CA2153182C - Coated printing paper - Google Patents
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- CA2153182C CA2153182C CA 2153182 CA2153182A CA2153182C CA 2153182 C CA2153182 C CA 2153182C CA 2153182 CA2153182 CA 2153182 CA 2153182 A CA2153182 A CA 2153182A CA 2153182 C CA2153182 C CA 2153182C
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- surface layer
- copolymer
- pigment
- thermoplastic polymer
- paper
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H19/00—Coated paper; Coating material
- D21H19/80—Paper comprising more than one coating
- D21H19/82—Paper comprising more than one coating superposed
- D21H19/822—Paper comprising more than one coating superposed two superposed coatings, both being pigmented
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H19/00—Coated paper; Coating material
- D21H19/36—Coatings with pigments
- D21H19/38—Coatings with pigments characterised by the pigments
- D21H19/42—Coatings with pigments characterised by the pigments at least partly organic
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Abstract
In a coated printing paper having a pigment-containing layer on at least one of a substrate, a surface layer containing thermoplastic polymer latex particles having an average particle diameter of less than 100 nm and a secondary transition temperature of higher than 80°C is provided on the pigment containing layer, and the surface layer is not necessarily calendered. The coated printing paper has a practically sufficient printing adaptability, a high gloss, and a constant quality.
Description
Coated Printing Paper FIELD OF THE INVENTION
The present invention relates to a high-gloss coated paper with improved printability.
BACKGROUND OF THE INVENTION
Coated paper having a coating layer comprising a pigment and a binder is used as a high-grade printing paper, for which the gloss of the coating layer surface is important in addition to printing adaptability such as ink absorptivity and strength of the coating layer. When the coating layer surface is smoothened by applying a pressure to enhance the gloss, voids of the coating layer are collapsed to decrease the ink absorptivity. Further, when large amounts of a water-soluble or water-dispersible polymer substance such as polymer latex used as the binder for the pigment are added, the coating layer strength and the gloss are improved, but voids of the coating layer are reduced to decrease the ink absorptivity. Thus, the gloss and the printing adaptability conflict with each other. In coated paper, types and composition of the pigment and adhesive, coating amount of the coating color, degree of smoothing, and the like are determined so that the gloss and the printing adaptability are well balanced. However, to obtain high gloss paper with good printing adaptability, another technology is required. Coated printing paper generally includes slightly coated paper, coated paper, art paper, superart paper, and cast coated paper in the increasing order of gloss. High gloss in the present ;,~ CA2153182 invention means a gloss equal to or higher than superart paper. Therefore, high gloss paper means a coated printing paper having a gloss higher than superart paper.
For the production of high gloss paper, a cast coater method has heretofore been used. In this method, wet coating layer comprising pigments and binders is pressed against a mirror-finished cast drum, and heated to dry, and the method is substantially slower in production speed than conventional art paper, coated paper, or slightly coated paper.
Further, a method using a heated calender, rather than the cast drum, is known. For example, Japanese Patent Laid-open Publication (OPI) 56-68188, and Japanese Patent Publications 64-10638 and 64-11758 disclose methods in which a mixture of a pigment and a polymer latex or a water-soluble resin is coated and dried, and the coating layer is treated by a heated calendar. In these methods, a substrate is coated thereon with a polymer latex having a glass transition temperature of 5°C or higher than 38°C, and the coating layer is treated by a heated calendar of which the heating temperature is set so that the temperature of the coating layer becomes higher than the glass transition temperature of the latex used. This method is simple, good in productivity, and is thus suitable for the production of general coated paper, but is insufficient in terms of gloss, cannot provide a gloss higher than cast coated paper or superart paper, and cannot obtain a gloss comparable to that of cast coated paper.
Another method is disclosed in Japanese OPI
The present invention relates to a high-gloss coated paper with improved printability.
BACKGROUND OF THE INVENTION
Coated paper having a coating layer comprising a pigment and a binder is used as a high-grade printing paper, for which the gloss of the coating layer surface is important in addition to printing adaptability such as ink absorptivity and strength of the coating layer. When the coating layer surface is smoothened by applying a pressure to enhance the gloss, voids of the coating layer are collapsed to decrease the ink absorptivity. Further, when large amounts of a water-soluble or water-dispersible polymer substance such as polymer latex used as the binder for the pigment are added, the coating layer strength and the gloss are improved, but voids of the coating layer are reduced to decrease the ink absorptivity. Thus, the gloss and the printing adaptability conflict with each other. In coated paper, types and composition of the pigment and adhesive, coating amount of the coating color, degree of smoothing, and the like are determined so that the gloss and the printing adaptability are well balanced. However, to obtain high gloss paper with good printing adaptability, another technology is required. Coated printing paper generally includes slightly coated paper, coated paper, art paper, superart paper, and cast coated paper in the increasing order of gloss. High gloss in the present ;,~ CA2153182 invention means a gloss equal to or higher than superart paper. Therefore, high gloss paper means a coated printing paper having a gloss higher than superart paper.
For the production of high gloss paper, a cast coater method has heretofore been used. In this method, wet coating layer comprising pigments and binders is pressed against a mirror-finished cast drum, and heated to dry, and the method is substantially slower in production speed than conventional art paper, coated paper, or slightly coated paper.
Further, a method using a heated calender, rather than the cast drum, is known. For example, Japanese Patent Laid-open Publication (OPI) 56-68188, and Japanese Patent Publications 64-10638 and 64-11758 disclose methods in which a mixture of a pigment and a polymer latex or a water-soluble resin is coated and dried, and the coating layer is treated by a heated calendar. In these methods, a substrate is coated thereon with a polymer latex having a glass transition temperature of 5°C or higher than 38°C, and the coating layer is treated by a heated calendar of which the heating temperature is set so that the temperature of the coating layer becomes higher than the glass transition temperature of the latex used. This method is simple, good in productivity, and is thus suitable for the production of general coated paper, but is insufficient in terms of gloss, cannot provide a gloss higher than cast coated paper or superart paper, and cannot obtain a gloss comparable to that of cast coated paper.
Another method is disclosed in Japanese OPI
:, 71142-44 ~;~~15318?_ 59-22683. This method is a technology in which a sheet alone or a sheet having a pigment coating layer is coated thereon with a mixture of two or more polymer latices differing in the minimum film-forming temperatures, dried, and flattened by a calender as necessary. Hy coating latices with different minimum film-forming temperatures in combination and drying, fine cracks are generated on the surface of the coated paper, thereby improving the ink absorptivity without impairing the gloss. In this technology, it is important to generate fine cracks on the surface of the coated paper. For this purpose, the drying condition must be carefully controlled. That is, the drying condition must be set so that the latex of lower minimum film-forming temperature completely melts, whereas the latex of higher minimum film-forming temperature partly melts.
However, as well known, the drying condition generally tends to be varied according to various factors. In considering industrial application of this technology, it is practically impossible to maintain the drying condition always uniform and constant over the entire production process. Therefore, it is extremely difficult to maintain a constant, stable quality.
In view of the above situation, an object of the present invention is to provide a coated printing paper which has a practically sufficient printing adaptability and a high gloss, and a production method of a coated printing paper which is able to assure a constant quality easily and at a low cost.
However, as well known, the drying condition generally tends to be varied according to various factors. In considering industrial application of this technology, it is practically impossible to maintain the drying condition always uniform and constant over the entire production process. Therefore, it is extremely difficult to maintain a constant, stable quality.
In view of the above situation, an object of the present invention is to provide a coated printing paper which has a practically sufficient printing adaptability and a high gloss, and a production method of a coated printing paper which is able to assure a constant quality easily and at a low cost.
