JP2019188663A - Sheet - Google Patents

Abstract

To provide a sheet which enables clear printing even at the time of high-speed printing by an off-set method.SOLUTION: A sheet has a layer containing a pigment and a binder as main components on at least one surface on a support, in which the support contains an inorganic filler and a thermoplastic resin in a mass ratio of 40:60 to 85:15. In the sheet, water absorbency by JISP8140 cup method of a surface having a layer containing a pigment and a binder as main components is 0.1 to 20 g/m2 minutes, a surface having the layer containing the pigment and the binder as the main components has a hole 1 having an average diameter of 0.1-3.0 μm, and the total sum of the area of the hole 1 is 1.0-10.0% of the surface.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sheet and particularly relates to a sheet excellent in printability and water resistance.

  The printing used in the world is overwhelmingly offset printing. In offset printing, a PS plate in which an oleophilic photosensitive agent is applied to a hydrophilic aluminum support is used in the plate making process, and the non-image area oleophilic portion having no pattern is removed by exposure. When the plate made in this way is applied to the plate cylinder in the printing process and printed, an aqueous solution called dampening water is placed on the part from which oleophilicity has been removed, followed by oleophilic ink. Ink is applied only to the pattern.

  The ink transferred to the plate cylinder is once transferred to a rubber cylinder called a blanket and then transferred to the paper of the printing medium. In offset printing, a dampening solution can be used to perform very clear printing, and because the wear of the plate cylinder is small, large-scale printing is possible.

  In general, paper made from wood pulp has some degree of suitability for offset printing, but is inferior in water resistance. Therefore, a printing sheet based on a plastic film or a thermoplastic resin sheet has been proposed. In this case, the resin molded body sheet is microporous with good air permeability when dried by a cast method. Is selected (Patent Document 1). Accordingly, in this case as well, water absorption is inevitable because the substrate is microporous.

  On the other hand, as a method for imparting printability to a resin molded sheet, a method of providing a coating layer corresponding to UV or radiation on the surface of the sheet has been proposed in order to improve the adhesion with ink (Patent Document 2). The coating layer is a resin layer containing 70% by mass or more of a synthetic polymer such as urethane or acrylic.

  Since the resin molded body sheet as described above cannot absorb dampening water inside like paper, the dampening water remains on the surface when these sheets are printed at high speed by the offset method. There was a problem that emulsification occurred when mixed with the supplied ink, and clear printing was not achieved.

Japanese Patent Laid-Open No. 2-253881 Japanese Patent Laid-Open No. 2006-166865 Patent No. 6095694 JP 2009-138317 A

As a resin molded body sheet, a sheet having a Cobb method water absorption of 20 g / m ² · 2 minutes, preferably 11 g / m ² · 2 minutes has been proposed (Patent Document 3). This sheet is known to have good water resistance.
However, unlike the microporous resin molded body, in the case of the resin molded sheet having good water resistance as described above, a product that can sufficiently cope with offset printing using dampening water has not been obtained.

  An object of the present invention is to provide a sheet that enables clear printing even during high-speed printing by an offset method and has excellent water resistance.

The inventors achieved the object of the present invention by the following.
1. A sheet having a layer mainly composed of a pigment and a binder on at least one surface of a support, the support containing an inorganic filler and a thermoplastic resin in a mass ratio of 40:60 to 85:15 The water absorption by the JISP 8140 cup method on the surface having the layer mainly composed of the pigment and binder is 0.1 to 20 g / m ² · 2 minutes,
The sheet | seat in which this binder contains 20-60 mass parts aqueous dispersion resin with respect to 100 mass parts of pigments.
2. The surface having the layer mainly composed of the pigment and the binder has pores having an average diameter of 0.05 to 3.0 μm, and the total area per unit area of the pores is 1.0 to 10.0 of the unit area. The sheet according to 1 above, which is%.
3. 3. The sheet according to 1 or 2, wherein the thermoplastic resin is mainly composed of at least one selected from polyethylene resin and polypropylene resin.

  According to the present invention, it is possible to provide a printing sheet that enables clear printing even during high-speed printing by the offset method and has excellent water resistance.

It is a figure which shows the hole which exists in the coating layer surface of the support body 1 of this invention. It is a figure which shows the hole which exists in the coating layer surface of the support body 2 of this invention. It is a figure which shows the hole which exists in the coating layer surface of the support body 3 of this invention. It is a figure which shows the hole which exists in the coating layer surface of the support body 4 of this invention. It is a figure which shows the coating layer surface of the support body X of a comparison.

