Source: http://www.google.fr/patents/US5635297?hl=fr
Timestamp: 2013-05-25 07:37:09
Document Index: 340612054

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Brevet US5635297 - Ink jet recording sheet - Google�BrevetsRecherche Images Maps Play YouTube Actualit�s Gmail Drive Plus » Recherche avanc�e dans les brevets | Historique Web | Connexion Recherche avanc�e dans les brevets BrevetsAn ink jet recording sheet which includes a support including a wood pulp and a pigment, an ink-receiving layer provided on one side of the support and a backcoat layer provided on the other side of the support, wherein the backcoat layer contains a binder containing a synthetic polymer having a glass...http://www.google.fr/patents/US5635297?utm_source=gb-gplus-shareBrevet US5635297 - Ink jet recording sheet Num�ro de publicationUS5635297 AType de publicationOctroi Num�ro de demande08/486,290 Date de publication3 juin 1997 Date de d�p�t7 juin 1995 Date de priorit�10 d�c. 1992Autre r�f�rence de publicationEP0602494A1EP0602494B1 InventeursKouji IdeiSusumu OgawaHideaki Senoh Cessionnaire d'origineMitsubishi Paper Mills Limited Classification aux �tats-Unis428/342428/535428/514428/537.5428/520347/105 Classification internationaleB41M5/50B41M5/00B41M5/52 Classification coop�rativeB41M5/504B41M5/508 Classification europ�enneB41M5/50B6B41M5/50B2R�f�rencesCitations de brevets (10)Citations hors brevets (2) R�f�renc� par (32)Liens externesUSPTO Cession USPTO EspacenetInk jet recording sheetUS 5635297 A R�sum� An ink jet recording sheet which includes a support including a wood pulp and a pigment, an ink-receiving layer provided on one side of the support and a backcoat layer provided on the other side of the support, wherein the backcoat layer contains a binder containing a synthetic polymer having a glass transition temperature of -50 least one water-soluble binder selected from a starch, a polyvinyl alcohol and a cellulose derivative. The ink jet recording sheet is less in undulation caused by absorption of ink after ink jet recording and has a curling resistance hardly susceptible to change in temperature and humidity.
What is claimed is: 1. An ink jet recording sheet which comprises a support comprising a wood pulp and a pigment, an ink-receiving layer provided on one side of the support and a backcoat layer provided on the other side of the support, wherein the backcoat layer contains a binder comprising a synthetic polymer having a glass transition temperature of -50 +25 group consisting of starches, polyvinyl alcohols and cellulose derivatives.
2. An ink jet recording sheet according to claim 1, wherein the glass transition temperature of the synthetic polymer is -40 +25
8. An ink jet recording sheet according to claim 1, wherein the coating amount W.sub.B of the backcoat layer is 3 g/m.sup.2 or more and the difference W.sub.B -W.sub.I from the coating amount W.sub.I of the ink-receiving layer is -10 to 25 g/m.sup.2.
BACKGROUND OF THE INVENTION The present invention relates to an ink jet recording sheet with which recording is performed using ink and in particular, to an ink jet recording sheet which is inhibited from occurrence of undulation of the sheet caused by absorption of ink after recording and which is assured in curling resistance hardly susceptible to change in temperature or humidity.
In order to avoid the occurrence of unevenness after printing, various proposals have been made and recently, it has been attempted to use a platy pigment and a binder having a glass transition temperature of 30 Patent Application Kokai No. 4-298380). It is generally said that a treatment at a temperature higher than the glass transition temperature is necessary for assuring adhesiveness using an emulsion type binder and a treatment at a temperature at least about 60 glass transition temperature is necessary for developing a complete adhesiveness (Soichi Muroi, "Polymer Latex Adhesives" published from Kobunshi Publishing Association). Thus, in order to maintain adhesiveness and inhibit peeling of the backcoat layer, it is essential to increase amount of the binder or to treat the backcoat layer at a temperature higher than the glass transition temperature, preferably at least about 60
SUMMARY OF THE INVENTION The object of the present invention is to provide an ink jet recording sheet which is inhibited from occurrence of undulation caused by absorption of ink after ink jet recording and surely possesses curling resistance unsusceptible to change in temperature and humidity.
