened state. At this time, the paper base in the laminated paper is curled due to forced bending, and the softened resin follows the curled shape of the base paper. End up. Usually, the sheet passing path is bent toward the print surface side, which causes a problem of curling on the print surface side.

  In addition, one of the main uses of electrophotographic recording sheets having water resistance is advertising media for display shelves of goods at convenience stores and supermarkets (commonly known as POP: Point Of Purchase). Above all, beauty is regarded as important. However, when printing or printing is performed by using an electrophotographic method using laminated paper, curling occurs, and the beauty and printed information may be difficult to see, and visibility may be impaired.

  In light of the above, the present invention has an object to provide a laminated water-resistant paper that does not cause curling during recording by an electrophotographic method while using a laminated paper in which a thermoplastic resin is laminated on both sides of a paper substrate. It is.

  As a result of intensive studies, the inventors of the present invention laminated the heat shrinkage stress (force to shrink when heated) of the resin layer laminated on the printing surface side on the back surface among the resin layers laminated on both sides of the paper substrate. The present invention has been completed by finding that the above-described problems can be solved by making the resin layer smaller than the resin layer. That is, the curling of the base paper that occurs through the paper passing path bent after heating is compensated by using the heat shrinkage stress of the resin layers laminated on the front and back sides.

That is, the present invention relates to a laminated water-resistant paper in which one or more layers made of a thermoplastic resin are laminated on both sides of a paper substrate, and a resin in which the heat shrinkage stress of the resin layer laminated on the printing surface side is laminated on the back surface. The present invention relates to a laminated water resistant paper characterized by being smaller than the heat shrinkage stress of the layer.
In particular, since the resin layer laminated on the printing surface side is thinner than the resin layer laminated on the back surface, the above problem can be achieved efficiently.

According to the present invention, it is possible to obtain a laminated water-resistant paper which is a laminated water-resistant paper in which a thermoplastic resin is laminated on both sides of a paper base material, and does not cause curling when printing by an electrophotographic method.
Therefore, according to the present invention, it is possible to obtain a water-resistant recording paper that is suitable for recording by an electrophotographic method and that provides a beautiful printed surface.

The present invention will be described in detail below.
In the present invention, the paper base refers to a product produced by intertwining and sticking plant fibers or plant fibers and other fibers. Any paper substrate such as this can be used in the present invention. However, when giving high gloss to the finished laminated water-resistant paper, the paper substrate is as smooth as possible, for example, high-quality paper. The use of coated paper or the like is preferred.

  The laminated water-resistant paper of the present invention is obtained by laminating one or more layers made of a thermoplastic resin on both sides of the paper substrate. In the present invention, it is important that the heat shrinkage stress of the resin layer laminated on the printing surface side is smaller than the heat shrinkage stress of the resin layer laminated on the back surface. The larger one compensates for the curl generated with the printing surface on the inside.

  As for the thickness of the resin layer to be laminated, the difference in the heat shrinkage stress between the front and back surfaces can be effectively obtained because the resin layer on the printing surface side is thinner than the resin layer on the back surface side. In particular, it is desirable that the resin layer on the printing surface side be 5 μm or thinner than the resin layer on the back surface side. When the difference in thickness is too small, the difference in heat shrinkage stress becomes small and the effect of compensation becomes low. However, if the thickness difference is too large, that is, if the back side is thicker and the heat shrinkage stress is too strong, it is considered that reverse curling to the back side will occur, so it is important to make the difference appropriate.

  Moreover, it is preferable that the thickness of all the resin layers laminated | stacked on the printing surface side shall be 5 micrometers or more, and the thickness of all the resin laminated | stacked on the back side shall be 10 micrometers or more. More preferably, the printing surface side is 10 to 15 μm and the back surface side is 15 to 25 μm. By making the thickness, the adhesion to the paper base material is further improved, and the occurrence of blisters is better suppressed. Can do.

  As the resin, any thermoplastic resin can be used as long as it is generally processable by an extrusion lamination method, and examples thereof include a homopolymer or a copolymer of a polyolefin resin such as polypropylene.