Hereinafter, embodiments of the present invention will be described in detail.
The sheet of the present invention is a sheet having a layer mainly composed of a pigment and a binder (hereinafter sometimes abbreviated as a coating layer) on at least one surface of the support, and the support is filled with an inorganic material. The material and the thermoplastic resin are contained in a mass ratio of 40:60 to 85:15, and the water absorption by the JISP8140 cup method on the surface having the coating layer is 0.1 to 20 g / m ² · 2 minutes. It is characterized by.

The water absorption of the sheet of the present invention is much less than that of the sheet used for general offset printing, which is 50-60 g / m ^{2 ·} 30 seconds or more (Patent Document 4). It is.
In order to obtain good offset printing characteristics that do not cause an emulsification phenomenon while obtaining the above results, the present inventors have the presence of ultrafine pores that cause capillary action on the sheet surface rather than water absorption. Found that is necessary.

  That is, the inventors used a support containing an inorganic filler and a thermoplastic resin in a mass ratio of 40:60 to 85:15, and the pigment and binder as the main components on the support. It was found that a sheet excellent in offset printability and water resistance can be obtained by providing a coating layer having the fine pores.

<Support>
The support of the present invention contains an inorganic filler and a thermoplastic resin in a mass ratio of 40:60 to 85:15. The total amount of the inorganic filler and the thermoplastic resin is 80 to 100% by mass of the support.
The support of the present invention is required to have whiteness and opacity for suitability as a printing sheet. The whiteness is 78 to 95% (measured according to JIS P8148), and the opacity is 80 to 95% (measured according to JIS P8149). Preferably, the whiteness is 80 to 95% and the opacity is 85 to 95%.
The film thickness of the support of the present invention is 25 to 300 μm, and is appropriately selected depending on the purpose of printing.

≪Inorganic filler≫
Examples of the inorganic filler contained in the support of the present invention include calcium carbonate, titanium oxide, silica, kaolinite (generally called kaolin clay), talc, aluminum hydroxide and the like, and calcium carbonate is particularly preferable. These may be used alone or in combination of two or more. In order to improve the dispersibility or reactivity of the inorganic filler, the surface of the inorganic filler may be modified in advance according to a conventional method.

  The inorganic filler is preferably particles, and the average particle size is preferably from 0.1 μm to 50 μm, and more preferably from 1.0 μm to 15 μm. The average particle diameter of the inorganic filler in the present invention is a 50% particle diameter (d50) obtained from an integrated% distribution curve measured with a laser diffraction particle size distribution analyzer.

≪Thermoplastic resin≫
Although it does not specifically limit as a thermoplastic resin of this invention, For example, polyolefin resin (polypropylene resin, polyethylene resin, etc.), biodegradable resin, polyamide resin, polybutylene terephthalate (PBT), polyethylene terephthalate (PET) etc. are mentioned. It is done. Of these, polyolefin resins and biodegradable resins are preferable, and at least one selected from polyethylene resins and polypropylene resins is particularly preferable. A main component means the quantity exceeding 50 mass% of the whole thermoplastic resin.

  In addition, polyolefin resin and polyamide resin refer to resin which has polyolefin and polyamide as a principal chain. More specifically, for example, a polypropylene resin refers to a resin having polypropylene as a main chain, and these resins preferably have crystallinity and may be copolymers with other resins. For example, a propylene-ethylene copolymer may be used.

  The biodegradable resin is a resin that is completely consumed by microorganisms in the natural world and is finally decomposed into water and carbon dioxide.

  Specific examples include polylactic acid, polycaprolactone, polybutylene succinate, polybutylene adipate, polyethylene succinate, and cellulose ester. The crystalline polymer may be used alone or in combination of two or more. For example, a mixture of a polypropylene resin and a polyethylene resin may be used. Of these, it is particularly preferable to use polypropylene resin or polyethylene resin.

  The support of the present invention contains an inorganic filler and a thermoplastic resin in a mass ratio of 40:60 to 85:15, preferably 55:45 to 80:20.

≪Other ingredients≫
In the support of the present invention, in addition, one or more auxiliary agents selected from among lubricants, antioxidants, ultraviolet absorbers, coloring pigments, dispersants, compatibilizers, antistatic agents, flame retardants, etc. Can be added within a range not detrimental to the purpose. Preferably, it is 0.1-20 mass% of a support body.

≪Support manufacturing method≫
The support of the present invention can be produced by a known method. For example, Japanese Patent No. 5461614 can be referred to.

<Layer mainly composed of pigment and binder>
The layer mainly composed of the pigment and binder of the present invention (hereinafter also referred to as a coating layer) is composed of the pigment and the binder.