According to the present invention, an ink jet recording sheet which is superior in adhesion strength and curling resistance and is inhibited from undulation after printing can be obtained by providing a backcoat layer containing a synthetic polymer latex having a glass transition temperature of -50 and the object of the present invention cannot be attained by use of the latex and the water-soluble binder each alone.
That is, the present invention provides an ink jet recording sheet comprising a support mainly composed of a wood pulp and a pigment and at least one ink-receiving layer coated on one side of the support and one backcoat layer coated on the other side of the support wherein a binder of the backcoat layer comprises a synthetic polymer latex having a glass transition temperature of -50 component and additionally at least one of starches, polyvinyl alcohols and cellulose derivatives which are water-soluble binders.
That is, the present invention further provides an ink jet recording sheet wherein the backcoat layer is mainly composed of a pigment and a binder and the pigment has an average equilibrium moisture content M of 1.9-5.5% by weight calculated from the following formula (1). ##EQU1## wherein M denotes an average equilibrium moisture content [% by weight], i denotes a variable which shows the kind of pigment, n denotes the number of the kind of the pigment contained (n≧1), Mi denotes an equilibrium moisture content of pigment i [% by weight], and Wi denotes a weight ratio of the pigment i to the total pigment (0&lt;Wi≦1).
Mi={(Si--Di)/Si}
wherein Si denotes a mass of the pigment i left to stand for 24 hours under the conditions of 20 pigment i left to stand for 3 hours under the condition of 105 The measurement of the equilibrium moisture content Mi is conducted in such a procedure that first Di of the pigment i is obtained and then, Si is obtained.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph which shows the relation between the average equilibrium moisture content of the pigment contained in the backcoat layer and the relative change in height of curl wherein curve 1 shows the relative change in height (H.sub.L) of curl at 5 curve 2 shows the relative change in height (H.sub.H) of curl at 40
FIG. 2 is a graph which shows the relation between the average equilibrium moisture content of the pigment contained in the backcoat layer and the difference in the relative change in height of curl wherein curve 3 shows the difference (H.sub.H -H.sub.L) between the curve H.sub.H and the curve H.sub.L.
DETAILED DESCRIPTION OF THE INVENTION The support which is used in the present invention and on which the ink-receiving layer and the backcoat layer are coated includes a base paper prepared by mixing a known pigment and a wood pulp, for example, a chemical pulp such as LBKP or NBKP, a mechanical pulp such as GP, PGW, RMP, TMP, CTMP, CMP or CGP or a recycled fiber such as DIP with a binder and optionally at least one of the additives such as sizing agent, fixing agent, retention aid, cationizing agent and paper strengthing agent and making the resulting mixture into a paper by various apparatuses such as Foudrinier paper machine, cylinder paper machine and twin wire paper machine. The support further includes the above base papers on which a size press coating layer or an anchor coat layer of starch, polyvinyl alcohol or the like and coated papers such as art papers, coated papers and cast coat papers. The ink-receiving layer may be provided on the resulting support as it is or the support may be subjected to calendering by machine calenders, TG calenders, soft calenders or the like for controlling the smoothness.
It is required that the synthetic polymer latexes have a glass transition temperature of -50 temperature can be obtained by changing the amount of the components or by blending two or more latexes. The glass transition temperature may also be adjusted by copolymerizing film forming aids or plasticizers such as higher alkyl acrylates and fumaric acid.
The polyvinyl alcohols used in the present invention are polymer compounds of the structural formula (CH.sub.2 C(OH)H).sub.n produced by hydrolysis of polyvinyl acetate and having the polymerization degree n of 500 or higher and a saponification degree of 87 or higher. If the polymerization degree is lower than 500 or the saponification degree is lower than 87, viscosity is low at the time of coating and control of coating amount is difficult. Preferably, the polymerization degree is 500-2500 and the saponification degree is 87 or higher though it depends on concentration of the coating composition. Use of a silanol group containing polyvinyl alcohol provides a backcoat layer high in water resistance against permeation of aqueous ink or moisture and the effect of the present invention can be further enhanced.