  In the outermost layer of the laminated water-resistant paper of the present invention, inorganic fillers such as titanium oxide and calcium carbonate can be blended for the purpose of imparting opacity, writing property and the like. However, since the compounding of the inorganic filler also causes the surface properties of the laminated water-resistant paper to deteriorate, the compounding amount should be 25% by weight or less, preferably 15% by weight or less, based on the outermost layer in which it is blended. preferable.

  In addition, when using laminated water-resistant paper for electrophotographic recording, it is particularly necessary to prevent charging. For this reason, also in the laminated water-resistant paper of the present invention, it is preferable to add or apply a known antistatic agent to at least the outermost resin layer. As the antistatic agent, an organic electrolyte such as an anionic, cationic or nonionic surfactant can be used. As a coating method of the antistatic agent, any of known coating methods can be employed.

  In the laminated water resistant paper of the present invention, various additives may be added to the paper base material and the thermoplastic resin layer, as long as the purpose of the present invention is not impaired, or a coating agent may be applied to the paper base material and the thermoplastic resin layer. Can be. For example, as these additives and coating agents, sizing agents and inorganic fillers (titanium oxide, calcium carbonate, clay, talc, silica, etc.) are used for paper bases, and blocking agents (acrylic beads) are used for thermoplastic resin layers. Commonly used additives and coating agents such as glass beads, silica, etc.) and adhesion improvers can be used.

  The laminated water-resistant paper of the present invention can be produced by laminating a thermoplastic resin layer on a paper base material by a known method such as an extrusion lamination method or a coextrusion lamination method alone or in combination as appropriate. As described above, when an inorganic filler such as titanium oxide is blended with the resin forming the outermost layer for the purpose of opaqueness, the lamination processability deteriorates, but in such a case, the resin blended with this inorganic filler is used. If coextrusion laminating with a resin not containing an inorganic filler, even if the thickness of the resin layer is reduced, troubles such as so-called film breakage can be suppressed and stable lamination can be performed.

  In addition, when a highly glossy surface condition is required for the laminated water-resistant paper of the present invention, in the case of extrusion lamination or coextrusion lamination, a cooling roll in contact with the molten resin is used with a mirror-finished peripheral surface, Furthermore, if the nip roll facing the cooling roll has a high hardness and the resin and the paper substrate are pressed and pressed with a high linear pressure, the laminated resin surface can be made highly glossy. For this purpose, it is preferable to use a nip roll having a hardness of 80 degrees (JIS K-6253) or more, and press and pressure bonding with a linear pressure of 15 kgf / cm or more. Here, the high gloss means that the gloss is 75% or more when measured according to JIS P-8142.

(Function)
The inventors of the present application have found that when the laminated water-resistant paper in which the thermoplastic resin is laminated on both sides of the paper substrate is used for recording by a PPC machine or LBP, the heated laminated water-resistant paper is bent. It was noticed that it was caused by the distortion caused at that time because it passed through the paper path, and it occurred when the heated and softened resin layer followed the shape of the curled base paper and the temperature decreased and fixed.

  The laminated water-resistant paper of the present invention solves this problem by absorbing the strain generated in the paper passing path by making a difference in the heat shrinkage stress (force to shrink by heating) of the resin layers laminated on the front and back sides. In particular, in the present invention, it is effective to make the printing surface side thinner than the back surface side with respect to the thickness of the resin layer laminated on both surfaces of the paper substrate. In general, when the recording sheet is paper, curl is less likely to occur as the thickness increases. However, since the present invention is a resin layer, the heat shrinkage stress increases as the amount of resin to be contracted increases, that is, as the thickness increases. It is considered that the curling on the print side can be compensated by the shrinking action of the resin layer on the back side.

  Usually, changing the physical properties of the front and back of the laminated paper is difficult to consider from the aspects of quality performance, handling, and operability, but the present invention focuses on the difference in physical properties and uses this on the contrary, It has achieved the challenge.

Below, this invention is demonstrated based on an Example.
In the examples and comparative examples, the evaluation of curling was performed as follows.