C~215~182 SUMMARY OF THE INVENTION
The inventors have previously proposed, in Japanese Patent Unexamined Publication No. 3-167396, a method in which a base material comprising a substrate coated thereon with a pigment coating layer is coated on the pigment coating layer with a surface layer comprising a thermoplastic polymer latex having a secondary transition temperature of higher than 80°C, and the surface layer is calendered at a temperature below the secondary transition temperature. After that, having conducted studies, the inventors have found that the above object is attained by using a thermoplastic polymer latex having a very small particle diameter, without necessarily requiring a calender treatment. Therefore, the present invention provides a coated printing paper having as pigment containing layer on at least one side of a substrate, characterized in that a surface layer containing thermoplastic polymer latex particles having an average particle diameter of less than 100 nm and having a secondary transition temperature of higher than 80°C is provided on the pigment containing layer, and the surface layer is not necessarily calendered.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an electron microscopic photograph of a surface layer of a coated printing paper according to a preferred embodiment of the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
In general, as the printing base material, paper, synthetic paper, plastic films, non-woven fabrics, and the like are used, and of these materials, paper is the most commonly used. The paper includes pigment coated papers such as art paper, coated paper, slightly coated paper, and coated white board, and uncoated papers such as fine paper, medium grade paper, newsprint paper, one side glazed paper, and special gravure paper.
In the present invention, the base material used for achieving both high gloss and printing adaptability must be, among the above printing base materials, one which is provided with a pigment containing layer on the substrate. The substrate may be one which can be provided thereon with the pigment containing layer, is not specifically limited, and an uncoated paper such as medium grade paper or fine paper is preferable. Formation of the pigment containing layer on the uncoated paper is sufficiently achieved by a production method of conventional pigment coated paper, in which types of the pigment and binder in the coating color and the ratio of the pigment and the binder are appropriately controlled according to the desired quality. The pigment coated paper is a one- or two-sided paper of a coating weight of the coating layer of 2 to 40 g/m2 per one side. After pigment coating, a thermoplastic polymer latex is coated on the pigment coating layer to form a surface layer. However, the pigment coating layer may be smoothened by a supercalender or a gloss calender before top coating. When the thermoplastic polymer latex containing layer is formed directly on the uncoated paper without providing a pigment containing layer, printing a adaptability is ensured, but a high gloss as expected cannot be obtained.
Further, when a synthetic paper or plastic film is used as a substrate, and the thermoplastic polymer latex layer is formed directly on the substrate without proving a pigment containing layer, a desirable gloss can be obtained, but dryability of ink is insufficient and no printing adaptability is obtained. The thermoplastic polymer latex used in the present invention is an emulsion of a polymer or copolymer having a thermoplasticity, having a secondary transition temperature of higher than 80°C and an average particle diameter of less than 100 nm (hereinafter an emulsion of a polymer or copolymer having a thermoplasticity is simply referred to "polymer latex"). For core-shell type latex, the secondary transition temperature of the shell portion must be higher than 80°C. Type and production method of the monomer constituting the polymer latex are not specifically limited if the secondary transition temperature is higher than 80oC.
Preferable monomers include styrene and its derivative, vinylidene chloride, acrylic or methacrylic esters.
Upper limit of the secondary transition temperature of the polymer latex is not specifically limited. It is mainly determined by the types of the monomer and the plasticizes in the production of the polymer latex, and is normally about 130°C.
When a polymer latex of a secondary transition temperature of below 80oC is used, the paper tends to adhere to the calender roll during calendering, the resulting coated paper is insufficient in gloss, weak in the pick strength of the surface layer, no printing adaptability is obtained, and the object of the present invention is not attained.
In general, the particle diameter of latices used in paper coating application is smaller than that for other applications such as paint, and is mainly an average particle diameter of about 200 nm to 1,000 nm. However, the polymer latex of the present invention has an even smaller average particle diameter of less than 100 nm. Hy using a latex less than 100 nm in average particle diameter, a high gloss can be obtained without special smoothing treatment, which is comparable to that of general coated paper smoothened by a gloss calender or supercalender. However, if the coating layer of the polymer latex of the present invention is smoothened, a printing paper of very high gloss can be obtained. The smoothing treatment can be achieved by a supercalender or gloss calender used for treatment of general coated paper, which may be used in combination. However, the calendering condition is important, which must be at a temperature lower than the secondary transition temperature of the polymer latex used in the surface layer. The calendering temperature is not specifically limited if it is below the secondary transition temperature, and the temperature of more than 5oC lower, preferably 10 to 30oC lower than the secondary transition temperature of the polymer latex. If the treatment temperature is higher than the secondary transition temperature of the polymer latex used, the latex melts to form a film, the ink acceptability is extremely decreased, and the _ 7 _ ~, 71142-44 object of the present invention is not attained. Further, when the polymer latex begins to melt, the coating layer increases in stickiness, the coating layer tends to stick to the calender roll, and the smoothing treatment becomes impossible.
Therefore, it is desirable to add an appropriate amount of a lubricant to the polymer latex used according to the present invention. In general, a type of lubricant which is used as an external lubricant, among those used in plastic molding, is suitable for the present invention. As the external lubricants, those which are described in page 945 and after of "Handbook of Plastic and Rubber Additives, Revised and Enlarged Edition" (published by Kagakukogyosha, July 1989) are used. For the present invention, one or more lubricants selected from stearic acid and its derivatives, olelC acid and its derivatives, and polyethylene wax emulsion are preferably used alone or in combination. The content of the lubricants is determined from types of the lubricants and the polymer latex of the present invention, condition and degree of smoothing treatment, amounts and types of other additives, and the like. In the present invention, the lubricant is preferably used in an amount of about 5 to 40% by weight, more preferably 10 to 25% by weight, of the surface layer coating color containing the polymer latex particles of the present invention.
The polymer latex of the present invention is normally coated alone on the pigment coating layer. However, in additlon to the lubricants, plastic pigments, natural or _ g _ A
synthetic resin binders, flow modifiers and deformers, coloring agents, inorganic white pigments, and like may be appropriately added as far as the object of the present invention is not impaired, to obtain the surface layer coating color.
The plastic pigment used in the present invention is synthetic polymer particles mainly comprising polystyrene having an average particle diameter of more than 100 nm, including a type which has no substantial binding power in itself, and a type which has some binding power. An example of the former is hollow plastic pigment Rohpaque OP84 of Rohm & Haas Co., and an example of the latter in Nipol LX407HP of Nippon Zeon. When these plastic pigments are used in combination with the polymer latex of the present invention, it is appropriate to add the plastic pigment in an amount of less than 60~ by weight, preferably 20 to 40~ by weight, to the polymer latex of the present invention. Using the plastic pigment, the gloss and surface strength can be controlled.
The present invention basically does not use a so called binder. However, a small amount of a natural or synthetic resin binder for general-purpose coating may be used in order to adjust the surface strength of the coating layer, but the amount should be to an extent that the surface does not have a stickiness. Types of additives such as follow modifiers, defoamers, coloring agents, and inorganic white pigments of the coating color are those used in general paper, and the amounts thereof should be to an extent that generation of gloss and surface strength is not impaired.
_ g _ * Trade Mark 71142-44 y LA~1531 E2 The thus obtained surface layer coating color is coated on the pigment coating layer to form the surface layer.
The coating amount can be appropriately controlled so that the desired properties are obtained but, if the coating amount is excessive, not only the cost is increased, but also the ink absorptivity decreases. This results in insufficient ink set, and the surface strength is decreased. Therefore, an excessively large coating amount is not desirable, and normally a coating weight of more than 0.1 g/m2 per one side, preferably 0.3 to 3 g/m2 is sufficient.
Coating of the surface layer coating color is achieved by a blade coater, a roll coater, an air knife coater, a bar coater, a gravure coater, a flexographic coater, and the like which are normally used in the field of paper coating. Drying after coating does nat require a special condition when the polymer latex of the present invention is used, and an optimum surface layer can be obtained by a drying condition used in the production of ordinary coated paper.
For example, even in drying by hot air at 150°C, the temperature of the surface layer is as high as 80°C, and when the secondary transition temperature of the polymer latex of the present invention is higher than 80oC, the latex will never melt to form a film.