The object of the present invention is attained by containing a synthetic polymer latex having a glass transition temperature of -50 +25 one of starch, polyvinyl alcohol and water-soluble cellulose binders as binders for the pigment in the ink-receiving layer. If the coating amount of the backcoat layer is less than 3 g/m.sup.2, satisfactory curl resistance cannot be obtained and if it is more than 30 g/m.sup.2, rather undulation of the sheet occurs due to migration of the binder at the steps of coating and drying. Therefore, the coating amount is preferably 3-30 g/m.sup.2. The backcoat layer may further contain other additives such as pigment dispersant, thickening agent, fluidity improver, antifoamer, foam inhibitor, releasing agent, foaming agent, penetrant, coloring dye, coloring pigment, fluorescent brightener, ultraviolet absorber, antioxidant, preservative, slimecide, water proofing agent, wet strengthening agent and dry strengthening agent.
The coating weight W.sub.B of the backcoat layer is desirably set in connection with the coating weight W.sub.I of the ink-receiving layer. Preferably, W.sub.B is 3 g/m.sup.2 or more and (W.sub.B -W.sub.I) is -10 to 25 g/m.sup.2. If W.sub.B is less than 3 g/m.sup.2 or (W.sub.B -W.sub.I) is less than -10 g/m.sup.2, it is difficult to inhibit the curling of the sheet towards the ink-receiving layer side. Even if (W.sub.B -W.sub.I) is more than 25 g/m.sup.2, the effect to inhibit the curling cannot be enhanced and productivity decreases and this is not economical.
In order to prevent undulation of the sheet which occurs after printing and secure the curl resistance which are the objects of the present invention, it is necessary that the backcoat layer contains a synthetic polymer latex having a glass transition temperature of -50 preferably -40 additionally at least one of starches, polyvinyl alcohols and cellulose derivatives.
If the backcoat layer contains a synthetic polymer latex having a glass transition temperature of lower than -50 is inferior although adhesion strength is high and a problem is encountered that the recording sheets stick to each other. If the glass transition temperature of the latex is higher than +25 latex is not contained, adhesion strength decreases and in addition, occurrence of undulation of the sheet after printing cannot be inhibited by the backcoat layer. When amount of the latex is increased for avoiding decrease in pick resistance, the sheet has undulation already before printing.
Curling resistance cannot be secured unless starch, polyvinyl alcohol and/or cellulose derivative are used. This is considered to relate to the chain-like form of starch, polyvinyl alcohol and cellulose derivative and to the properties of the polymer shown by the glass transition temperature. That is, it is considered that when the backcoat layer containing the starch, polyvinyl alcohol and cellulose derivative having a chain-like form is coated and dried, the chain-like form is extended in the depth and planar directions of the backcoat layer to form a strong layer. Furthermore, it is considered that since the glass transition temperature of the starch, polyvinyl alcohol and cellulose derivative is generally higher than about +65 environmental temperature at which the ink jet recording apparatus is used, the backcoat layer containing the starch, polyvinyl alcohol and cellulose derivative inhibits the occurrence of curl in the ink jet recording sheet.
DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples are illustrative of the present invention and are not intended for purposes of limitation. All "part" and "%" are by weight unless otherwise notified.
Monochromatic dots of cyan ink, magenta ink and yellow ink are overlapped to print overlapped ink dots on the whole surface of the sheet (A4 size, 210 mm judged and graded by the following criteria. The grades A and B have no problem in quality.
Samples (A4 size) obtained in the following Examples and Comparative Examples are left to stand under each of the conditions: 5 C. C. heights (H) of curls at the four corners of the sample are measured. In this case, the sample is placed so that it curls upwardly and the height of the curl at the four corners is measured. The results are graded by the following criteria.
A: 0≦H&lt;5 (mm): Good
C: 10&lt;H (mm): Running property of sheet greatly deteriorates and this is practically unacceptable.