≪Pigment≫
As the pigment of the present invention, both organic pigments and inorganic pigments can be used, and they can be used in combination. The average particle size is preferably 0.01 to 5 μm, and specifically, kaolinite (generally called kaolin clay), aluminum hydroxide, calcium carbonate, titanium dioxide, barium sulfate, zinc oxide, silica , Polystyrene particles, polymethyl methacrylate particles and the like.
The pigment of the present invention is preferably used by mixing pigment 1 having an average particle diameter of 1 to 7 μm and pigment 2 having an average particle diameter of 0.02 μm or more and less than 1 μm. The mixing mass ratio is preferably Pigment 1: Pigment 2 = 50: 50 to 85:15.

≪Binder≫
The binder of the present invention is preferably an aqueous binder that can be applied aqueous. As aqueous binder, aqueous dispersion resin such as styrene / butadiene latex, acrylic latex such as copolymer of acrylic acid ester and methacrylic acid ester, casein, starch, polymelacrylic acid and its salt, polyvinyl alcohol, carboxymethyl cellulose, etc. Any water-soluble adhesive can be used or used in combination.

  The inventors have further shown that the amount of the binder of the aqueous dispersion resin is particularly important, and the content of the aqueous dispersion resin such as styrene-butadiene latex is preferably 20 parts by mass or more, preferably 100 parts by mass of the pigment. When it is 25 parts by mass or more, more preferably 30 parts by mass or more, the adhesion between the coating layer and the support becomes strong, the printing strength of the present invention is increased, and it becomes easy to adjust the water absorption to a preferable range, It has been found that the water resistance is greatly improved.

  Generally, when the content of the aqueous dispersion resin exceeds 20 parts by mass with respect to 100 parts by mass of the pigment, migration occurs when the applied coating liquid is dried, a resin film is formed on the sheet surface, and the printability is increased. In the support of the present invention, the occurrence of migration is suppressed.

≪Method for producing coating layer≫
The coating layer of this invention can provide the coating liquid on a support body using a normal coating coater and a drying apparatus after preparing the coating liquid containing a pigment and a binder. In addition to the pigment and binder of the present invention, additives such as pigment dispersants, viscosity modifiers, antifoaming agents and the like that are usually used in coating solutions can be appropriately used for the coating solution.

The concentration of the coating liquid is generally 20 to 75% by mass as a solid content, and can be appropriately adjusted and selected depending on the desired thickness, viscosity, coater type, and the like of the coating layer. This coating layer has a coating amount after drying of 0.5 to 30 g / m ² , preferably 1 to 20 g / m ² , and a coating film thickness after drying of 1 to 20 μm.
Before forming the coating layer of the present invention, it is preferable to perform a treatment such as corona discharge on the support, or an undercoat layer of an aqueous binder such as a 0.1 to 0.5 μm latex may be provided. .

<Properties of coating layer>
The surface having the coating layer of the present invention, the water absorbency by cup method JISP8140 is 0.1~20g ^{/ m 2/2} minutes. The water absorption is such that the surface having the coating layer has pores having an average diameter of 0.1 to 3.0 μm, and the total area per unit area of the pores is 1.0 to 10.0% of the unit area. Is achieved.

In the measurement of the hole size of the present invention, a technique for measuring the size of a submicron-sized hole by concomitant with gold vapor deposition at the time of observation with a scanning electron microscope is devised, and the sum of the average diameter and the area of the hole Asked. As an electron microscope, Keyence ultra-deep multi-angle microscope DVHX-5000 and its associated image processing software were used.
The total diameter and area of the pores can be adjusted mainly by the type and amount of pigment used in the coating layer (Example 2), as well as by the drying conditions and the resin type of the support. Can do.

  FIG. 1 shows an SEM electron microscope image of the surface having the coating layer. The black part is the hole part. This hole is considered to have a capillary structure that extends in the thickness direction of the coating layer and absorbs dampening water during printing.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples.
(Example 1)
<Production of support>
The surface-treated average particle diameter (D50) is 5.8 μm calcium carbonate powder, high-density polyethylene resin (MFR 0.3 g / 10 min), polypropylene resin (MFR 0.5 g / 10 min) is 60:20:20. Raw materials obtained by adding additives such as lubricants and antistatic agents to the main components contained in a mass ratio are extruded by a direct method using a co-rotating twin screw extruder (screw diameter 100 mm and kneading temperature 210 ° C.). Then, it was made into a resin body sheet, and the sheet was stretched 1.5 times by roll stretching to obtain a support body 2 of the present invention, and a support body 1 in which the resin composition and the stretching ratio were changed as shown in Table 1. 3 and 4 were produced in the same manner.

  Table 1 shows physical property values of the supports 1 to 4. PP stands for polypropylene resin, and PE stands for polyethylene resin.

<Preparation of coating layer>
≪Preparation of coating liquid≫
As inorganic materials, 70 parts by weight of kaolin clay (97% of particle size less than 2 μm) and 30 parts by weight of light calcium carbonate (particle size of 0.05 to 0.1 μm) are used, and a dispersant (sodium polyacrylate aqueous solution, solid content) A uniform slurry of inorganic material was prepared by adding kaolin clay and light calcium carbonate in this order to water in which 1 part by mass of 43%, molecular weight MW = 6000) was previously dissolved.

