JP4277712B2 - Laminated sheet for image recording - Google Patents

Description

  The present invention is a recording medium for forming an image by electrophotography using, for example, a copying machine or a printer, and in particular, forms a clear color image with abundant color tone, excellent color reproducibility, and excellent gloss. The present invention relates to a laminated sheet suitable for image recording.

  Up to now, as a method for forming a good color image by electrophotography, when a color toner image is fixed on a sheet-like material called a transfer body or a recording medium, the color toner image is pressed by a heat roll. Thus, there is known a method of forming a color image with less unevenness on the surface by heating, melting and fixing so as to be embedded in the surface of the transfer body.

  For example, in Patent Document 1, a transparent resin layer having a layer thickness corresponding to the thickness of the color toner image after fixing is present on the surface of the transfer body, and the color toner image is fixed so as to be embedded in the transparent resin layer. In addition, when a color toner is deposited on a resin layer and heated, melted, and fixed to form a color image, the belt-shaped carrier that moves under a member incorporating a heat source is described. By heating, the color toner adhered on the transparent resin layer on the surface of the transfer body is heated and melted in the transparent resin layer, then cooled and fixed, and the transfer body is further separated from the belt-shaped transport body to form a color image. The method of forming is shown.

  Further, as a transfer body corresponding to a method of forming an image by embedding such a toner, for example, in Patent Document 2, at least a toner image transfer surface of a substrate is composed of two layers, an undercoat layer and an overcoat layer. A recording medium having a thermoplastic transparent resin layer and defining the relationship between the softening points of the toner, the undercoat layer and the overcoat layer is shown.

JP-A-5-216322 JP-A-11-231562

  However, the above-mentioned patent document 2 describes that the undercoat layer has flexibility for embedding toner in the thermoplastic resin as the thermoplastic resin provided on the surface of the recording medium. When the transfer body is to be passed through the nip portion between the heat roll and the pressure roll in a shorter time due to a demand for high speed when being melted and fixed in the resin layer, the resin of the color toner image Insufficient embedding in the layer tends to form irregularities on the surface.

  Another problem with a transfer body having a resin layer on the surface is that the thermoplastic resin on the surface is softened by contacting a fixing unit such as a heat roll in the image forming apparatus. When the resin softens, the surface tone of the hot roll, etc. is copied, the surface properties and gloss are deteriorated and the beauty is impaired, and further, the resin layer on the surface is fused to the hot roll and blocking is caused. .

  Accordingly, an object of the present invention is to provide a method in which a resin layer is present on the surface of a substrate and a color toner is fixed on the resin layer to form a color image. An object of the present invention is to provide a laminated sheet for image recording that is high and has excellent transportability.

The above-described problem is a laminated sheet which is an electrophotographic recording medium in which toner is fixed so as to be embedded in a thermoplastic resin layer, and the laminated sheet is formed on at least one surface of a base material with a thermoplastic resin. 2 or more resin layers are provided, the outermost layer of the two or more resin layers is made of polypropylene or polymethylpentene, and at least one resin layer excluding the outermost layer is made of a polyethylene resin having a melting point of 130 ° C. or less. Thus, the polyethylene resin has a melting point lower than that of the outermost resin, and the difference between the melting point and the Vicat softening point is 50 ° C. or less.

  According to the present invention, as a recording medium for forming an image by electrophotography using a copying machine, a printer, or the like, particularly for an apparatus in which toner is embedded in a resin layer provided on a base material to form an image. Even in such a case, there is no blocking due to sticking to a heat fixing portion or the like in the apparatus, and gloss is not impaired before and after image formation. In addition, the embedding property of the toner in the resin layer is good, an image having an excellent surface feeling with no unevenness on the surface can be obtained, and a color image having gloss similar to a silver salt color image can be obtained. .