Ten sheets of the samples of A4 size were superposed and a weight of 3 kg was put thereon and these superposed sheets are left to stand for 24 hours under the conditions of 40 blocking is visually inspected and graded by the following criteria. The grades A and B mean that the samples have no problem in quality in this regards.
EXAMPLE 1 A support was produced by mixing 100 parts of a wood pulp comprising 80 parts of LBKP (freeness: 400 ml csf) and 20 parts of NBKP (freehess: 450 ml csf) with 25 parts of pigments comprising precipitated calcium carbonate/ground calcium carbonate/talc (30/35/35), 0.10 part of commercially available alkyl ketene dimer, 0.03 part of commercially available cationic acrylamide, 0.8 part of commercially available cationized starch and 0.4 part of aluminum sulfate and making the resulting mixture into a paper of 90 g/m.sup.2 in basis weight by a Fourdrinier paper machine. An ink-receiving layer and a backcoat layer were provided on the front side and on the back side of the resulting support, respectively and subjected to calendering treatment to obtain an ink jet recording sheet.
The ink-receiving layer was provided in the following manner. A coating composition for ink-receiving layer comprising 100 parts of a synthetic amorphous silica (Finesil X37B manufactured by Tokuyama Soda Co., Ltd.), 50 parts of polyvinyl alcohol (PVA 117 manufactured by Kuraray Co., Ltd.) and 20 parts of a cationic dye fixer (Sumirase Resin 1001 manufactured by Sumitomo Chemical Co., Ltd.) was prepared. The resulting coating composition had a solid concentration of 13%. The coating composition was coated on the front side of the support at a coating weight of 8 g/m.sup.2 by an airknife coater.
The backcoat layer was provided on another side of the support in the following manner. 100 parts of kaolin (Hydrasperse manufactured by Huber Corp.) was mixed with 5 parts of a silanol group containing polyvinyl alcohol (R Polymer 1130 manufactured by Kuraray Co., Ltd.) and 10 parts of an acrylic latex having a glass transition temperature of 25 (Boncoat AN 127 manufactured by Dainippon Ink & Chemicals Inc.) to prepare a coating composition of 35% in solid concentration for backcoat layer. The resulting coating composition was coated at a coating weight of 8 g/m.sup.2 on the opposite side to the ink-receiving layer side and subjected to calendering treatment to obtain an ink jet recording sheet.
EXAMPLES 2-15 AND COMPARATIVE EXAMPLES 1-6 The support and the ink-receiving layer were obtained in the same manner as in Example 1. The coating composition for the backcoat layer was prepared by mixing 100 parts of kaolin with the synthetic polymer latex as shown in Tables 1 and 2 and further with the polyvinyl alcohol, starch and cellulose derivative. The backcoat layer was provided in the same manner as in Example 1. In Comparative Example 6, the latex was not used.
TABLE 1__________________________________________________________________________               Example                    Example                          Example                               Example                                     Example                                          Example                                                Example                                                     Example               1    2     3    4     5    6     7    8__________________________________________________________________________[Support]LBKP (part)         80NBKP (part)         20Pigment (part)      25Precipitated calcium carbonate (part)               7.5Ground calcium carbonate (part)               8.75Talc (part)         8.75Alkyl ketene dimer (part)               0.10Cationic acrylamide (part)               0.03Cationized starch (part)               0.8Aluminum sulfate (part)               0.4Basis weight (g/m.sup.2)               90[Ink-receiving layer]Synthetic amorphous silica (part)               100PVA 117 (part)      50Cationic dye fixer (part)               20Solid concentration (%)               13Coating weight (g/m.sup.2)               8Coating method      Airknife[Backcoat layer]Kaolin (part)       100Equilibrium moisture content of pigment               1.2% by               weightSilanol group containing PVA (part)               5    --    --   5     5    5     5    --Polyvinyl alcohol.sup.1) (part)               --   --    --   --    --   --    --   --Oxidized starch (part)               --   5     --   --    --   --    --   --Phosphate esterified starch (part)               --   --    --   --    --   --    --   5Carboxymethylcellulose (part)               --   --    1    --    --   --    --   --Hydroxyethylcellulose (part)               --   --    --   --    --   --    --   --SBR latex (part)    --   --    --   10    10   10    10   10Acrylic latex (part)               10   