JP2008221599A - Water-resistant laminate sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-resistant laminate sheet having superior ink-drying properties and superior tight adhesiveness to the substrate and enabling printing with an ink for general coated paper sheets. <P>SOLUTION: The water-resistant laminate sheet has a coating layer on a laminate sheet having a thermoplastic resin layer. The laminate sheet having a thermoplastic resin layer has at least one thermoplastic resin layer on one or both sides of a sheet-formed substrate, and the outermost layer of the thermoplastic resin layers is made of a thermoplastic resin comprising at least one selected from (A) low-density polyethylenes of a density of 0.85-0.29 g/cm<SP>3</SP>and a melt flow rate, MFR by JIS K6922-2, of 3-20 g/min and (B) polyethylene and polypropylene type resins, ethylene-acrylate copolymer resins and styrene-butadiene copolymer resins, with a content of resins (A) of ≥50 wt.%. The coating layer is formed on at least one surface of the thermoplastic resin layer of the laminate sheet and based on an inorganic pigment and a binder, and the inorganic pigment contains colloidal silica with primary particles being spherical and in a ratio of the particle size of secondary particles to that of primary particles of 1.5-3.0 or needle-like colloidal alumina. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a water-resistant laminated sheet obtained by laminating a thermoplastic resin layer on a substrate, and particularly to a laminated sheet suitable for offset printing.

Currently, as a laminated sheet having water resistance, a composite paper type laminated sheet (Patent Document 1) obtained by laminating a thermoplastic resin containing an inorganic filler on a paper substrate or the like, and an inorganic filler or foam on a thermoplastic resin. Synthetic paper type products that are kneaded and stretched are known, and are used in various fields that require water resistance, such as posters, labels, delivery slips, and packaging of frozen and refrigerated foods. A composite paper type laminated sheet is usually produced by an extrusion lamination method, a coextrusion lamination method, a dry lamination method, or the like. That is, a thermoplastic resin melted from a T-die film forming machine is extruded onto the surface of a substrate fed from a winding roll, or two or more kinds of thermoplastic resins are coextruded, and immediately between a cooling roll and a nip roll. The base material and this (these) thermoplastic resin layer are pressed and pressure-bonded and laminated, or a thermoplastic resin film formed on the base material is bonded by an adhesive or the like. However, these laminated sheets are hardly soaked with ink on the surface as they are. Therefore, when this is used for various types of printing such as offset printing, the printed ink stays on the sheet surface and dries as it is. Therefore, when the printed sheet is rubbed, the dried ink peels off from the sheet surface. Or the surface of the sheet is crushed and the printed surface is soiled.
One method for preventing such trouble is to form an ink layer more firmly on the sheet surface. For example, a commercially available ink for synthetic paper uses a solvent mainly composed of vegetable oil containing many unsaturated bonds, and solidifies the ink by oxidative polymerization, thereby strengthening the ink layer on the sheet surface. This synthetic paper-dedicated ink can be used not only for synthetic paper but also for composite paper. By using this ink, it is possible to obtain an excellent printing surface that does not disappear or become dirty due to friction. On the other hand, this ink takes a very long time to be completely solidified, and it is necessary to take a long waiting time until it is sent to the next process after printing. If this time is insufficient, when the printed sheets are stacked and stored, there is a problem (backing) that the ink on the sheet surface is transferred to the back surface of the sheet stacked thereon. In addition, since such an ink is solidified by reacting with oxygen in the air, solidification starts during printing, the viscosity of the printing ink increases, and the stable operation of the printing press may be hindered.

Therefore, as another method for improving the printability of the laminated sheet, it is conceivable that a coating layer containing an inorganic pigment or the like is provided on the surface of the sheet as an ink receiving layer, and an ink receiving layer for absorbing ink is provided on the coating layer. . If it is this method, the ink for offset printing etc. conventionally used widely for general coated paper can also be used. However, in order to sufficiently absorb the printed ink in such a coating layer and prevent it from staying on the surface of the coating layer, it usually contains a lot of inorganic pigments such as titanium oxide, calcium carbonate, clay, talc and silica. Although it is necessary to provide a coating layer, both composite paper and synthetic paper are provided on the surface of the thermoplastic resin, so they are easily detached from the surface of the thermoplastic resin and have their own surface strength. Also become weaker. In applications where gloss is required, blending of pigments such as inorganic pigments such as titanium oxide, calcium carbonate, clay, talc and silica leads to a decrease in gloss and is not preferred. On the other hand, in the coating layer containing a large amount of binder as in the water-resistant sheet of Patent Document 2, detachment from the surface of the thermoplastic resin, surface strength and glossiness of the coating layer are improved, but the printed ink Is not necessarily sufficient, and is inferior in blocking resistance. For this reason, it is difficult to say that the water resistant sheet thus obtained is excellent in offset printability as a whole.
Patent Document 3 describes an offset printing film in which an ink fixing layer mainly composed of modified polyvinyl alcohol and colloidal silica is provided on a thermoplastic film. Patent Document 4 describes a resin coating film capable of offset printing containing a silica pigment containing colloidal silica with respect to a specific polyvinyl alcohol on a polyolefin film. Patent Document 5 discloses that the outermost layer is at least one selected from petroleum resins, ethylene / α-olefin copolymer resins, α-olefin copolymer resins, high-pressure low-density polyethylene resins, and polystyrene resins. They describe a laminated waterproof sheet comprising a non-charged ionomer resin, low density polyethylene as the outermost layer of the thermoplastic resin (LDPE: MFR11g / 10min, density 0.916 g / cm ^3, a melt tension 1.3 g) 70 weight % Containing examples are described. Patent Document 6 describes an example in which 80% by weight of low density polyethylene (LDPE: MFR 11 g / 10 min, density 0.916 g / cm ³ ) is contained as the outermost thermoplastic resin.