The laminated sheet of the present invention is produced by providing at least two resin layers made of a thermoplastic resin on at least one side of a substrate. As the substrate, any of an ordinary opaque substrate for color images and a transparent substrate for OHP can be used. As the former opaque base material, wood pulp fiber paper sheet, coated paper, cast paper, processed paper, synthetic paper, plastic sheet, metal sheet and the like are used. As the latter transparent substrate for OHP, for example, a polyester film such as polyethylene terephthalate, a polyether sulfone film, or the like is used. In order to obtain a color image that is rich in reflected light of the color image and is more excellent in gloss, between the opaque base material and the resin layer, for example, CaO, BaO, SrO, ZnO, TiO ₂ , BaSO ₄ A layer containing a white pigment such as a dispersion may be provided. In order to obtain a laminated sheet with higher gloss, it is preferable to use a substrate having higher gloss such as coated paper or cast paper.

  Examples of the thermoplastic resin present in the outermost layer of the laminated sheet of the present invention include polypropylene resin, polyethylene resin, acrylic resin, styrene-acrylic resin, styrene-butadiene resin, polyvinyl alcohol resin, vinyl acetate resin, polyester resin, polyurethane resin. , Epoxy resin, polyvinyl alcohol resin, and the like, but are not limited thereto. Among these, polypropylene is desirable from the viewpoint of workability and adhesion to a resin used for a layer other than the outermost layer. Moreover, these resin can also use 1 type or 2 types or more together.

  In the present invention, the resin that forms the outermost layer has a function of preventing the laminated sheet from sticking to the heat fixing portion or the conveyance body in the image forming apparatus and causing blocking when the color toner is heated, melted, and fixed. Have. Therefore, the melting point of the resin present in the outermost layer may be selected so as not to be softened or melted excessively when the color toner is heated, melted and fixed. If the melting point is too low, blocking tends to occur, the image becomes rough and the glossiness decreases. The melting point required for these outermost resin layers is determined solely by the relationship with the heating temperature set in the image forming apparatus, but is preferably about 130 ° C. or higher. When two or more kinds of resins are used, the mixture may be adjusted to have a desirable melting point. Moreover, there is no restriction | limiting in the upper limit of melting | fusing point of outermost layer resin, as long as a lamination process is possible and the desired effect is not inhibited.

  Next, as a resin forming at least one layer present between the base material and the outermost layer, for example, polypropylene resin, polyethylene resin, acrylic resin, styrene-acrylic resin, styrene-butadiene resin, polyvinyl alcohol resin, vinyl acetate Resins, polyester resins, polyurethane resins, epoxy resins, polyvinyl alcohol resins, and the like can be mentioned, but are not limited thereto.

  In the present invention, the resin forming at least one layer excluding the outermost layer has a function of imparting flexibility for embedding the toner when the color toner is heated, melted, and fixed. Therefore, the melting point of such a resin should be selected so as to be lower than that of the outermost resin and to sufficiently embed the color toner. Similarly to the outermost layer resin, this may be adjusted as appropriate according to the temperature setting of the image forming apparatus, but it is preferable that the temperature is lower than 130 ° C., more preferably 125 ° C. or lower.

  However, the present invention further finds that the difference between the melting point and the Vicat softening point is important for the resin forming at least one layer excluding the outermost layer. When focusing only on the melting point or softening point of the resin, the color toner can be sufficiently embedded while the transfer body passes through the nip portion between the heat roll and the pressure roll in a short time even if each is low. It is not always so soft, and as a result, a color image having unevenness on the surface is likely to be formed.

  The Vicat softening point, as shown in JIS K7206, depends on the temperature when a certain load of weight is placed on a resin piece, the resin piece is heated, and the resin softens and the weight sinks to a certain depth. It is determined. That is, the Vicat softening point represents the temperature at which the resin becomes a certain softness, and the difference between the melting point and the Vicat softening point means the degree of variation in the resin molecular weight. The polymer compound constituting the resin is formed by connecting unit compounds (monomers), and the molecular weight of the polymer compound is determined by the number of monomers. The softening temperature varies depending on the molecular weight. Therefore, the higher the resin composed of a polymer compound in which the same number of monomers are connected, the more the softening points are aligned and the smaller the difference from the melting point. On the other hand, if the molecular weight varies, it can be said that the difference between the melting point and the melting point is large because the temperatures at which softening begins are different. Therefore, it is considered that the greater the difference between the softening point and the melting point, the longer it takes for the toner to be sufficiently softened after the resin layer starts to soften, and the toner embedding in a short time becomes insufficient. .