The reason why the coated printing paper of the present invention is practically sufficient in printing adaptability and has a high gloss has yet to be elucidated, but is presumed from observation by an electron microscope of the surface gloss layer of the coated paper obtained by the present invention as follows.
As can be seen from Fig. 1 the surface layer is not a continuous uniform film of molten polymer latex, but polymer latex particles of several tens of nm are closely arranged.
This is because the polymer latex used according to the present invention has a high secondary transition temperature of higher than 80°C, which does not melt under normal drying condition and maintains the shape of the polymer particles and, after calendering as necessary, the latex particles do not melt to form a continuous film, but fixes remaining the particle shape, as far as the temperature of the surface layer is lower than the secondary transition temperature of the polymer latex. As a result, there are a number of voids between particles of the polymer latex, thereby the printing ink is maintained between the voids, passes through capillaries between particles, penetrates to the pigment coating layer to be absorbed.
According to a known theory, the latex unmelted and maintaining the particle shape as shown in Fig. 1 should have no strength as a film, but the surface gloss layer of the present invention has a practically sufficient surface strength. The reason therefor is unknown at present, but it is considered that the polymer latex of the present invention having a secondary transition temperature of higher than 80oC
has some hardness during calendering, when such a latex is coated on the pigment coating layer and calendered, probably due to physical properties of the polymer latex determined by properties such as density and elasticity of the pigment "''~' coating layer, and chemical affinity between latices.
Further, from the common sense that a possibly uniform continuous surface is required to obtain a high gloss, it is cont racy to the expectation and is surprising that a high gloss is obtained despite that the coating layer surface of the polymer latex of the present invention maintains the particle shape. Possibly, this is presumed as due to the fact that the particle diameter of the polymer latex is small, the polymer latex mainly fills recesses of the pigment coating layer, and the surface layer is optically smoothened as a whole.
However, from the fact that the surface layer condition of the coated printing paper, which will be described later, maintains the particle shape of the polymer latex as in Fig. 1, it is strongly hypothesized that another factor is related to the function of providing the effect of the present invention, but which has yet to be elucidated.
Further, in the production of the coated printing paper, since the drying condition and calendering condition are unchanged from those of ordinary coated paper, a constant quality can be obtained without impairing the productivity.
DETAILED DESCRIPTION OF PREFERRED EXAMPLES
The present invention will be described in detail with reference to the Examples. However, the present invention is not limited to the Examples. Part and % used in the Examples, unless otherwise noted, indicate part by weight and % by weight, respectively.
CA21~3182 Production of the polymer latex Production Example 1 In a four-necked flask having a stirrer, a thermometer, a condenser, a dropping funnel, and a nitrogen gas introduction tube, 300 parts of water, 9 parts of sodium dodecylbenzenesulfonate, and 4 parts of polyoxyethylene-phenolether (10 mole of ethyleneoxide added) were placed, mixed with 60 parts of a monomer mixture of 80 parts of styrene, 10 parts of a-methylstyrene, 100 parts of methyl methacrylate, and 10 parts methacrylic acid, the temperature was increased to 60oC under nitrogen purging, mixed with 7.2 parts of 20% aqueous ammonium persulfate solution and 4.8 parts of 20% aqueous sodium bisulfite solution, and polymerized for 60 minutes. After 10 parts of 20% aqueous ammonium persulfate solution was added, the remnant 140 parts of the monomer mixture was added dropwise over a period of 1 hour. The reaction mixture was maintained at 90°C for 4 hours to complete polymerization to obtain an ethylenic monomer copolymer latex (A) having a secondary transition temperature of 107°C, an average particle diameter of 75 nm, and a solid content of 39%.
Production Exam le 2 In a four-necked flask having a stirrer, a thermometer, a condenser and a nitrogen gas introduction tube, 310 parts of water, 5.6 parts of HITENOL N-68 (polyoxyethylene nonylphenylether sulfate ester salt, Daiichi Kogyo Seiyaku), 48 parts of styrene, 19 parts of methyl methacrylate, 8 parts of ethyl methacrylate, 2.5 parts of * Trade Mark 71142-44 divinylbenzene, and 2.5 parts of methacrylic acid were placed.
The temperature was increased to 70oC under nitrogen purging, mixed with 5 parts of 16~ aqueous ammonium persulfate solution, maintained at 85oC for 4 hours to complete polymerization to obtain an ethylenic monomer copolymer latex (H) having a secondary transition temperature of 85oC, an average particle diameter of 75 nm, and a solid content of 21.2%.
Production Example 3 The same procedure as Production Example 1 was used, except that the monomers were replaced with 88 parts of styrene, 38 parts of methyl methacrylate, 70 parts of n-butyl methacrylate, and 4 parts of methacrylic acid, to obtain a copolymer latex (C) having a secondary transition temperature of 68°C, an average particle diameter of 70 nm, and a solid content of 39~.
Production of base material ( iament coated paper) A 64% solid coating color for coated paper comprising 70 parts of US NO.1 kaolin, 30 parts of fine particle ground calcium carbonate, 13 parts (solid) of styrene-butadiene latex, and 5 parts (solid) of 35% starch solution was prepared. The resulting coating color was coated on a 127 g/m2 fine coating base paper to a dry coating weight of 14 g/m2 by a blade coater at a coating speed of 500 m/min, and dried to obtain a base material (pigment coated paper) having a pigment coating layer and a moisture content of 5.5~.
Example 1 A 30~ solid surface color was prepared by diluting i,A2153182 100 parts (solid) of the copolymer latex (A) having a secondary transition temperature of 170oC and an average particle diameter of 75 nm with water. The resulting coating color was coated on the above base paper (pigment coated paper) to a dry coating weight of 1.6 g/m2 per one side by a blade coater at a coating speed of 500 m/min, and dried to obtain a coated printing paper having a moisture content of 6.5~s.
Comparative Exam les 1 and 2 In Comparative Example 1, the pigment coated paper as a base paper used in Example 1 was used, as is, as a coated printing paper. In Comparative Example 2, using a supercalender comprising a chilled roll and a cotton roll, the pigment coated surface of the pigment coated paper of Example 1 was contacted against the metal roll and 2-nip passed at a nip pressure of 180 kg/cm to obtain a coated printing paper.
Examples 2 and 3 In Example 2, a coated printing paper was prepared using the same procedure as Example 1, except that the composition of the surface layer coating color used in Example 1 was changed to a 30~ composition comprising 70 parts (solid) of the copolymer latex (A) having a secondary transition temperature of 170oC and an average particle diameter of 75 nm, and 30 parts (solid) of a plastic pigment (ROHPAQUE OP84 of Rohm & Haas Co.).
In Example 3, the same procedure as Example 1 was used, except that the composition of the surface layer coating color used in Example 1 was changed to 30 parts of the copolymer latex (A) and 70 parts (solid) of the plastic pigment (ROHPAQUE OP84 of Rohm & Haas Co.).
Examples 4 and 5 A 30~ solid surface layer costing color was prepared by mixing 65 parts (solid) of the copolymer latex (A) having a secondary transition temperature of 170oC and an average particle diameter of 75 nm, 25 parts (solid) of the plastic pigment (ROHPAQUE OP84 of Rohm & Haas Co.), and a lubricant comprising 5 parts (solid) of a polyethylene wax emulsion and 5 parts (solid) of calcium stearate. The resulting coating color was coated on the above base paper (pigment coated paper) to a dry coating weight of 1.6 g/m2 per one side by a blade coater at a coating speed of 500 m/min, and dried to obtain a coated paper having a surface layer with a moisture content of 6.5~. Using a supercalender comprising a chilled roll and a cotton roll, the coated surface was contacted against the metal roll and 2-nip passed at a nip pressure of 180 kg/cm and at a chilled roll temperature of 82oC to obtain a coated printing paper of Example 4.