Japanese Patent No. 2763011 JP 2004-223882 A JP 2001-239741 A JP 2000-71596 A JP-A-7-68713 JP 7-47642 A

  Among the uses for which laminated sheets are used, beauty is the most important factor for outdoor posters for elections and commercial use. However, since the paper used as the base material of the laminated sheet is generally composed of intricately intertwined plant fibers and the like, there are innumerable minute irregularities on the surface, and the paper is not flat and thin on the paper base material. The molten resin extruded into a film shape is laminated following the unevenness of the paper, and minute depressions are scattered on the surface of the laminated sheet. When offset printing or the like is performed, there is a problem in that the ink is not transferred to the dent and so-called white spots occur, and the beauty of the finished printed matter is impaired. In addition, in the laminated sheet, it is necessary to have high substrate adhesion so that delamination does not occur between the substrate and the thermoplastic resin layer, but the adhesion between the substrate and the thermoplastic resin layer is compatible. It tends to decrease when a plurality of bad resins are mixed and used, and this also causes the appearance to be damaged. Moreover, when providing the coating layer containing an inorganic pigment etc., there exists a problem that it is difficult to make the sheet | seat surface high gloss. Therefore, if the surface has a low gloss, relatively good ink drying can be imparted, but there is a limit to imparting ink drying properties while maintaining high gloss. Moreover, even if it is a low gloss thing, a higher degree of ink drying may be required. The low-density polyethylene used in Patent Documents 1 and 2 is a relatively soft resin and has good adhesion to the substrate, but it cannot be said that the ink drying property is sufficient. Furthermore, lithographic offset printing is a method in which normal printing is printed directly from the plate surface onto the paper surface, whereas the ink image is once transferred from the plate surface to the rubber blanket surface and then printed onto a substrate such as paper. Yes, fountain solution is used to prevent ink from adhering to the non-image area of the plate surface, but water-resistant sheets made of thermoplastic resin on the surface absorb moisture compared to plain paper such as fine paper and coated paper. Due to the small capacity, if the amount of dampening water increases, dampening water may remain on the paper surface, resulting in poor ink transfer, or the dampening water may be mixed and emulsified on the printing press, resulting in dampening water. The printing workability is inferior, for example, because it is necessary to set a smaller value than usual (the adjustment range is narrow).

  Based on such problems, the present invention has excellent adhesion to the base material, good aesthetics, and excellent ink drying properties by imparting high ink absorption to the thermoplastic resin layer itself. An object of the present invention is to provide a water-resistant laminated sheet that can be printed using a printing ink.

  As a result of intensive studies, the present inventors have determined that the outermost thermoplastic resin layer of the laminated sheet contains low-density polyethylene and a specific other resin, and is further specified on the surface of such composite paper or synthetic paper. The present invention was completed by finding that the above-mentioned problems can be solved by providing a coating layer containing as a main component an inorganic pigment. The main configuration of the present invention is as follows.

(1) In a water-resistant laminated sheet in which a coating layer is formed on a laminated sheet having a thermoplastic resin layer,
A laminated sheet having a thermoplastic resin layer is a laminated sheet in which one or more thermoplastic resin layers are laminated on one or both surfaces of a sheet-like substrate, and the outermost layer of the thermoplastic resin layer is the following resin. (A) and a thermoplastic resin obtained by mixing at least one selected from the group (B), and contains 50% by weight or more of the thermoplastic resin of the following resin (A),
The coating layer is a coating layer mainly composed of an inorganic pigment and a binder on at least one surface of the thermoplastic resin layer of the laminated sheet, and the primary particles are spherical and the primary particles as the inorganic pigment. A water-resistant laminated sheet comprising colloidal silica having a ratio of secondary particle diameter to diameter of 1.5 to 3.0 or acicular colloidal alumina.
(A) Low density polyethylene having a density of 0.85 to 0.92 g / cm ³ and a melt flow rate (MFR (JIS K6922-2)) of 3 to 20 g / 10 min. (B) Polyethylene resin, polypropylene resin, ethylene The water-resistant laminated sheet according to (1), comprising 50 to 90% by weight of a thermoplastic resin of acrylate copolymer resin, styrene-butadiene copolymer resin (2) resin (A).
(3) The thermoplastic resin (B) is linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene (PP), ethylene / methyl acrylate copolymer (EMA), ethylene / ethyl acrylate copolymer. The water-resistant laminated sheet according to (1) or (2), which is either a product (EEA) or a styrene-butadiene copolymer (SBR).
(4) The water-resistant laminated sheet according to any one of (1) to (3), wherein the binder of the coating layer is at least one selected from a styrene, butadiene, (meth) acrylic acid polymer or copolymer. .