10    10   --    --   --    --   --Tg of latex (               +25  +25   +25  +20   +5   -10   -45  -45Solid concentration (%)               35Coating weight (g/m.sup.2)               8Undulation after printing               A    A     B    A     A    A     B    BCurl 52040Pick resistance     B    B     B    A     A    A     A    ABlocking            A    A     A    A     A    A     B    ACalendering linear pressure (kg/cm)               200__________________________________________________________________________                Example                      Example                            Example                                  Example                                        Example                                              Example                                                    Example                9     10    11    12    13    14    15__________________________________________________________________________[Support]LBKP (part)NBKP (part)Pigment (part)Precipitated calcium carbonate (part)Ground calcium carbonate (part)Talc (part)Alkyl ketene dimer (part)Cationic acrylamide (part)Cationized starch (part)Aluminum sulfate (part)Basis weight (g/m.sup.2)[Ink-receiving layer]Synthetic amorphous silica (part)PVA 117 (part)Cationic dye fixer (part)Solid concentration (%)Coating weight (g/m.sup.2)Coating method[Backcoat layer]Kaolin (part)Equilibrium moisture content of pigmentSilanol group containing PVA (part)                5     5     3     3     5     5     --Polyvinyl alcohol.sup.1) (part)                --    --    --    --    --    --    5Oxidized starch (part)                --    --    --    --    --    --    --Phosphate esterified starch (part)                --    --    2     2     --    --    --Carboxymethylcellulose (part)                1     --    --    1     --    --    --Hydroxyethylcellulose (part)                --    1     --    --    --    --    --SBR latex (part)     10    10    10    10    10    10    10Acrylic latex (part) --    --    --    --    --    --    --Tg of latex (                +20   +20   +20   +20   -40   -50   +20Solid concentration (%)Coating weight (g/m.sup.2)Undulation after printing                A     A     A     A     A     B     ACurl 52040Pick resistance      A     A     A     A     A     A     BBlocking             A     A     A     A     A     B     ACalendering linear pressure (kg/cm)__________________________________________________________________________
TABLE 2__________________________________________________________________________               Comp.                    Comp.                         Comp.                              Comp.                                   Comp.                                        Comp.               Example                    Example                         Example                              Example                                   Example                                        Example               1    2    3    4    5    6__________________________________________________________________________[Support]LBKP (part)         80NBKP (part)         20Pigment (part)      25Precipitated calcium carbonate (part)               7.5Ground calcium carbonate (part)               8.75Talc (part)         8.75Alkyl ketene dimer (part)               0.10Cationic acrylamide (part)               0.03Cationized starch (part)               0.8Aluminum sulfate (part)               0.4Basis weight (g/m.sup.2)               90[Ink-receiving layer]Synthetic amorphous silica (part)               100PVA 117 (part)      50Cationic dye fixer (part)               20Solid concentration (%)               13Coating weight (g/m.sup.2)               8Coating method      Airknife[Backcoat layer]Kaolin (part)       100Equilibrium moisture content of pigment               1.2% by               weightSilanol group containing PVA (part)               5    5    5    5    --   10Oxidized starch (part)               --   --   --   --   --   10Phosphate esterified starch (part)               --   --   --   --   --   --Carboxymethylcellulose (part)               --   --   --   --   --   --Hydroxyethylcellulose (part)               --   --   --   --   --   --SBR latex (part)    10   10   --   10   --   --Acrylic latex (part)               --   --   10   --   30   --Tg of latex (               -60  +40  +45  +80  +45  --Solid concentration (%)               35Coating weight (g/m.sup.2)               8Undulation after printing               B    A    A    C    C.sup.2)                                        ACurl 52040Pick resistance     A    C    C    C    A    CBlocking            C    A    A    A    A    ACalendering linear pressure (kg/cm)               200__________________________________________________________________________ Note: .sup.2) Waviness of grade C occurred before printing.