In Example 5, a coated printing paper was prepared using the same procedure as example 4, except that the composition of the surface layer coating color of Example 4 was changed to 25 parts (solid) of the copolymer latex (A) and 65 parts (solid) of the plastic pigment (ROHPAQUE OP84 of Rohm & Haas Co.).
Examples 6,7 and 8, Com arative Exam le 3 A 30% solid surface layer coating color was prepared by mixing 90 parts (solid) of the copolymer latex (A) having a y 71142-44 ''~ CA2153182 secondary transition temperature of 107oC and an average particle diameter of 75 nm, and a lubricant comprising 5 parts (solid) of a polyethylene wax emulsion and 5 parts (solid) of calcium stearate. The resulting coating color was coated on the above base paper (pigment coated paper) to a dry coating weight of 1.6 g/m2 per one side by a blade coater at a coating speed of 500 m/min, and dried to obtain a coated paper having a surface layer with a moisture content of 6.5~. Using a supercalender comprising a chilled roll and a cotton roll, the coated surface of the coated paper was contacted against the metal roll and 2-nip passed at a nip pressure of 180 kg/cm and at a chilled roll temperature of 65°C to obtain a coated printing paper of Example 6. Further, a chilled roll temperature of 82°C was used to obtain a coated printing piper of Example 7.
Separately, using a gloss calender comprising a chilled roll and a heat-resistant rubber roll, the coated surface of the surface coated paper was contacted against the metal roll and 2-nip passed at a nip pressure of 100 kg/cm to obtain a high gloss coated printing paper. The chilled roll temperature was adjusted to 95oC to obtain a coated printing paper of Example 9, and the chilled roll temperature was adjusted to 120°C, which is higher than the secondary transition temperature of the copolymer latex, to obtain a coated printing paper of Comparative Example 3.
Examples 9, 10 and 11 The surface layer coating weight in Example 7 was s 71142-44 readjusted to 0.7 g/m2, 2.8 g/m2, and 5.5 g/m2 to obtain Examples 9, 10 and 11, respectively.
Examples 12 and 13. Comparative Example 4 A 20% solid surface layer coating color was prepared by mixing 80 parts (solid) of the copolymer latex (B) having a secondary transition temperature of 85°C and an average particle diameter of 67 nm, and a lubricant comprising 10 parts (solid) of a polyethylene wax emulsion and 10 parts (solid) of calcium stearate. The resulting coating color was coated on the above base paper (pigment coated paper) to a dry coating weight of 1.2 g/m2 per one side by a blade coater at a coating speed of 500 m/min, and dried to obtain a coated paper having a surface layer with a moisture content of 6.5%. Using a supercalender comprising a chilled roll and a cotton roll, the coated surface was contacted against the metal roll and 2-nip passed at a nip pressure of 180 kg/cm to obtain a coated printing paper. Further, a chilled roll temperature of 65°C
was used to obtain a coated printing paper of Example 12, and a temperature of 82°C was used to obtain a coated printing paper of Example 13.
Separately, using a gloss calender comprising a chilled roll and a heat-resistant rubber roll, the coated surface was contacted against the metal roll, the chilled roll temperature was adjusted to 120°C, which was higher than the secondary transition temperature of the copolymer latex, and 2-nip passed at a nip pressure of 100 kg/cm to obtain Comparative Example 4.
r 71142-44 Comparative Examples 5 and 6 A coated printing paper was obtained using the same procedure as Example 6, except that a copolymer latex (C) having a secondary transition temperature of 68°C and an average particle diameter of 70 nm was used as a surface layer coating copolymer latex, and the dry coating weight of the surface coating layer was adjusted to 1.4 g/m2. The chilled roll temperature was adjusted to 65°C, which was lower than the secondary transition temperature, to obtain Comparative Example 5, and the temperature was adjusted to 95°C, higher than the secondary transition temperature, to obtain Comparative Example 6.
Comparative Example 7 A coated printing paper was obtained using the same procedure as Example 13, except that the copolymer latex (B) was used directl on a 127 2 y g/m fine paper having no pigment coating layer and the surface layer coating color was coated to a dry coating weight of 2.6 g/m2.
Copolymer latices and metal roll surface temperatures during calendering used in the Examples and Comparative Examples are shown in Tables 1 and 2. Further, quality evaluation test results of the thus obtained coated paper are shown in Tables 3 and 4. Evaluation items and test methods described in Tables 3 and 4 are as follows.
White paper gloss: Measured by 60° reflection method using a Murakami type gloss meter. Since a high gloss was difficult to be exactly evaluated by 75° reflection, which is normally used for the gloss test, 60° reflection was used.
~~ CA~~~~~~.~
As standards of white paper gloss, reflectivities at 60° and 75° of general coated paper (CT: NPi Coat*, Nippon Paper Co.), superart paper (SA: SA KANEFUJI*, Kanzaki Seishi), and *
cast coat paper (CC: MIRROR COAT PLANTINA , Kanzaki Seishi) are shown. The present invention has a gloss higher than that of general coated paper.
( 60° ref lest ion ) ( 7 5° ref lect ion ) CT: 22.0% 63.5%
SA: 54.1% 83.6%
CCs 63.6% 84.7%
Print gloss: Printing was made by an RI-II type print tester, and a gloss was measured by 75° reflection by means of a Murakami type gloss meter.
Ink Set: Printing was made by an RI-II type print tester, and a white paper was pressed against the printed surface to visually ink transfer to the white paper.
Evaluation criteria: A indictes no ink transfer to the white paper, 8 indicates partial ink transfer, and C indicates considerable ink transfer.
Dry pick: This is a test to indicate the pick strength of the surface of coated printing paper. Printing was made by an RI-II print tester using ink tack No.20 ink having a high tack, and degree of picking was visually evaluated. Evaluation criteria: A indicates no picking, H
indicates partial picking, and C indicates considerable picking.
r 71142-44 ~A~ ~ ~~ ~ ~z Gravure printing adaptability= Using a grawre prlnt tester (Kumagaya Riki), printing was made using a dot grawre plate, and the rate (%) of generated mis-dot to the total dot number was determined.
' 71142-44 v o _ _ _ _ _ _ _ _ N N N In N Lf1 N _ OD CO OD l0 00 01 OD N
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CA~i~3 As can be seen from Tables 1 to 4, the coated printing paper of the present invention exhibits a gloss comparable to that of coated paper even without calendering, and is also much superior in printing adaptability such as ink set and dry pick. By calendering, a high gloss paper with a gloss higher than superart paper can be obtained. Printing adaptability such as ink set, dry pick , and mis-dot rate is much superior or in practically usable level. Adherence of the polymer latex to the calender roll during calendering, which is a measure of difficulty of production, is good or practically usable.
On the other hand, comparative examples are all insufficient in gloss, and further inferior in one of measures indicating the printing adaptability, or insufficient in peeling from the calender roll during calendering, and do not attain the object of the present invention.
According to the present invention, a pigment coating layer is provided on the base material, a polymer latex having a secondary transition temperature of higher than 80°C is coated on the pigment coating layer, and dried to obtain a gloss comparable to that of coated paper. Further, according to the present invention, a coated paper, which is superior in printing adaptability such as ink absorptivity and surface strength, can be produced. Still further, by calendering the surface layer at a temperature lower than the secondary transition temperature of the polymer latex, a high gloss paper comparable to or better than superart paper can be obtained, and at the same time, the printing adaptability such .4 as ink absorptivity, surface peeling strength, and missing-dot rate is practically sufficient, and adherence to the calender roll is eliminated, thereby the productivity is enhanced to achieve efficient production.