The present invention has the following effects in particular.
(1) The present invention using peanut-shaped colloidal silica containing 50% by weight or more of low-density polyethylene as the resin A provided by the present invention and further forming secondary particles as an inorganic pigment to be blended in the coating layer The water-resistant laminated sheet exhibits quality that satisfies both substrate adhesion and ink drying properties, and even when a large amount of dampening water is used, ink transfer is suppressed, resulting in water resistance with a better balance of quality. It is what you play.
(2) In the outermost thermoplastic resin layer, by mixing low-density polyethylene as a main component and a specific other resin, the balance between substrate adhesion and ink drying is excellent.
(3) Because it has excellent ink drying and blocking resistance during printing, it does not take a long time to dry the ink, and the process after printing can be advanced promptly without causing problems such as lining. The printer can be operated stably.
(4) It is excellent in glossiness and enables a print finish excellent in beauty.
(5) The behavior with respect to the fountain solution during offset printing is stable, and the printing workability is improved.

  In the present invention, the laminated sheet provided with the coating layer may be any sheet as long as it has a thermoplastic resin layer as one or both outermost layers of the sheet. That is, as long as one outermost layer of the sheet is a thermoplastic resin layer, the other side of the sheet may be the base material exposed or may be laminated with the thermoplastic resin layer. When the thermoplastic resin layers are provided as both outermost layers of the sheet, these layers may be formed of different types and compositions of thermoplastic resins. The surface condition of the thermoplastic resin layer may be any surface condition from low gloss to high gloss. In addition, another layer such as another thermoplastic resin layer may be present between the base material and the outermost thermoplastic resin layer.

The present invention will be specifically described below.
[Thermoplastic resin layer]
<(A) Low density polyethylene>
Among the thermoplastic resin layers provided in the present invention, the outermost layer includes low-density polyethylene (LDPE) as the thermoplastic resin (A) and at least one thermoplastic resin (B) selected from a specific group described below. And are contained. The low density polyethylene may have a density of 0.85 to 0.92 g / cm ³ and a melt flow rate (MFR (JIS K6922-2)) of 3 to 20 g / 10 min. The manufacturing method is not questioned. The low density polyethylene is contained in an amount of 50% by weight or more based on the outermost thermoplastic resin layer, and if it is less than 50% by weight, sufficient substrate adhesion cannot be obtained. Preferably it is 60 weight% or more, More preferably, it is 70 weight% or more, More preferably, it is 80 weight% or more. Furthermore, although the ink drying property is slightly inferior, the result of satisfying the substrate adhesion can be obtained even at 100% by weight. Considering the ink drying property, the total content is preferably 90% by weight or less.

<(B) Specific thermoplastic resin>
As the thermoplastic resin contained together with the low density polyethylene, at least one selected from polyethylene resins, polypropylene resins, ethylene-acrylate copolymer resins, and styrene-butadiene copolymer resins is used. Some of these resins are inferior in substrate adhesion, but are improved by being formed as a mixed layer with the above-described low density polyethylene. In the present invention, the mixed layer composed of the above-described low-density polyethylene and these resins has a sea-island structure, and the ink is absorbed in the fine gaps between the resins, so that the ink drying property. It is thought to improve. In particular, linear low density polyethylene is preferably used because of its high ink absorption capability. The sea-island structure as used in the present invention refers to a structure in which a certain resin is distributed in a scattered manner so as to be surrounded by a different resin, such as the sea and islands floating in the sea. Say. However, the distribution of the “islands” relative to the “sea” does not necessarily have a dotted shape depending on the mixing ratio of the resin, and may be in a dense state.