  In the present invention, the difference between the melting point and the Vicat softening point is preferably as small as possible, and is 50 ° C. or lower, more preferably 30 ° C. or lower. An excellent color image can be formed. Two or more kinds of resins may be mixed and adjusted to have such a difference between the melting point and the Vicat softening point.

  The outermost layer or the other thermoplastic resin layer can be usually formed by extrusion-laminating or co-extrusion-laminating a thermoplastic resin on a substrate. Moreover, as long as desired performance can be ensured, the resin layer may be formed using any known coating method.

  The thickness of the outermost layer of the resin layer is not particularly limited as long as a desired function can be exhibited, but is 1 to 15 μm, preferably about 3 to 12 μm. If the thickness of the outer layer of the resin layer is excessive, when the color toner image is heated, melted and fixed, it becomes difficult to be sufficiently embedded in the resin layer, and a color image with many irregularities is formed. On the other hand, if the layer thickness of the outermost layer is too small, the resin layer between the substrate and the outermost layer is not sufficiently coated, and when the color toner is heated, melted, and fixed, the softened resin other than the outermost layer is directly fixed. There is a possibility that the image is rough and glossiness is lowered due to contact with the portion.

  Further, the layer thickness of the resin layer in which the difference between the melting point and the Vicat softening point laminated to at least one layer excluding the outermost layer is 50 ° C. or less is not particularly limited as long as it can exhibit a desired function, but is 20 μm or more, 200 μm or less, Preferably they are 25 micrometers or more and 180 micrometers or less. If the thickness is too small, when the color toner image is heated, melted and fixed, it is not sufficiently embedded in the resin layer, and a color image with many irregularities is formed. Even if it is excessively large, the effect of embedding the color toner reaches its peak, which is disadvantageous in terms of cost.

  The thermoplastic resin layer may be provided on one side or both sides of the substrate, but the layer made of a resin having a melting point lower than that of the outermost layer resin and having a difference between the melting point and the Vicat softening point of 50 ° C. or less is an image. In the forming apparatus, it is essential to be present on the side that is in contact with the heat roll or the like and becomes the toner fixing surface. In terms of cost, the structure in which the base material, the resin layer having a lower melting point than the resin of the outermost layer and the difference between the melting point and the Vicat softening point is 50 ° C. or less, and the outermost layer are sequentially laminated is the most economical. Yes, a sufficient effect can be obtained with a simple structure, but between the base material and a layer made of a resin having a lower melting point than the resin of the outermost layer and a difference between the melting point and the Vicat softening point of 50 ° C. or less, Alternatively, one or more layers made of the above-described types of thermoplastic resins or the like can be appropriately provided between this layer and the outermost layer. Similarly, when the thermoplastic resin layer is provided on the opposite surface, there is no particular limitation, and the above-described resin or other resin is used, and the thickness or the manufacturing method is appropriately adjusted according to the quality performance required for one or more layers. What is necessary is just to laminate. Of course, both sides may have the same laminated structure.

In addition, a layer for the purpose of improving the adhesion to the color toner or imparting electrical characteristics of the surface to the surface of the outermost layer may be applied to the surface of the outermost layer without affecting the desired effect. You may provide by an engineering process. Specifically, for example, an antistatic agent containing a known acrylic resin as a main component may be added to obtain electrical characteristics.
In addition, a new layer is added to the layers other than the outermost layer of the resin layer for the purpose of improving the adhesion between the resin layers or between the base material and the resin layer, as long as the desired effect is not affected. It may be provided.