EXAMPLE 16 A support was produced by mixing 100 parts of a wood pulp comprising 80 parts of LBKP (freeness: 400 ml csf) and 20 parts of NBKP (freeness: 450 ml csf) with 25 parts of pigments comprising precipitated calcium carbonate/ground calcium carbonate/talc (30/35/35), 0.10 part of commercially available alkyl ketene dimer, 0.03 part of commercially available cationic acrylamide, 0.8 part of commercially available cationized starch and 0.4 part of aluminum sulfate and making the mixture into a paper of 90 g/m.sup.2 in basis weight by a Fourdrinier paper machine to obtain a support.
An ink-receiving layer was provided in the following manner. A coating composition for ink-receiving layer comprising 100 parts of a synthetic amorphous silica (Finesil X37B manufactured by Tokuyama Soda Co., Ltd.), 50 parts of polyvinyl alcohol (PVA 117 manufactured by Kuraray Co., Ltd.) and 20 parts of a cationic dye fixer (Sumirase Resin 1001 manufactured by Sumitomo Chemical Co., Ltd.) was prepared. The resulting coating composition had a solid concentration of 13%. The coating composition was coated on the front side of the support at a coating weight of 10 g/m.sup.2 by an air knife coater.
Furthermore, a backcoat layer was provided on another side of the support in the following manner. 100 parts of a pigment having an equilibrium moisture content of 4.9% by weight (hydrated halloysite KA Press manufactured by Oharu Kagaku Co.) was dispersed with 0.4 part of commercially available sodium polyacrylate and to the dispersion were added 5 parts of a silanol group containing polyvinyl alcohol (R Polymer 1130 manufactured by Kuraray Co., Ltd.) and 15 parts (solid content) of a styrene-butadiene latex (0693 manufactured by Japan Synthetic Rubber Co., Ltd.) to prepare a coating composition of 35% in solid concentration for backcoat layer. The resulting coating composition was coated at a coating weight of 8 g/m.sup.2 on the opposite side to the ink-receiving layer side and subjected to calendering treatment to obtain an ink jet recording sheet.
EXAMPLE 17 The support and the ink-receiving layer were obtained in the same manner as in Example 16. The coating composition for the backcoat layer was prepared in the same manner as in Example 16 except that 50 parts of the pigment used in Example 16 and 50 parts of a pigment having an equilibrium moisture content of 1.2% by weight (Delaminated clay; Nuclay manufactured by Engelhard Co.) were used in combination as the pigment. The resulting coating composition was coated in the same manner as in Example 16, followed by calendering treatment to obtain an ink jet recording sheet.
EXAMPLE 18 The support and the ink-receiving layer were obtained in the same manner as in Example 16. The coating composition for the backcoat layer was prepared in the same manner as in Example 16 except that 20 parts of the pigment used in Example 16 and 80 parts of a pigment having an equilibrium moisture content of 1.2% by weight (No. 2 clay; Hydrasperse manufactured by Huber Corp.) were used in combination as the pigment. The resulting coating composition was coated in the same manner as in Example 16, followed by calendering treatment to obtain an ink jet recording sheet.
EXAMPLE 19 The support and the ink-receiving layer were obtained in the same manner as in Example 16. The coating composition for the backcoat layer was prepared in the same manner as in Example 16 except that 90 parts of the pigment used in Example 16 and 10 parts of a pigment having an equilibrium moisture content of 0.3% by weight (ground calcium carbonate; Softon 2200 manufactured by Bihoku Funka Kogyo Co.) were used in combination as the pigment. The resulting coating composition was coated in the same manner as in Example 16, followed by calendering treatment to obtain an ink jet recording sheet.
EXAMPLE 20 The support and the ink-receiving layer were obtained in the same manner as in Example 16. The coating composition for the backcoat layer was prepared in the same manner as in Example 16 except that 90 parts of a pigment having an equilibrium moisture content of 5.9% by weight (hydrated halloysite; NAG manufactured by Shinshu Kaolin Co.) and 10 parts of a pigment having an equilibrium moisture content of 0.3% by weight (ground calcium carbonate; Softon 2200 manufactured by Bihoku Funka Kogyo Co.) were used in combination as the pigment. The resulting coating composition was coated in the same manner as in Example 16, followed by calendering treatment to obtain an ink jet recording sheet.