The polyethylene-based resin is different from the low-density polyethylene of the resin (A) described above, has a density of 0.85 to 0.98 g / cm ³ , and a melt flow rate (MFR (JIS K6922-2)) of 3 Examples thereof include 20 g / 10 min linear low density polyethylene (LLDPE), low density polyethylene (LDPE), and high density polyethylene (HDPE). Production methods such as a high-pressure method, a catalyst method, a gas phase method, and a solution method are not limited. Among linear low-density polyethylenes, linear low-density polyethylene (SS-LLDPE) synthesized with a single-site catalyst is preferable. . Since SS-LLDPE is synthesized with a single-site catalyst having a uniform active site, it shows a sharp molecular weight distribution compared to linear low density polyethylene (LLDPE) synthesized using a Ziegler catalyst that is widely used. A typical example of the single site catalyst is a metallocene catalyst. This is a catalyst having a structure in which transition metal atoms such as titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum or tungsten are sandwiched between two cyclopentadiene rings.

The polypropylene resin preferably has a density of 0.85 to 0.93 g / cm ^{3 and a} melt flow rate (MFR (JIS K7210: 1999)) satisfying a condition of 15 to 50 g / 10 min. Any of a block copolymer type, a random copolymer type, and a metallocene catalyst method type can be suitably used.

  The ethylene-acrylate copolymer resin is preferably an ethylene-methyl acrylate copolymer resin (EMA), an ethylene-ethyl acrylate copolymer resin (EEA), or an ethylene-butyl acrylate copolymer resin, and more preferably each has a methyl acrylate content. It is preferable that the ethyl acrylate content and the butyl acrylate content be 5% or more. In addition, an ionomer resin in which molecules of an ethylene-methacrylic acid copolymer are cross-linked with metal ions can be used.

<Other resins>
In addition, the outermost layer has an aliphatic petroleum resin, an aromatic petroleum resin, a hydrogenated petroleum resin, a terpene petroleum resin, a hydrogenated terpene series as necessary, as long as the desired effect of the present invention is not impaired. Petroleum resins such as petroleum resins and copolymerized petroleum resins, ethylene / α-olefin copolymer resins, propylene / α-olefin copolymer resins and other α-olefin copolymer resins, ethylene / carboxylic acid vinyl ester copolymers Polymerized resins, ethylene / α, β-unsaturated carboxylic acid ester copolymer resins, high-pressure low-density polyethylene resins such as ordinary ionomer resins, polystyrene resins, polymethylpentene resins, and the like can be used. For example, by adding an adhesive resin to the resin blend, it is possible to produce a laminated sheet having a higher degree of substrate adhesion.
In addition, when two or more thermoplastic resins forming the outermost layer and the base material, or two or more thermoplastic resin layers are provided, if the adhesion between the resin layers is poor, an adhesive layer is applied or laminated on the base material in advance. It is also possible to coextrude and laminate the thermoplastic resin and adhesive resin used for the outermost layer or other layers.
Examples of the adhesive resin include, but are not limited to, acrylic resins, epoxy resins, modified polyolefins, and ionomers. As the modified polyolefin, a modified product obtained by graft-modifying a homopolymer or copolymer of an α-olefin having 2 to 20 carbon atoms with a monomer having a polar group and an ethylenic double bond can be used. It is not limited to. An ionomer is an ion-containing polymer, especially a polymer that is partially or completely neutralized by metal ions or quaternary ammonium, and is especially grafted with a small amount of (meth) acrylic acid on an ethylene polymer chain. A product obtained by neutralizing a part of the (meth) acrylic acid with Na +, K +, Zn ++, Mg ++ or the like can be preferably used. Of these, Zn is preferable because of good gloss.
Furthermore, in the present invention, a thermoplastic resin layer may be appropriately provided in addition to the above-described thermoplastic resin layer. The thermoplastic resin for forming such a layer is not particularly limited, and examples thereof include resins that can be laminated, such as polypropylene, polyethylene, polystyrene, polyethylene terephthalate, polybutylene terephthalate, and polymethylpentene.

[Additive]
Additives such as antistatic agents and antiblocking agents (acrylic beads, glass beads, silica) may be added to each thermoplastic resin layer as long as the object of the present invention is not impaired. In addition, inorganic fillers such as titanium oxide, calcium carbonate, talc, kaolin, barium sulfate, calcium silicate, magnesium carbonate, zinc oxide, magnesium oxide, silicon oxide, diatomaceous earth, magnetic iron oxide and mixtures thereof are mixed. If necessary, a small amount of organic filler such as carbon black, phenol resin, melamine resin, urea resin may be mixed, and fatty acid salt as an auxiliary means for improving the dispersibility of the inorganic filler, A tackifier, a hydrophilized polyolefin wax, or the like can be added as appropriate, or the surface treatment of the inorganic filler can be performed with these. The average particle size of the inorganic filler used is not particularly limited, but from the viewpoint of dispersibility in the resin layer and the writing property and printability that the inorganic filler imparts to the resin layer, it is 0.01 to 10 μm. Preferably, 0.1-5 micrometers is still more preferable.

[Base material]
As the base material used in the present invention, various kinds of thin and thick papers, synthetic resin films, metal foils, and the like can be used.