The inventors have previously proposed, in Japanese Patent Unexamined Publication No. 3-167396, a method in which a base material comprising a substrate coated thereon with a pigment coating layer is coated on the pigment coating layer with a surface layer comprising a thermoplastic polymer latex having a secondary transition temperature of higher than 80°C, and the surface layer is calendered at a temperature below the secondary transition temperature. After that, having conducted studies, the inventors have found that the above object is attained by using a thermoplastic polymer latex having a very small particle diameter, without necessarily requiring a calender treatment. Therefore, the present invention provides a coated printing paper having as pigment containing layer on at least one side of a substrate, characterized in that a surface layer containing thermoplastic polymer latex particles having an average particle diameter of less than 100 nm and having a secondary transition temperature of higher than 80°C is provided on the pigment containing layer, and the surface layer is not necessarily calendered.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an electron microscopic photograph of a surface layer of a coated printing paper according to a preferred embodiment of the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
In general, as the printing base material, paper, synthetic paper, plastic films, non-woven fabrics, and the like are used, and of these materials, paper is the most commonly used. The paper includes pigment coated papers such as art paper, coated paper, slightly coated paper, and coated white board, and uncoated papers such as fine paper, medium grade paper, newsprint paper, one side glazed paper, and special gravure paper.
In the present invention, the base material used for achieving both high gloss and printing adaptability must be, among the above printing base materials, one which is provided with a pigment containing layer on the substrate. The substrate may be one which can be provided thereon with the pigment containing layer, is not specifically limited, and an uncoated paper such as medium grade paper or fine paper is preferable. Formation of the pigment containing layer on the uncoated paper is sufficiently achieved by a production method of conventional pigment coated paper, in which types of the pigment and binder in the coating color and the ratio of the pigment and the binder are appropriately controlled according to the desired quality. The pigment coated paper is a one- or two-sided paper of a coating weight of the coating layer of 2 to 40 g/m2 per one side. After pigment coating, a thermoplastic polymer latex is coated on the pigment coating layer to form a surface layer. However, the pigment coating layer may be smoothened by a supercalender or a gloss calender before top coating. When the thermoplastic polymer latex containing layer is formed directly on the uncoated paper without providing a pigment containing layer, printing a adaptability is ensured, but a high gloss as expected cannot be obtained.
Further, when a synthetic paper or plastic film is used as a substrate, and the thermoplastic polymer latex layer is formed directly on the substrate without proving a pigment containing layer, a desirable gloss can be obtained, but dryability of ink is insufficient and no printing adaptability is obtained. The thermoplastic polymer latex used in the present invention is an emulsion of a polymer or copolymer having a thermoplasticity, having a secondary transition temperature of higher than 80°C and an average particle diameter of less than 100 nm (hereinafter an emulsion of a polymer or copolymer having a thermoplasticity is simply referred to "polymer latex"). For core-shell type latex, the secondary transition temperature of the shell portion must be higher than 80°C. Type and production method of the monomer constituting the polymer latex are not specifically limited if the secondary transition temperature is higher than 80oC.
Preferable monomers include styrene and its derivative, vinylidene chloride, acrylic or methacrylic esters.
Upper limit of the secondary transition temperature of the polymer latex is not specifically limited. It is mainly determined by the types of the monomer and the plasticizes in the production of the polymer latex, and is normally about 130°C.
When a polymer latex of a secondary transition temperature of below 80oC is used, the paper tends to adhere to the calender roll during calendering, the resulting coated paper is insufficient in gloss, weak in the pick strength of the surface layer, no printing adaptability is obtained, and the object of the present invention is not attained.
In general, the particle diameter of latices used in paper coating application is smaller than that for other applications such as paint, and is mainly an average particle diameter of about 200 nm to 1,000 nm. However, the polymer latex of the present invention has an even smaller average particle diameter of less than 100 nm. Hy using a latex less than 100 nm in average particle diameter, a high gloss can be obtained without special smoothing treatment, which is comparable to that of general coated paper smoothened by a gloss calender or supercalender. However, if the coating layer of the polymer latex of the present invention is smoothened, a printing paper of very high gloss can be obtained. The smoothing treatment can be achieved by a supercalender or gloss calender used for treatment of general coated paper, which may be used in combination. However, the calendering condition is important, which must be at a temperature lower than the secondary transition temperature of the polymer latex used in the surface layer. The calendering temperature is not specifically limited if it is below the secondary transition temperature, and the temperature of more than 5oC lower, preferably 10 to 30oC lower than the secondary transition temperature of the polymer latex. If the treatment temperature is higher than the secondary transition temperature of the polymer latex used, the latex melts to form a film, the ink acceptability is extremely decreased, and the _ 7 _ ~, 71142-44 object of the present invention is not attained. Further, when the polymer latex begins to melt, the coating layer increases in stickiness, the coating layer tends to stick to the calender roll, and the smoothing treatment becomes impossible.
Therefore, it is desirable to add an appropriate amount of a lubricant to the polymer latex used according to the present invention. In general, a type of lubricant which is used as an external lubricant, among those used in plastic molding, is suitable for the present invention. As the external lubricants, those which are described in page 945 and after of "Handbook of Plastic and Rubber Additives, Revised and Enlarged Edition" (published by Kagakukogyosha, July 1989) are used. For the present invention, one or more lubricants selected from stearic acid and its derivatives, olelC acid and its derivatives, and polyethylene wax emulsion are preferably used alone or in combination. The content of the lubricants is determined from types of the lubricants and the polymer latex of the present invention, condition and degree of smoothing treatment, amounts and types of other additives, and the like. In the present invention, the lubricant is preferably used in an amount of about 5 to 40% by weight, more preferably 10 to 25% by weight, of the surface layer coating color containing the polymer latex particles of the present invention.
The polymer latex of the present invention is normally coated alone on the pigment coating layer. However, in additlon to the lubricants, plastic pigments, natural or _ g _ A
synthetic resin binders, flow modifiers and deformers, coloring agents, inorganic white pigments, and like may be appropriately added as far as the object of the present invention is not impaired, to obtain the surface layer coating color.
The plastic pigment used in the present invention is synthetic polymer particles mainly comprising polystyrene having an average particle diameter of more than 100 nm, including a type which has no substantial binding power in itself, and a type which has some binding power. An example of the former is hollow plastic pigment Rohpaque OP84 of Rohm & Haas Co., and an example of the latter in Nipol LX407HP of Nippon Zeon. When these plastic pigments are used in combination with the polymer latex of the present invention, it is appropriate to add the plastic pigment in an amount of less than 60~ by weight, preferably 20 to 40~ by weight, to the polymer latex of the present invention. Using the plastic pigment, the gloss and surface strength can be controlled.
The present invention basically does not use a so called binder. However, a small amount of a natural or synthetic resin binder for general-purpose coating may be used in order to adjust the surface strength of the coating layer, but the amount should be to an extent that the surface does not have a stickiness. Types of additives such as follow modifiers, defoamers, coloring agents, and inorganic white pigments of the coating color are those used in general paper, and the amounts thereof should be to an extent that generation of gloss and surface strength is not impaired.
_ g _ * Trade Mark 71142-44 y LA~1531 E2 The thus obtained surface layer coating color is coated on the pigment coating layer to form the surface layer.
The coating amount can be appropriately controlled so that the desired properties are obtained but, if the coating amount is excessive, not only the cost is increased, but also the ink absorptivity decreases. This results in insufficient ink set, and the surface strength is decreased. Therefore, an excessively large coating amount is not desirable, and normally a coating weight of more than 0.1 g/m2 per one side, preferably 0.3 to 3 g/m2 is sufficient.
Coating of the surface layer coating color is achieved by a blade coater, a roll coater, an air knife coater, a bar coater, a gravure coater, a flexographic coater, and the like which are normally used in the field of paper coating. Drying after coating does nat require a special condition when the polymer latex of the present invention is used, and an optimum surface layer can be obtained by a drying condition used in the production of ordinary coated paper.
For example, even in drying by hot air at 150°C, the temperature of the surface layer is as high as 80°C, and when the secondary transition temperature of the polymer latex of the present invention is higher than 80oC, the latex will never melt to form a film.
The reason why the coated printing paper of the present invention is practically sufficient in printing adaptability and has a high gloss has yet to be elucidated, but is presumed from observation by an electron microscope of the surface gloss layer of the coated paper obtained by the present invention as follows.