  Hereinafter, the present invention will be described based on examples, but the present invention is not limited thereto. In the obtained Examples and Comparative Examples, the glossiness, toner embedding property, and sticking property with the fixing unit of the apparatus were evaluated as follows, and the results are shown in Table 2. The melting point was measured according to JIS K7121, and the Vicat softening point was measured according to JIS K7206.

<Glossiness>
The 75 ° glossiness of the white paper portion was measured according to JIS P-8142.
<Toner embedding>
The side of the laminated sheet on which the resin is present is used as a toner fixing surface. After the toner is attached with a Canon iRC3200, a PET film having a thickness of 75 μm with good releasability from the toner is superimposed on the toner fixing surface, and the temperature is 140 After passing through a heat roll at 0 ° C. at a speed of 6 mm / sec, the degree of toner embedding in the obtained image was visually evaluated.
A: The toner is sufficiently embedded, and there are no irregularities in the image area and the non-image area. O: The toner is embedded, and there are almost no irregularities in the image area and the non-image area. It is not embedded in the image, and there are irregularities in the image area and non-image area.
The side of the laminated sheet on which the resin is present is used as a toner fixing surface. After the toner is adhered by Canon iRC3200, a PET film having a thickness of 75 μm with good releasability from the toner is superimposed on the toner fixing surface, and 150 ° C. The change in the degree of crushing of images (characters) when subjected to heat and pressure treatment at 3 kg / cm ² was visually evaluated.
○: The characters are not crushed and the image quality is good.
X: The character is crushed and the image quality is deteriorated.
<Adhesiveness>
The surface of the blank sheet laminated resin is superimposed on the glossy surface of the 10 μm thick aluminum film, and further the 75 μm thick PET film is superimposed on the non-glossy surface of the aluminum film at a temperature of 140 ° C. After passing through the heat roll at a speed of 6 mm / sec, it was allowed to stand until it reached room temperature, and the sticking property when the resin-exposed surface of the laminated sheet and the glossy surface of the aluminum film were peeled was evaluated.
○: Adhesion is not observed △: Adhering slightly, but the sheet surface is not destroyed ×: Adhesion is observed and cannot be removed, or the sheet is destroyed when it is removed

[Example 1]
A low density polyethylene (hereinafter referred to as LDPE: melting point 55 ° C., Vicat softening point 52 ° C.) melt as an inner layer and a polypropylene (hereinafter referred to as PP: melting point 160 ° C.) melt as an outer layer have a basis weight of 155 g / m ² . A laminated sheet was produced by coextrusion lamination at an extrusion temperature of 300 ° C. using a T-die so that the LDPE melt was laminated on one side of the high-quality paper.
That is, this laminated sheet has a laminated structure of PP layer / LDPE layer / cast paper. At this time, the thicknesses of the PP layer and the LDPE layer were 5 μm and 25 μm, respectively.

[Examples 2 to 6 , Comparative Examples 1 to 3 ]
A laminated sheet was produced in the same manner as in Example 1, except that the type, melting point, softening point, and layer thickness of the resin in Example 1 were as shown in Table 1. In the table, the outer layer resin of Example 5 is polymethylpentene (TPX). The “difference” of the inner layer indicates “melting point−softening point”.

Claims (1)

A laminated sheet, which is an electrophotographic recording medium in which toner is fixed so as to be embedded in a thermoplastic resin layer and forms an image, wherein the laminated sheet comprises two or more thermoplastic resins formed on at least one surface of a substrate. The outermost layer of the two or more resin layers is made of polypropylene or polymethylpentene, and at least one resin layer excluding the outermost layer is made of a polyethylene resin having a melting point of 130 ° C. or less, and the polyethylene A laminated sheet characterized in that the resin has a lower melting point than the resin of the outermost layer, and the difference between the melting point and the Vicat softening point is 50 ° C. or less.