[Lamination method]
The laminated sheet of the present invention can be produced by laminating the above thermoplastic resin on a base material using a known method such as extrusion lamination, coextrusion lamination, dry lamination, wet lamination, or the like. As for the thickness of each resin layer, the outermost layer is preferably 2 to 25 μm, more preferably 5 μm to 20 μm. When the thermoplastic resin layer is composed of two or more layers, the layers other than the outermost layer are preferably 3 to 25 μm, more preferably 5 to 20 μm.
In addition, in order to improve adhesion to the substrate, the substrate surface before extrusion coating is subjected to flame (flame) treatment, corona discharge treatment, and pre-heat treatment, or in contact with the substrate of the resin layer to be laminated. It is desirable to perform treatment such as ozone treatment on the power surface. As a result, the low-temperature adhesiveness is improved, the frequency of occurrence of glazing from the resin is reduced, and deterioration of the resin and reduction in tear strength can be prevented.

[Ink receiving layer]
In the present invention, at least one surface of a laminated sheet or a sheet made of a thermoplastic resin having a thermoplastic resin layer as one or both outermost layers of the sheet-like base material, the primary particles are spherical as an ink receiving layer. The coating layer has an inorganic pigment selected from colloidal silica having a ratio of secondary particle diameter to primary particle diameter of 1.5 to 3.0, or acicular colloidal alumina and a binder as main components.

[Inorganic pigment]
<Colloidal silica>
In this invention, a primary particle is spherical and contains the colloidal silica whose ratio of the secondary particle diameter with respect to a primary particle diameter is 1.5-3.0. The primary particle size is 10 to 300 nm, more preferably 30 to 70 nm. The effect of the present invention is exhibited by performing offset printing on the sheet provided with the coating layer. By blending such inorganic pigments, fine voids are formed in the coating layer, making it easier to absorb the solvent of printing ink, but it does not diffusely reflect light like pigments such as kaolin, talc, silica, etc. Can be obtained. In addition, such inorganic pigments have higher binding properties to binders than common pigments such as titanium oxide, calcium carbonate, clay, talc, silica, etc., and when blended in the coating layer, they drop from the thermoplastic resin and have surface strength. Therefore, the ratio of the inorganic pigment can be increased, and excellent blocking resistance can be obtained together.
Therefore, the water-resistant sheet of the present invention can promptly advance the process after printing without causing troubles such as backing during printing, and the printing press can be stably operated. Further, in the present invention, since the particle size of the inorganic pigment is small, the surface of the coating layer is excellent in flatness, and high gloss can be obtained as compared with the case where a general inorganic pigment is blended.

However, when the primary particle diameter of the inorganic pigment is smaller than 10 nm, it is difficult to form fine voids in the coating layer, which is not preferable. On the other hand, when the primary particle diameter exceeds 300 nm, light is likely to be scattered, and it becomes difficult to obtain excellent glossiness.
In general, a water-resistant sheet such as a laminated sheet having a thermoplastic resin layer as one or both outermost layers of the sheet or a sheet made of a thermoplastic resin has an unstable behavior with respect to dampening water at the time of offset printing. The remaining water is often a problem. In contrast, by using an inorganic pigment in which spherical primary particles form secondary particles by bonding or agglomeration as such an inorganic pigment, it is possible to make it less likely to cause excess water. This is because, compared with the case of using an inorganic pigment that does not form secondary particles, the particles are less likely to be densely arranged and the coating layer has more voids, and the dampening water is more easily absorbed by the coating layer. This is thought to be because the absorption capacity of dampening water is further increased. As a result, it is considered that the transfer of ink from the blanket is not inhibited.

  In this invention, it is preferable in the ratio with respect to the primary particle diameter of the said secondary particle being 1.5-3.0. When the ratio is smaller than 1.5, the shapes of the primary particles and the secondary particles do not change so much and it becomes difficult to form voids in the coating layer for absorbing the fountain solution. On the other hand, if it exceeds 3.0, it becomes difficult to obtain the gloss of the coating layer, more preferably 2.5 or less. In the present invention, the primary particle size and secondary particle size of colloidal silica can be measured by the BET method, the dynamic light scattering method, or the like.

  The colloidal silica in the present invention is usually observed in a dispersed state with a microscope, and a large number of two or three spherical single colloidal silica (primary particles) are observed. For convenience, this is expressed as a peanut shape. The average value of the number of connected primary particles is substantially proportional to the above ratio. The colloidal silica in the present invention is a chain-like (also referred to as a pearl necklace) colloidal silica (when observed with a microscope, at least 5 spherical single colloidal silicas, usually 10 or more continuous, the above ratio is also 5 This is not included. The term “not included” does not mean that no chain colloidal silica is observed at the time of microscopic observation, but some tufted colloidal silica may be observed, but the primary physical property is macroscopic. A value obtained by measuring a ratio of the secondary particle diameter to the particle diameter exceeds 3.0 (usually 5 or more). The colloidal silica used in the present invention is synthesized by sol-gel method using alkoxysilane as a raw material, and the primary particle size (BET method particle size) and secondary particle size (dynamic light scattering method particle size) are controlled by the synthesis conditions. It is preferable to do so. As such colloidal silica, trade name Quatron manufactured by Fuso Chemical Industry Co., Ltd. can be mentioned. In addition, as the colloidal silica of the present invention, the aggregate in which primary particles are aggregated is subdivided into secondary particles having an average particle diameter of about 10 nm to several 100 nm by mechanical means (excluding dry pulverization). It does not contain colloidal particles.