Furthermore, as an aqueous binder, styrene-butadiene latex (solid content 48% by mass, Tg = −12 ° C., average particle size 170 nm) and dextrin (DE 10) are each 34% by mass in solid content with respect to the inorganic material. It was used at a ratio of mass%, and was sequentially added to the slurry of the inorganic material and stirred with a mixer to prepare a uniform coating solution 1. The solid content concentration of the coating liquid 1 was 50.5% by mass, and the viscosity measured by a B-type viscometer was 170 mPa · s at 60 rpm and 25 ° C.
Coating liquids 2 and 3 were also prepared with kaolin clay and light calcium carbonate in parts by mass ratios of 75:25 and 65:35, respectively.

≪Preparation of coating layer≫
While applying corona discharge on the supports 1 to 4, the prepared coating liquid was applied with a micro gravure (MG) type coating machine (coating width max 1520 mm), the MG roll was driven by an AC servo motor, and the MG rotation speed Was applied so as to have a dry film thickness of 10 g / m ² under the condition of max 900 rpm, and dried at a drying temperature of 90 to 130 ° C. and a wind speed of about 10 m / second in a drying furnace having a total length of 17 m, and a coating layer was provided on both sides. Sheets 1 to 4 were produced.

For comparison, a comparative sample X was prepared in the same manner as described above except that the solid content ratio of the styrene / butadiene latex was 20 mass% with respect to the inorganic material among the preparation conditions of the coating liquid.
As shown in FIGS. 1 to 4, it is observed that holes having an average diameter of 0.05 to 3.0 μm are scattered (in addition to the circle in FIG. 1, one memory is 1 μm). ). On the other hand, as shown in FIG. 5, in the comparative sample X, no scattered holes having an average diameter of 0.05 to 3.0 μm are observed (one memory is 2 μm). All scales are 5000 times.

[Measurement method of water absorption]
According to JISP8140 cup method.
[Measurement method of average diameter and area of holes]
Holes, using a super-depth multi-angle microscope VHX5000 manufactured by Keyence Corporation, in combination with gold deposition was observed, the number of field 3350Myuemu ² per hole, the total area of the holes was determined by software attached, from that value The average diameter of one hole was calculated.
[water resistant]
Each sheet was immersed in water at 25 ° C., and the state after standing for 3 days was visually observed.
○: No peeling occurred.
×: Peeling occurs

<Printability test>
A printing test (using a test plate) with the following actual machine was performed.
・ Printer: RYOBI 920 OFFSET PRESS UV (LED)) 4 colors uv
・ Printing speed: 9,000rpm
-Ink for printing: General ink for UV-Number of printed sheets: 500 sheets of each of the four types of sheets described in the examples were printed.
In the test, a practical visual sensory evaluation was performed. Details of the evaluation are shown in Table 4. In addition, the surface strength and printability of the sheet were evaluated according to the following.

[Measurement of surface strength]
Immediately after printing and 24 hours later, the surface strength was determined by the presence or absence of peeling with a cellophane tape. Immediately after printing, after 24 hours, no peeling, ◎, after 24 hours, no peeling, ○, immediately after printing, after 24 hours, peeling, of which there is a possibility of improvement by changing printing ink △, and the thing which has no possibility of improvement was made into x.

[Evaluation of printability]
Observe the printed surface with the naked eye, determine the print unevenness, print density, smoothness of the printed surface, etc., and refer to the print density on the solid surface as ◎. And the evaluation in the meantime is indicated as ◯ and △.

(Example 2)
It shows that the average diameter and the total area of the holes can be adjusted by applying the coating liquids 2 and 3 to the support 2 and preparing a sheet having a coating layer. The results are shown in Table 5.

  1 hole

Claims (3)

A sheet having a layer mainly composed of a pigment and a binder on at least one surface of a support, the support containing an inorganic filler and a thermoplastic resin in a mass ratio of 40:60 to 85:15 The water absorption by the JISP 8140 cup method on the surface having the layer mainly composed of the pigment and binder is 0.1 to 20 g / m ² · 2 minutes,
The sheet | seat in which this binder contains 20-60 mass parts aqueous dispersion resin with respect to 100 mass parts of pigments.   The surface having the layer mainly composed of the pigment and the binder has pores having an average diameter of 0.05 to 3.0 μm, and the total area per unit area of the pores is 1.0 to 10.0 of the unit area. The sheet according to claim 1, which is%.   The sheet according to claim 1 or 2, wherein the thermoplastic resin contains at least one selected from a polyethylene resin and a polypropylene resin as a main component.