EXAMPLE 21 The support and the ink-receiving layer were obtained in the same manner as in Example 16. The coating composition for the backcoat layer was prepared in the same manner as in Example 16 except that 100 parts of a pigment having an equilibrium moisture content of 5.9% by weight (hydrated halloysite; NAG manufactured by Shinshu Kaolin Co.) was used as the pigment. The resulting coating composition was coated in the same manner as in Example 16, followed by calendering treatment to obtain an ink jet recording sheet.
EXAMPLE 22 The support and the ink-receiving layer were obtained in the same manner as in Example 16. The coating composition for the backcoat layer was prepared in the same manner as in Example 16 except that 10 parts of a pigment having an equilibrium moisture content of 5.9% by weight (hydrated halloysite; NAG manufactured by Shinshu Kaolin Co.) and 90 parts of a pigment having an equilibrium moisture content of 0.3% by weight (ground calcium carbonate; Softon 2200 manufactured by Bihoku Funka Kogyo Co.) were used in combination as the pigment. The resulting coating composition was coated in the same manner as in Example 16, followed by calendering treatment to obtain an ink jet recording sheet.
The specimen sheets (A4 size) obtained in the following Examples and Comparative Examples were allowed to stand under each of the three conditions: 5 90% RH. Thereafter, the sheets were placed on a flat table and heights (H) of curls at the four corners of the sheet were measured. The relative change in height of curl is a difference between the height of the curl after having undergone the 20 (H.sub.M) and same after having undergone the other conditions. The relative change in height of curl after having undergone the 5 10% RH and 40 H.sub.H respectively, to which plus (+) and minus (-) is suffixed depending on the curl directions, towards the ink-receiving layer side and towards the backcoat layer side, respectively. If each of the measures, H.sub.L, H.sub.H and H.sub.L -H.sub.H, fails to fall within .+-.10 (mm), the specimen sheet under this test is determined unsuccessful.
TABLE 3__________________________________________________________________________              Example                   Example                        Example                             Example                                  Example                                       Example                                            Example              16   17   18   19   20   21   22__________________________________________________________________________[Support]LBKP (part)        80NBKP (part)        20Pigment (part)     25Precipitated calcium carbonate (part)              7.5Ground calcium carbonate (part)              8.75Talc (part)        8.75Alkyl ketene dimer (part)              0.10Cationic acrylamide (part)              0.03Cationized starch (part)              0.8Aluminum sulfate (part)              0.4Basis weight (g/m.sup.2)              90Ash content (%)    17.9[Ink-receiving layer]Synthetic amorphous silica (part)              100PVA 117 (part)     50Cationic dye fixer (part)              20Solid concentration (%)              13Coating weight (g/m.sup.2)              10Coating method     Airknife[Backcoat layer]Hydrated halloysite KA (part)              100  50   20   90   --   --   --Hydrated halloysite NGA (part)              --   --   --   --   90   100  100Delaminated clay (part)              --   50   --   --   --   --   --No. 2 clay (kaolin) (part)              --   --   80   --   --   --   --Ground calcium carbonate (part)              --   --   --   10   10   --   90Average equilibrium moisture content              4.9  3.1  1.9  4.4  5.3  5.9  0.9of pigment (wt %)Sodium polyacrylate (part)              0.4Silanol group containing PVA (part)              5SBR latex 0693 (part)              15Tg of latex (              +20Solid concentration (%)              35Coating weight (g/m.sup.2)              8Relative change in height of curl (mm)HL                 -4   +5   +9   -1   -6   -17  +20HH                 +1   0    -1   +1   +1   0    -3HH-HL (mm)         +5   -5   -10  +2   +7   +17  -23Calendering linear pressure (kg/cm)              200__________________________________________________________________________
The change of H.sub.H, H.sub.L and H.sub.H -H.sub.L with the average equilibrium moisture content of the pigments in Examples 16-22 is shown in FIG. 1 and FIG. 2.