<Acicular colloidal alumina>
The acicular colloidal alumina is one in which acicular primary particles form secondary particles by bonding or agglomeration, and exhibits the same effects as the colloidal silica described above. The primary particle diameter has a longest diameter of 10 to 20 nm and a secondary particle diameter of about 20 to 30 nm.

<Other inorganic pigments>
As long as the desired effect is not impaired in the present invention, it may contain conventionally known inorganic pigments and plastic pigments such as titanium oxide, calcium carbonate, clay, talc, kaolin, calcined kaolin, and silica in addition to the above inorganic pigments. it can.

[binder]
The binder preferably has water resistance, adhesiveness to the surface of the thermoplastic resin layer or the thermoplastic resin sheet, adhesiveness to the offset ink, holding power of the inorganic pigment contained in the coating layer, etc. Can be selected and used as appropriate. For example, a polymer or copolymer such as ethylene, propylene, butadiene, (meth) acrylic acid, vinyl acetate, vinyl chloride, styrene, or a modified product thereof, or a mixture of these with a urethane resin or an epoxy resin. Among them, styrene, butadiene, (meth) acrylic polymers or copolymers thereof are preferable. In the present invention, water-soluble binders such as polyvinyl alcohol tend to have poor water resistance compared to styrene, butadiene, (meth) acrylic polymers or copolymers thereof. However, the water resistance can be improved when used in combination with the above water-resistant binder as long as the desired effect is not impaired.

[Formation method]
The blending amount of the inorganic pigment in the coating liquid is preferably 10 to 500% by weight with respect to the binder. When the blending amount is less than 10% by weight, voids are not easily formed in the formed coating layer, and the effect of imparting ink absorption ability cannot be exhibited. When the blending amount exceeds 500% by weight, the surface strength and thermoplasticity of the coating layer are not achieved. Desorption from the resin surface is likely to occur. In addition to the above inorganic pigments, conventionally known inorganic / organic fillers such as titanium oxide, calcium carbonate, clay, talc, kaolin, calcined kaolin, and silica can be blended as long as the desired effect is not impaired. However, when emphasizing the glossiness of the sheet, it is desirable not to add such a filler or to keep it to a minimum amount.
Coating of the coating liquid onto the surface of the thermoplastic resin layer or the surface of the thermoplastic resin sheet can be performed by a conventional method using an air knife coater, blade coater, roll coater, curtain coater, gravure coater, die coater or the like. The coating amount is preferably 0.5 to 10 g / m ² (dry weight, the same shall apply hereinafter). When the coating amount is less than 0.5 g / m ² , the effect of the above-described inorganic pigment, that is, the effect of imparting ink absorption ability cannot be exhibited. On the other hand, if it exceeds 10 g / m ² , it is not economically preferable because the drying load increases. Coating amount in the range of 0.5 to 10 g / ^{m 2,} especially in the case where the range of 1-8 g / ^{m 2,} it is possible to sufficiently avoid such problems. Although the water-resistant sheet of the present invention can be printed using generally used ink, the coating layer (ink receiving layer) on the sheet surface can be made as thin as 10 g / m ² or less. Therefore, the strength of the coating layer can be secured, and the productivity and economy are excellent.
In addition to the above, various commonly used additives can be added to the coating layer. Examples of these additives include antistatic agents, white pigments (inorganic pigments such as titanium oxide, calcium carbonate, clay, talc, and silica), anti-blocking agents (acrylic beads, glass beads, silica, and the like), and the like. .

〔Example〕
EXAMPLES Examples and comparative examples of the present invention will be described below, but it goes without saying that the present invention is not limited to these examples. Unless otherwise specified, parts and% represent parts by weight and% by weight. Table 1 shows Examples 1 to 15 and Comparative Examples 1 to 20 including the resin composition and coating layer composition used in Examples and Comparative Examples. Moreover, quality was evaluated about the laminated sheet obtained by the Example and the comparative example. In some cases, lithographic offset printing is performed, and the drying property after printing with normal dampening water amount and the ink transfer property when printing with excessive dampening water amount (normal double amount) are evaluated. did. For printing, an ink for offset printing (“Values-G” manufactured by Dainippon Ink Co., Ltd.), which is widely used for coated paper, was used.