As can be seen from Fig. 1 the surface layer is not a continuous uniform film of molten polymer latex, but polymer latex particles of several tens of nm are closely arranged.
This is because the polymer latex used according to the present invention has a high secondary transition temperature of higher than 80°C, which does not melt under normal drying condition and maintains the shape of the polymer particles and, after calendering as necessary, the latex particles do not melt to form a continuous film, but fixes remaining the particle shape, as far as the temperature of the surface layer is lower than the secondary transition temperature of the polymer latex. As a result, there are a number of voids between particles of the polymer latex, thereby the printing ink is maintained between the voids, passes through capillaries between particles, penetrates to the pigment coating layer to be absorbed.
According to a known theory, the latex unmelted and maintaining the particle shape as shown in Fig. 1 should have no strength as a film, but the surface gloss layer of the present invention has a practically sufficient surface strength. The reason therefor is unknown at present, but it is considered that the polymer latex of the present invention having a secondary transition temperature of higher than 80oC
has some hardness during calendering, when such a latex is coated on the pigment coating layer and calendered, probably due to physical properties of the polymer latex determined by properties such as density and elasticity of the pigment "''~' coating layer, and chemical affinity between latices.
Further, from the common sense that a possibly uniform continuous surface is required to obtain a high gloss, it is cont racy to the expectation and is surprising that a high gloss is obtained despite that the coating layer surface of the polymer latex of the present invention maintains the particle shape. Possibly, this is presumed as due to the fact that the particle diameter of the polymer latex is small, the polymer latex mainly fills recesses of the pigment coating layer, and the surface layer is optically smoothened as a whole.
However, from the fact that the surface layer condition of the coated printing paper, which will be described later, maintains the particle shape of the polymer latex as in Fig. 1, it is strongly hypothesized that another factor is related to the function of providing the effect of the present invention, but which has yet to be elucidated.
Further, in the production of the coated printing paper, since the drying condition and calendering condition are unchanged from those of ordinary coated paper, a constant quality can be obtained without impairing the productivity.
DETAILED DESCRIPTION OF PREFERRED EXAMPLES
The present invention will be described in detail with reference to the Examples. However, the present invention is not limited to the Examples. Part and % used in the Examples, unless otherwise noted, indicate part by weight and % by weight, respectively.
CA21~3182 Production of the polymer latex Production Example 1 In a four-necked flask having a stirrer, a thermometer, a condenser, a dropping funnel, and a nitrogen gas introduction tube, 300 parts of water, 9 parts of sodium dodecylbenzenesulfonate, and 4 parts of polyoxyethylene-phenolether (10 mole of ethyleneoxide added) were placed, mixed with 60 parts of a monomer mixture of 80 parts of styrene, 10 parts of a-methylstyrene, 100 parts of methyl methacrylate, and 10 parts methacrylic acid, the temperature was increased to 60oC under nitrogen purging, mixed with 7.2 parts of 20% aqueous ammonium persulfate solution and 4.8 parts of 20% aqueous sodium bisulfite solution, and polymerized for 60 minutes. After 10 parts of 20% aqueous ammonium persulfate solution was added, the remnant 140 parts of the monomer mixture was added dropwise over a period of 1 hour. The reaction mixture was maintained at 90°C for 4 hours to complete polymerization to obtain an ethylenic monomer copolymer latex (A) having a secondary transition temperature of 107°C, an average particle diameter of 75 nm, and a solid content of 39%.
Production Exam le 2 In a four-necked flask having a stirrer, a thermometer, a condenser and a nitrogen gas introduction tube, 310 parts of water, 5.6 parts of HITENOL N-68 (polyoxyethylene nonylphenylether sulfate ester salt, Daiichi Kogyo Seiyaku), 48 parts of styrene, 19 parts of methyl methacrylate, 8 parts of ethyl methacrylate, 2.5 parts of * Trade Mark 71142-44 divinylbenzene, and 2.5 parts of methacrylic acid were placed.
The temperature was increased to 70oC under nitrogen purging, mixed with 5 parts of 16~ aqueous ammonium persulfate solution, maintained at 85oC for 4 hours to complete polymerization to obtain an ethylenic monomer copolymer latex (H) having a secondary transition temperature of 85oC, an average particle diameter of 75 nm, and a solid content of 21.2%.
Production Example 3 The same procedure as Production Example 1 was used, except that the monomers were replaced with 88 parts of styrene, 38 parts of methyl methacrylate, 70 parts of n-butyl methacrylate, and 4 parts of methacrylic acid, to obtain a copolymer latex (C) having a secondary transition temperature of 68°C, an average particle diameter of 70 nm, and a solid content of 39~.
Production of base material ( iament coated paper) A 64% solid coating color for coated paper comprising 70 parts of US NO.1 kaolin, 30 parts of fine particle ground calcium carbonate, 13 parts (solid) of styrene-butadiene latex, and 5 parts (solid) of 35% starch solution was prepared. The resulting coating color was coated on a 127 g/m2 fine coating base paper to a dry coating weight of 14 g/m2 by a blade coater at a coating speed of 500 m/min, and dried to obtain a base material (pigment coated paper) having a pigment coating layer and a moisture content of 5.5~.
Example 1 A 30~ solid surface color was prepared by diluting i,A2153182 100 parts (solid) of the copolymer latex (A) having a secondary transition temperature of 170oC and an average particle diameter of 75 nm with water. The resulting coating color was coated on the above base paper (pigment coated paper) to a dry coating weight of 1.6 g/m2 per one side by a blade coater at a coating speed of 500 m/min, and dried to obtain a coated printing paper having a moisture content of 6.5~s.
Comparative Exam les 1 and 2 In Comparative Example 1, the pigment coated paper as a base paper used in Example 1 was used, as is, as a coated printing paper. In Comparative Example 2, using a supercalender comprising a chilled roll and a cotton roll, the pigment coated surface of the pigment coated paper of Example 1 was contacted against the metal roll and 2-nip passed at a nip pressure of 180 kg/cm to obtain a coated printing paper.
Examples 2 and 3 In Example 2, a coated printing paper was prepared using the same procedure as Example 1, except that the composition of the surface layer coating color used in Example 1 was changed to a 30~ composition comprising 70 parts (solid) of the copolymer latex (A) having a secondary transition temperature of 170oC and an average particle diameter of 75 nm, and 30 parts (solid) of a plastic pigment (ROHPAQUE OP84 of Rohm & Haas Co.).
In Example 3, the same procedure as Example 1 was used, except that the composition of the surface layer coating color used in Example 1 was changed to 30 parts of the copolymer latex (A) and 70 parts (solid) of the plastic pigment (ROHPAQUE OP84 of Rohm & Haas Co.).
Examples 4 and 5 A 30~ solid surface layer costing color was prepared by mixing 65 parts (solid) of the copolymer latex (A) having a secondary transition temperature of 170oC and an average particle diameter of 75 nm, 25 parts (solid) of the plastic pigment (ROHPAQUE OP84 of Rohm & Haas Co.), and a lubricant comprising 5 parts (solid) of a polyethylene wax emulsion and 5 parts (solid) of calcium stearate. The resulting coating color was coated on the above base paper (pigment coated paper) to a dry coating weight of 1.6 g/m2 per one side by a blade coater at a coating speed of 500 m/min, and dried to obtain a coated paper having a surface layer with a moisture content of 6.5~. Using a supercalender comprising a chilled roll and a cotton roll, the coated surface was contacted against the metal roll and 2-nip passed at a nip pressure of 180 kg/cm and at a chilled roll temperature of 82oC to obtain a coated printing paper of Example 4.
In Example 5, a coated printing paper was prepared using the same procedure as example 4, except that the composition of the surface layer coating color of Example 4 was changed to 25 parts (solid) of the copolymer latex (A) and 65 parts (solid) of the plastic pigment (ROHPAQUE OP84 of Rohm & Haas Co.).