EXAMPLES 23-28 Ink jet recording sheets were obtained in the same manner as in Example 16 except that amount (solid) of the styrene-butadiene latex in the backcoat layer was 2 parts, 5 parts, 30 parts, 60 parts or 70 parts in place of 15 parts as shown in Table 4.
TABLE 4__________________________________________________________________________               Example                    Example                         Example                              Example                                   Example                                        Example               23   24   25   26   27   28__________________________________________________________________________[Support]LBKP (part)         80NBKP (part)         20Pigment (part)      25Precipitated calcium carbonate (part)               7.5Ground calcium carbonate (part)               8.75Talc (part)         8.75Alkyl ketene dimer (part)               0.10Cationic acrylamide (part)               0.03Cationized starch (part)               0.8Aluminum sulfate (part)               0.4Basis weight (g/m.sup.2)               90Ash content (%)     17.9[Ink-receiving layer]Synthetic amorphous silica (part)               100PVA 117 (part)      50Cationic dye fixer (part)               20Solid concentration (%)               13Coating weight (g/m.sup.2)               10Coating method      Airknife[Backcoat layer]Hydrated halloysite KA (part)               100Equilibrium moisture content of pigment               4.9(wt %)Sodium polyacrylate (part)               0.4Silanol group containing PVA (part)               5SBR latex 0693 (part)               2    5    15   30   60   70Tg of latex (               +20Solid concentration (%)               35Coating weight (g/m.sup.2)               8Relative change in height of curl (mm)HL                  -5   -5   -4   -1   +1   +2HH                  +1   +1   +1   -4   -9   -13HH-HL (mm)          +6   +6   +5   -3   -10  -15Pick resistance of backcoat layer               C    B    A    A    A    ACalendering linear pressure (kg/cm)               200__________________________________________________________________________
EXAMPLES 29-34COMPARATIVE EXAMPLE 7 Ink jet recording sheets were obtained in the same manner as in Example 16 except that the coating amount of the backcoat layer was changed as shown in Table 5.
TABLE 5__________________________________________________________________________               Comp.               Example                     Example                           Example                                Example                                     Example                                          Example                                               Example               7     29    30   31   32   33   34__________________________________________________________________________[Support]LBKP (part)         80NBKP (part)         20Pigment (part)      25Precipitated calcium carbonate (part)               7.5Ground calcium carbonate (part)               8.75Talc (part)         8.75Alkyl ketene dimer (part)               0.10Cationic acrylamide (part)               0.03Cationized starch (part)               0.8Aluminum sulfate (part)               0.4Basis weight (g/m.sup.2)               90Ash content (%)     17.9[Ink-receiving layer]Synthetic amorphous silica (part)               100PVA 117 (part)      50Cationic dye fixer (part)               20Solid concentration (%)               13Coating weight (g/m.sup.2)               10 [WI]Coating method      Airknife[Backcoat layer]Hydrated halloysite KA (part)               100Equilibrium moisture content of pigment               4.9% by               weightSodium polyacrylate (part)               0.4Silanol group containing PVA (part)               5SBR latex 0693 (part)               15Tg of latex (               +20Solid concentration (%)               35Coating weight (g/m.sup.2)               0     1     3    8    15   25   35WB-WI (g/m.sup.2)   -10   -9    -7   -2   +5   +15  +25Relative change in height of curl (mm)HL                  +42   +20   +8   -4   -6   -9   -9HH                  Cylindrical                     Cylindrical                           +10  +1   +1   +1   +1HH-HL (mm)          +large                     +large                           +2   +5   +7   +10  +10Calendering linear pressure (kg/cm)               200__________________________________________________________________________
It can be seen from Table 5 that ink jet recording sheets excellent in curling resistance can be obtained when the coating amount W.sub.B of the backcoat layer is 3 g/m.sup.2 or more and the difference between the coating amount of the backcoat layer and that of the ink-receiving layer (W.sub.B -W.sub.I) is -10 to 25 g/m.sup.2.
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