<Physical properties and properties>
Low density polyethylene (LDPE): MFR (JIS K6922-2) 7.5 g / 10 min, density 0.918 g / cm ³
Linear low density polyethylene (LLDPE): MFR (JIS K6922-2) 20 g / 10 min, density 0.888 g / cm ³
High density polyethylene (HDPE): MFR (JIS K6922-2) 17 g / 10 min, density 0.967 g / cm ³
Polypropylene (PP): MFR (JIS K7210: 1999) 24 g / 10 min, density 0.91 g / cm ³
Ethylene / methyl acrylate copolymer (EMA): MFR (JIS K7210: 1999) 6.0 g / 10 min, density 0.930 g / cm ³
Ethylene / ethyl acrylate copolymer (EEA): MFR (JIS K6730) 5.0 g / 10 min, ethyl acrylate (EA) content 25%
Styrene-butadiene copolymer (SBR): MFR (ASTM D297) 3.5 g / 10 min, density 0.89 g / cm ³
Ethylene / α-olefin copolymer: MFR 3.6 g / 10 min, density 0.88 g / cm ³ , JIS-A surface hardness 83
(In Table 1, the above-mentioned “()” notation is used for the resin name.)

<Base material adhesion>
A transparent adhesive tape made by Nichiban Co., Ltd. (trade name cello tape (registered trademark)) was firmly adhered to the surface of the thermoplastic resin layer, and the transparent adhesive tape was forcibly peeled off and evaluated visually according to the following criteria. .
5: Nothing adheres to the tape adhesive surface, and the thermoplastic resin layer does not peel from the substrate layer at all. Or although the whole base material is destroyed, it has not peeled at all between the thermoplastic resin layer and the base material.
4: The thermoplastic resin has adhered slightly to the tape adhesive surface. Alternatively, the base material is broken, but peeling occurs partially between the thermoplastic resin layer and the base material.
3: The thermoplastic resin adheres to about half the area of the tape adhesive surface, the base material does not break down, and it peels between the base material and the thermoplastic resin layer.
2: Thermoplastic resin adheres to almost the entire surface of the tape adhesive surface, and there is resistance when the tape is peeled off.
1: Thermoplastic resin adheres to almost the entire surface of the tape adhesive surface, and there is almost no resistance when the tape is peeled off.

  Further, lithographic offset printing was performed, and the drying property after printing when printing with a normal amount of dampening water and the ink transferability when printing with an excessive amount of dampening water (twice the normal amount) were evaluated. In addition, printing used the offset printing ink ("Values-G" by Dainippon Ink Co., Ltd.) which is widely used for coated paper. The results are shown in Table 1.

[Glossiness]
The glossiness of white paper was measured using a 75 ° gloss meter (GM-26PRO manufactured by Murakami Color Research Laboratory Co., Ltd.). The higher the glossiness is, the better the beauty is, and when it is 30% or more, the glossiness is particularly good.

[Blocking resistance]
A blank paper sample was cut into a size of 5 cm × 10 cm, the two sheets were overlapped with each other and a 6 kg weight was placed on the coated surface so that the load was evenly applied to the sample, and held for 1 week in an environment of 40 ° and 85% RH. Then, the adhesion state when the sample was peeled off was evaluated.
○: There is no resistance when peeled off.
Δ: Slightly blocked, but no change is observed in the surface state of the sample.
X: Blocking, and the surface state is changed, such as missing coating layer.

[Ink drying after printing]
After printing, the sheet was held so that it did not come into contact with air. After a certain period of time, the solid portion was overlaid with general A2 coated paper, and the time until ink was not transferred to the coated paper when a certain load was applied was measured. The shorter the time, the better the drying properties. The unit is “time”.

[Ink transferability with excessive amount of dampening water]
The transferability of the ink when printed was visually evaluated.
○: Printing unevenness is not seen, and excellent printing finish is achieved.
Δ: Printing unevenness is observed, and portions where ink is not transferred are observed in some places.
X: Ink has not transferred.

[water resistant]
After printing and drying the ink sufficiently, the solid part was applied to water, and the degree of ink peeling when rubbed strongly with a finger was visually evaluated.
○: Ink does not peel ×: Ink peels

[Particle size measurement of colloidal silica]
The primary particle size was determined by calculating the specific surface area by the nitrogen adsorption method and calculating from the following formula. The secondary particle size was measured with a Coulter N4 meter (trade name, manufactured by Coulter), and the number average value was used as the particle size.

[Examples and Comparative Examples]
Hereinafter, the present invention will be described based on examples. Unless otherwise specified, parts and% indicate parts by weight and% by weight.