Examples 6,7 and 8, Com arative Exam le 3 A 30% solid surface layer coating color was prepared by mixing 90 parts (solid) of the copolymer latex (A) having a y 71142-44 ''~ CA2153182 secondary transition temperature of 107oC and an average particle diameter of 75 nm, and a lubricant comprising 5 parts (solid) of a polyethylene wax emulsion and 5 parts (solid) of calcium stearate. The resulting coating color was coated on the above base paper (pigment coated paper) to a dry coating weight of 1.6 g/m2 per one side by a blade coater at a coating speed of 500 m/min, and dried to obtain a coated paper having a surface layer with a moisture content of 6.5~. Using a supercalender comprising a chilled roll and a cotton roll, the coated surface of the coated paper was contacted against the metal roll and 2-nip passed at a nip pressure of 180 kg/cm and at a chilled roll temperature of 65°C to obtain a coated printing paper of Example 6. Further, a chilled roll temperature of 82°C was used to obtain a coated printing piper of Example 7.
Separately, using a gloss calender comprising a chilled roll and a heat-resistant rubber roll, the coated surface of the surface coated paper was contacted against the metal roll and 2-nip passed at a nip pressure of 100 kg/cm to obtain a high gloss coated printing paper. The chilled roll temperature was adjusted to 95oC to obtain a coated printing paper of Example 9, and the chilled roll temperature was adjusted to 120°C, which is higher than the secondary transition temperature of the copolymer latex, to obtain a coated printing paper of Comparative Example 3.
Examples 9, 10 and 11 The surface layer coating weight in Example 7 was s 71142-44 readjusted to 0.7 g/m2, 2.8 g/m2, and 5.5 g/m2 to obtain Examples 9, 10 and 11, respectively.
Examples 12 and 13. Comparative Example 4 A 20% solid surface layer coating color was prepared by mixing 80 parts (solid) of the copolymer latex (B) having a secondary transition temperature of 85°C and an average particle diameter of 67 nm, and a lubricant comprising 10 parts (solid) of a polyethylene wax emulsion and 10 parts (solid) of calcium stearate. The resulting coating color was coated on the above base paper (pigment coated paper) to a dry coating weight of 1.2 g/m2 per one side by a blade coater at a coating speed of 500 m/min, and dried to obtain a coated paper having a surface layer with a moisture content of 6.5%. Using a supercalender comprising a chilled roll and a cotton roll, the coated surface was contacted against the metal roll and 2-nip passed at a nip pressure of 180 kg/cm to obtain a coated printing paper. Further, a chilled roll temperature of 65°C
was used to obtain a coated printing paper of Example 12, and a temperature of 82°C was used to obtain a coated printing paper of Example 13.
Separately, using a gloss calender comprising a chilled roll and a heat-resistant rubber roll, the coated surface was contacted against the metal roll, the chilled roll temperature was adjusted to 120°C, which was higher than the secondary transition temperature of the copolymer latex, and 2-nip passed at a nip pressure of 100 kg/cm to obtain Comparative Example 4.
r 71142-44 Comparative Examples 5 and 6 A coated printing paper was obtained using the same procedure as Example 6, except that a copolymer latex (C) having a secondary transition temperature of 68°C and an average particle diameter of 70 nm was used as a surface layer coating copolymer latex, and the dry coating weight of the surface coating layer was adjusted to 1.4 g/m2. The chilled roll temperature was adjusted to 65°C, which was lower than the secondary transition temperature, to obtain Comparative Example 5, and the temperature was adjusted to 95°C, higher than the secondary transition temperature, to obtain Comparative Example 6.
Comparative Example 7 A coated printing paper was obtained using the same procedure as Example 13, except that the copolymer latex (B) was used directl on a 127 2 y g/m fine paper having no pigment coating layer and the surface layer coating color was coated to a dry coating weight of 2.6 g/m2.
Copolymer latices and metal roll surface temperatures during calendering used in the Examples and Comparative Examples are shown in Tables 1 and 2. Further, quality evaluation test results of the thus obtained coated paper are shown in Tables 3 and 4. Evaluation items and test methods described in Tables 3 and 4 are as follows.
White paper gloss: Measured by 60° reflection method using a Murakami type gloss meter. Since a high gloss was difficult to be exactly evaluated by 75° reflection, which is normally used for the gloss test, 60° reflection was used.
~~ CA~~~~~~.~
As standards of white paper gloss, reflectivities at 60° and 75° of general coated paper (CT: NPi Coat*, Nippon Paper Co.), superart paper (SA: SA KANEFUJI*, Kanzaki Seishi), and *
cast coat paper (CC: MIRROR COAT PLANTINA , Kanzaki Seishi) are shown. The present invention has a gloss higher than that of general coated paper.
( 60° ref lest ion ) ( 7 5° ref lect ion ) CT: 22.0% 63.5%
SA: 54.1% 83.6%
CCs 63.6% 84.7%
Print gloss: Printing was made by an RI-II type print tester, and a gloss was measured by 75° reflection by means of a Murakami type gloss meter.
Ink Set: Printing was made by an RI-II type print tester, and a white paper was pressed against the printed surface to visually ink transfer to the white paper.
Evaluation criteria: A indictes no ink transfer to the white paper, 8 indicates partial ink transfer, and C indicates considerable ink transfer.
Dry pick: This is a test to indicate the pick strength of the surface of coated printing paper. Printing was made by an RI-II print tester using ink tack No.20 ink having a high tack, and degree of picking was visually evaluated. Evaluation criteria: A indicates no picking, H
indicates partial picking, and C indicates considerable picking.
r 71142-44 ~A~ ~ ~~ ~ ~z Gravure printing adaptability= Using a grawre prlnt tester (Kumagaya Riki), printing was made using a dot grawre plate, and the rate (%) of generated mis-dot to the total dot number was determined.
' 71142-44 v o _ _ _ _ _ _ _ _ N N N In N Lf1 N _ OD CO OD l0 00 01 OD N
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CA~i~3 As can be seen from Tables 1 to 4, the coated printing paper of the present invention exhibits a gloss comparable to that of coated paper even without calendering, and is also much superior in printing adaptability such as ink set and dry pick. By calendering, a high gloss paper with a gloss higher than superart paper can be obtained. Printing adaptability such as ink set, dry pick , and mis-dot rate is much superior or in practically usable level. Adherence of the polymer latex to the calender roll during calendering, which is a measure of difficulty of production, is good or practically usable.
On the other hand, comparative examples are all insufficient in gloss, and further inferior in one of measures indicating the printing adaptability, or insufficient in peeling from the calender roll during calendering, and do not attain the object of the present invention.
According to the present invention, a pigment coating layer is provided on the base material, a polymer latex having a secondary transition temperature of higher than 80°C is coated on the pigment coating layer, and dried to obtain a gloss comparable to that of coated paper. Further, according to the present invention, a coated paper, which is superior in printing adaptability such as ink absorptivity and surface strength, can be produced. Still further, by calendering the surface layer at a temperature lower than the secondary transition temperature of the polymer latex, a high gloss paper comparable to or better than superart paper can be obtained, and at the same time, the printing adaptability such .4 as ink absorptivity, surface peeling strength, and missing-dot rate is practically sufficient, and adherence to the calender roll is eliminated, thereby the productivity is enhanced to achieve efficient production.
Claims (15)
1. A coated printing paper comprising a substrate having a pigment-containing layer at least on one side, characterized in that a surface layer containing thermoplastic polymer latex particles having an average particle diameter of less than 100 nm and a secondary transition temperature of higher than 80°C is provided on the pigment containing layer, and said surface layer is not necessarily calendered.
2. The coated printing paper of Claim 1, wherein the surface layer contains a mixture of the thermoplastic polymer latex particles and a plastic pigment having an average particle diameter of greater than 100 nm, and a content of the thermoplastic polymer latex particles is more than 40% by weight of the mixture.