<Evaluation of curling>
After printing 100 sheets of A4 size sample using Fuji Xerox color laser beam printer Docu Print C3530, place the print sample on a flat desk and measure the curl height at the four corners. I took the value.

[Example 1]
A linear low density polyethylene (hereinafter referred to as SS-LLDPE) synthesized from a melted homopolypropylene (MFR 23 g / 10 min, density 0.91 g / cm ³ ) added with and mixed with 15% by weight of titanium oxide using a single-side catalyst. Extruded with T-die so that SS-LLDPE is located on both sides of high-quality paper on a high-quality paper with a basis weight of 157 g / m ² together with a melt of “Harmolex NH725N” manufactured by Nippon Polyolefin Co., Ltd. Co-extruded at a temperature of 300 ° C, and these molten resins and high-quality paper are pressed and pressure-bonded at a linear pressure of 15 kgf / cm using a mat-finished cooling roll and a nip roll with a hardness of 95 degrees to produce a laminated waterproof paper. did. At this time, the SS-LLDPE layer and the homopolypropylene layer thickness of the laminated water-resistant paper were both 5 μm on the printing surface side and 10 μm on the back surface side. That is, this laminated water-resistant paper is composed of titanium oxide-added homopolypropylene layer (5 μm) / titanium oxide-free SS-LLDPE layer (5 μm) / quality paper / titanium oxide-free SS-LLDPE layer (10 μm) / titanium oxide-added homopolypropylene. It has a laminated structure called a layer (10 μm).
After applying a cationic surfactant as an antistatic agent to the outermost layer on both sides of the laminated water-resistant paper obtained with a gravure coater at a coating amount of 0.1 g / m ² , the occurrence of curling was evaluated. .
The results are shown in Table 1. As is clear from Table 1, no curling was observed.

[Comparative Example 1]
A laminated waterproof paper was produced in the same manner as in Example 1 except that the thickness of the SS-LLDPE layer and the homopolypropylene layer laminated on both surfaces of the fine paper were both 10 μm. That is, this laminated water-resistant paper is composed of a titanium oxide-added homopolypropylene layer (10 μm) / titanium oxide-free SS-LLDPE layer (10 μm) / quality paper / titanium oxide-free SS-LLDPE layer (10 μm) / titanium oxide-added homopolypropylene. It has a laminated structure called a layer (10 μm).
After applying a cationic surfactant as an antistatic agent to the outermost layers on both sides of the laminated water-resistant paper obtained with a gravure coater at a coating amount of 0.1 g / m ² , the occurrence of curling was evaluated. .
The results are shown in Table 2. As is clear from Table 2, the laminated water-resistant paper obtained here was curled after LBP printing.

[Comparative Example 2]
A laminated water-resistant paper was produced in the same manner as in Example 1 except that the thickness of the SS-LLDPE layer and the homopolypropylene layer laminated on both sides of the fine paper were 10 μm on the print side and 5 μm on the back side. That is, this laminated water-resistant paper is composed of titanium oxide-added homopolypropylene layer (10 μm) / titanium oxide-free SS-LLDPE layer (10 μm) / quality paper / titanium oxide-free SS-LLDPE layer (5 μm) / titanium oxide-added homopolypropylene. It has a laminated structure called a layer (5 μm).
After applying a cationic surfactant as an antistatic agent to the outermost layers on both sides of the laminated water-resistant paper obtained with a gravure coater at a coating amount of 0.1 g / m ² , the occurrence of curling was evaluated. .
The results are shown in Table 2. As is clear from Table 2, the laminated water-resistant paper obtained here was curled after LBP printing.

Claims (3)

In laminated water-resistant paper in which layers of one or more thermoplastic resins are laminated on both sides of a paper substrate, the heat shrinkage stress of the resin layer laminated on the printing surface side is more than the heat shrinkage stress of the resin layer laminated on the back surface. Laminated waterproof paper characterized by being small. The laminated water-resistant paper according to claim 1, wherein the resin layer laminated on the printing surface side is thinner than the resin layer laminated on the back surface. The laminated waterproof paper according to claim 2, wherein the resin layer laminated on the printing surface side is thinner than the resin layer laminated on the back surface by 5 μm or more.