Pre-melted low density polyethylene (LDPE: MFR 7.5 g / 10 min, density 0.918 g / cm ³ ) was applied to both sides of a fine paper with a basis weight of 81 g / m ² at an extrusion temperature of 290 ° C. using a T-die. Extrusion lamination was performed, and a laminated sheet was prepared by pressure bonding with a mirror-like cooling roll, and then corona discharge treatment was performed on both sides of the laminated sheet. In addition, the thickness of the polyethylene layer laminated | stacked on both surfaces of the lamination sheet at this time was 20 micrometers, respectively.
On the other hand, an aqueous dispersion of styrene-acrylic copolymer (shown as “StAC” in Table 1) (concentration 40%, average particle size 0.19 μm) and 150 parts by weight of peanuts having an average primary particle size of 23 nm and a secondary particle size of 50 nm 300 parts by weight of colloidal silica (shown as “PL-2” in Table 1) (trade name: PL-2, manufactured by Fuso Chemical Industry Co., Ltd.) was mixed to prepare a coating solution. This coating solution was applied to both surfaces of the laminated sheet using a Mayer bar so that the solid content was 3 g / m ² to obtain a water-resistant sheet.

(Examples 2-15, Comparative Examples 1-17)
As shown in Table 1, a water-resistant sheet was obtained in the same manner as in Example 1 except that the type of resin and its composition or the type of binder or pigment in the coating layer and its composition were changed.
(Comparative Examples 18-20)
Comparative Examples 18 to 20 are comparative examples in which no coating layer is provided.

Abbreviations in Table 1 other than those described in other places are as follows: Binder AC: Acrylic polymer Compound pigment PL-7: Peanut-like colloidal silica Compound pigment PL-20: Peanut-like colloidal silica Formulation pigment HP-14: Acicular colloidal alumina Formulation pigment ST-20: Spherical colloidal silica Formulation pigment X-37B: Synthetic silica

As is clear from Examples 1 to 15, peanut-shaped colloidal silica or needle-shaped resin containing 50% by weight or more of low-density polyethylene as resin A and further forming secondary particles as an inorganic pigment to be blended in the coating layer. The laminated sheet of the present invention using colloidal alumina exhibits a quality that satisfies both the substrate adhesion and the ink drying property. Further, even when a large amount of dampening water is used, the ink transfer is suppressed, and the quality balance is further improved. It became excellent.
It was confirmed that when the LDPE was 50 to 90% by weight as the resin A, the ink drying property could be halved to 0.5 hours or less as compared with 100% by weight of LDPE.
Example 6 using PVA as a binder for the coating layer is excellent in substrate adhesion, ink drying properties, etc., although having poor water resistance, and has sufficient effects for indoor posters.
Moreover, when the low density polyethylene mix | blended as the resin A is less than 50 weight part (Comparative Examples 1-12, Comparative Example 14), it is inferior to either or both of base-material adhesiveness and ink drying property, and has a good balance quality. No laminated sheet was obtained. The same was true when a resin different from the specific thermoplastic resin group selected as the resin B of the present invention was used (Comparative Example 13).
Furthermore, in Comparative Examples 18 to 20 in which no coating layer is provided and in Comparative Example 17 in which no pigment is contained in the coating layer, both are inferior in ink drying properties, and Comparative Example 15 (secondary) using a general pigment Spherical colloidal silica that does not form particles) was inferior in ink transfer, and Comparative Example 16 (synthetic silica) was inferior in gloss.

Claims (4)

In the water-resistant laminated sheet in which the coating layer is formed on the laminated sheet having the thermoplastic resin layer,
A laminated sheet having a thermoplastic resin layer is a laminated sheet in which one or more thermoplastic resin layers are laminated on one or both surfaces of a sheet-like substrate, and the outermost layer of the thermoplastic resin layer is the following resin. (A) and a thermoplastic resin obtained by mixing at least one selected from the group (B), and contains 50% by weight or more of the thermoplastic resin of the following resin (A),
The coating layer is a coating layer mainly composed of an inorganic pigment and a binder on at least one surface of the thermoplastic resin layer of the laminated sheet, and the primary particles are spherical and the primary particles as the inorganic pigment. A water-resistant laminated sheet comprising colloidal silica having a ratio of secondary particle diameter to diameter of 1.5 to 3.0 or acicular colloidal alumina.
(A) Low density polyethylene having a density of 0.85 to 0.92 g / cm ³ and a melt flow rate (MFR (JIS K6922-2)) of 3 to 20 g / 10 min. (B) Polyethylene resin, polypropylene resin, ethylene Acrylate copolymer resin, styrene-butadiene copolymer resin   The water-resistant laminated sheet according to claim 1, wherein the thermoplastic resin of the resin (A) is contained in an amount of 50 to 90% by weight.   The thermoplastic resin (B) is linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene (PP), ethylene / methyl acrylate copolymer (EMA), ethylene / ethyl acrylate copolymer (EEA). ) Or a styrene-butadiene copolymer (SBR). The water-resistant laminated sheet according to claim 1 or 2.   The water-resistant laminated sheet according to any one of claims 1 to 3, wherein the binder of the coating layer is at least one selected from a styrene, butadiene, (meth) acrylic acid polymer or copolymer.