3. The coated printing paper of Claim 1, wherein a coating weight of the surface layer is 0.3 to 4 g/m2.
4. The coated printing paper of Claim 1, 2 or 3, wherein the surface layer contains a lubricant in an amount of to 40% by weight of the surface layer.
5. A coated printing paper comprising a substrate having a pigment-containing layer at least on one side, characterized in that a surface layer containing thermoplastic polymer latex particles having an average particle diameter of less than 100 nm and a secondary transition temperature of higher than 80°C is provided on the pigment containing layer, and the surface layer is calendered at a temperature lower than the secondary transition temperature of the polymer latex particles.
6. The coated printing paper of Claim 5, wherein the surface layer contains a lubricant in an amount of 5 to 40% by weight of the surface layer.
7. A method of producing a coated printing paper, which comprises:
(A) providing a printing base material comprising a substrate and a layer containing a pigment and a binder on at least one side of the substrate, (B) coating, on the pigment-containing layer of the printing base material, an emulsion of a thermoplastic polymer or copolymer which has a secondary transition temperature of higher than 80°C but not higher than 130°C and an average particle diameter of less than 100 nm, to form a surface layer, (C) drying the surface layer under such conditions that particles of the thermoplastic polymer or copolymer do not melt but maintain their shape, and (D) where required, calendering the surface layer at a temperature lower than the secondary transition temperature of the thermoplastic polymer or copolymer so that particles of the thermoplastic polymer or copolymer do not melt but maintain their shape.
(A) providing a printing base material comprising a substrate and a layer containing a pigment and a binder on at least one side of the substrate, (B) coating, on the pigment-containing layer of the printing base material, an emulsion of a thermoplastic polymer or copolymer which has a secondary transition temperature of higher than 80°C but not higher than 130°C and an average particle diameter of less than 100 nm, to form a surface layer, (C) drying the surface layer under such conditions that particles of the thermoplastic polymer or copolymer do not melt but maintain their shape, and (D) where required, calendering the surface layer at a temperature lower than the secondary transition temperature of the thermoplastic polymer or copolymer so that particles of the thermoplastic polymer or copolymer do not melt but maintain their shape.
8. The method of Claim 7, wherein the calendering step (D) is not carried out.
9. The method of Claim 7, wherein the calendering step (D) is carried out,
10. The method of Claim 9, wherein the emulsion of the thermoplastic polymer or copolymer also contains a lubricant in such an amount that the content of the lubricant is 5 to 40% by weight of the surface layer.
11. The method of Claim 10, wherein the lubricant comprises at least one member selected from the group consisting of stearic acid, calcium stearate, oleic acid and polyethylene wax emulsion.
12. The method of any one Claims 7 through 11, wherein the particles of the thermoplastic polymer or copolymer have an average particle size of from 67 nm to less than 100 nm.
13. The method of any one of Claims 7 through 11, wherein the emulsion of the thermoplastic polymer or copolymer further contains a plastic pigment having an average particle diameter of greater than 100 nm in such an amount that the content of the thermoplastic polymer or copolymer is more than 40% by weight based on the total amount of the plastic pigment and the thermoplastic polymer or copolymer.
14. The method of any one of Claims 7 through 11, wherein the emulsion is of a copolymer of monomers selected from the group consisting of styrene, .alpha.-methylstyrene, methyl methacrylate, methacrylic acid, ethyl methacrylate, n-butyl methacrylate and divinylbenzene.
15. The method of Claim 14, wherein the copolymer is a member selected from the group consisting of:
(a) a copolymer of styrene, .alpha.-methylstyrene, methyl methacrylate and methacrylic acid, (b) a copolymer of styrene, methyl methacrylate, ethyl methacrylate, divinyl benzene and methacrylic acid, and (c) a copolymer of styrene, methyl methacrylate, n-butyl methacrylate and methacrylic acid.
(a) a copolymer of styrene, .alpha.-methylstyrene, methyl methacrylate and methacrylic acid, (b) a copolymer of styrene, methyl methacrylate, ethyl methacrylate, divinyl benzene and methacrylic acid, and (c) a copolymer of styrene, methyl methacrylate, n-butyl methacrylate and methacrylic acid.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6186908A JP2940851B2 (en) | 1994-07-05 | 1994-07-05 | Coated paper for printing |
| JP186908/94 | 1994-07-05 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2153182A1 CA2153182A1 (en) | 1996-01-06 |
| CA2153182C true CA2153182C (en) | 2000-09-12 |
Family
ID=16196795
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2153182 Expired - Fee Related CA2153182C (en) | 1994-07-05 | 1995-07-04 | Coated printing paper |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JP2940851B2 (en) |
| CA (1) | CA2153182C (en) |
| DE (1) | DE19524528C2 (en) |
| FI (1) | FI119946B (en) |
| SE (1) | SE513301C2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007118085A1 (en) * | 2006-04-07 | 2007-10-18 | Hewlett-Packard Development Company, L.P. | Media sheet |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1999063157A1 (en) * | 1998-06-02 | 1999-12-09 | The Mead Corporation | Printing paper |
| JP4048623B2 (en) * | 1998-12-10 | 2008-02-20 | 王子製紙株式会社 | Method for producing coated lightweight printing paper and coated lightweight printing paper |
| JP3867606B2 (en) * | 2001-03-29 | 2007-01-10 | 日本製紙株式会社 | Coated paper for printing |
| US6777075B2 (en) | 2002-03-15 | 2004-08-17 | S.D. Warren Services Company | Burnish resistant printing sheets |
| CN100360741C (en) * | 2002-03-28 | 2008-01-09 | 日本制纸株式会社 | Coated sheet for rotary offset printing |
| JP2007247081A (en) * | 2006-03-14 | 2007-09-27 | Jsr Corp | Organic pigment dispersion for paper coating, coated paper and method for producing the same |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS54151606A (en) * | 1978-05-16 | 1979-11-29 | Nippon Zeon Co | Paper coating composition |
| JP2643351B2 (en) * | 1988-09-07 | 1997-08-20 | 日本合成ゴム株式会社 | Lightweight coated paper |
| JP2856285B2 (en) * | 1989-11-27 | 1999-02-10 | 日本製紙株式会社 | Printing coated paper and method for producing the same |
| JPH03279493A (en) * | 1990-03-26 | 1991-12-10 | Nippon Zeon Co Ltd | Pigment coating composition |
| JPH04272297A (en) * | 1991-02-27 | 1992-09-29 | Harima Chem Inc | Surface finishing agent of paper |
-
1994
- 1994-07-05 JP JP6186908A patent/JP2940851B2/en not_active Expired - Fee Related
-
1995
- 1995-07-04 FI FI953299A patent/FI119946B/en not_active IP Right Cessation
- 1995-07-04 SE SE9502422A patent/SE513301C2/en not_active IP Right Cessation
- 1995-07-04 CA CA 2153182 patent/CA2153182C/en not_active Expired - Fee Related
- 1995-07-05 DE DE1995124528 patent/DE19524528C2/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007118085A1 (en) * | 2006-04-07 | 2007-10-18 | Hewlett-Packard Development Company, L.P. | Media sheet |
| CN101416120B (en) * | 2006-04-07 | 2012-07-04 | 惠普发展公司，有限责任合伙企业 | Media sheet |
Also Published As
| Publication number | Publication date |
|---|---|
| SE9502422L (en) | 1996-01-06 |
| DE19524528A1 (en) | 1996-01-11 |
| CA2153182A1 (en) | 1996-01-06 |
| JPH0813390A (en) | 1996-01-16 |
| FI953299A (en) | 1996-01-06 |
| DE19524528C2 (en) | 2003-02-20 |
| SE513301C2 (en) | 2000-08-21 |
| FI119946B (en) | 2009-05-15 |
| SE9502422D0 (en) | 1995-07-04 |
| FI953299A0 (en) | 1995-07-04 |
| JP2940851B2 (en) | 1999-08-25 |
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