JP2010150696A - Coated white paperboard - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated white paperboard obtained by applying a coating liquid on a stock paper laminated by ≥two layers, drying and then glossiness-finishing with a gloss calendar or soft calendar treatment, having less fine gloss unevenness and excellent in surface quality even by the gloss calendar or soft calendar treatment at a high temperature, having a high 75 degree ISO glossiness on the white coated paper surface and also excellent in process aptitude such as pasting with glue, etc. <P>SOLUTION: This coated white paperboard is obtained by coating the coating liquid containing styrene-butadiene-based copolymer latex having ≥2.5 ratio (median diameter/d50) of the median diameter obtained by a laser method particle size distribution measurement to the mean particle diameter d50 obtained by a precipitation method particle size distribution measurement, also containing 35 to 80 mass% de-laminated kaolin having ≥38% volume distribution of the particles having ≤1 μm, obtained by the laser method particle size distribution measurement, and ≥30 mass% butadiene content in used monomers, drying and then treating with the gloss-calendaring or soft-calendaring at ≥115°C high temperature for imparting the glossiness. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a coated white paperboard which is coated with a coating liquid on a base paper laminated with two or more layers, dried and then gloss-finished with a gloss calendar or a soft calendar.

  The coated white paperboard is mainly used for a paper container such as a decorative box and a gift case box or a book cover. In these applications, coated white board with little unevenness of glossiness from the viewpoint of cosmetics, excellent surface texture, that is, surface quality, high 75 degree ISO glossiness of white paper coated surface, and excellent processing suitability such as adhesive pasting Paper is required.

  In the production of coated white paperboard, from the viewpoints of labor saving, space saving, productivity, etc., many methods have been used in the past, including base paper making, coating, drying, and calendering. Glossy finishes with gloss calenders or soft calenders that are treated with

  However, in the gloss calendar or soft calendar process, the basis weight unevenness, the coating amount unevenness, etc. tend to appear as minute unevenness, resulting in a loss of cosmetic properties. When the treatment temperature is high, the surface of the coating layer is softened and crushed, so that minute gloss unevenness due to pigment orientation unevenness becomes remarkable. In order to solve this problem, an improvement in trapping unevenness that is considered to be caused by uneven gloss has been proposed by a method of applying a light vapor immediately before soft calendering at a high temperature (see, for example, Patent Document 1). .

  In addition, calcium carbonate is added to the top coat from 65 to 80% by mass with respect to the total pigment, and the butadiene content in the monomer used is 20 to 40% by mass and the styrene / butadiene copolymer latex having an average particle size of 50 to 100 nm is contained. The coating liquid which performs is proposed (for example, refer patent document 2).

  Conventionally, delaminated kaolin has been used as a pigment used in the coating layer (see, for example, Patent Document 4), and a coated white paperboard containing delaminated kaolin in the undercoat layer of the coating layer has been proposed. (For example, see Patent Documents 3 and 5).

In the above-mentioned conventional coated white paperboard, even if a slight vapor is applied just before the soft calendering process at a high temperature, a sufficient effect cannot be obtained for the improvement of the minute gloss unevenness. In addition, since the unevenness of the base paper made by laminating two or more layers is often inferior to that of a single-layer paper base paper, the coated white paper board is more likely to cause minute gloss unevenness than the coated paper, and is sufficient. It is also difficult to obtain 75 degree ISO glossiness of the white paper coated surface. Furthermore, the styrene-butadiene copolymer latex with a high butadiene content has high film-forming properties, so that the shrinkage during drying is large and the orientation of the pigment is easily disturbed. If the gloss calender or soft calender process is performed at a high temperature in order to increase the 75 degree ISO glossiness of the white paper coated surface, minute gloss unevenness tends to occur, which is a problem. In addition, in a coating layer containing delaminated kaolin, processing suitability such as reduction in unevenness of fine gloss and pasting of glue cannot be sufficiently obtained, and therefore, improvement thereof is demanded.
JP-A-4-370298 Japanese Patent No. 3082188 JP 2002-363877 A JP 2006-9184 A JP 2007-254914 A

  The present invention relates to a styrene / butadiene-based copolymer having a high butadiene content with respect to a coated white paperboard that has been coated with a coating liquid on a base paper laminated with two or more layers, dried, and then finished with gloss calender or soft calender. Using a coating solution containing a binder containing a combined latex and a pigment containing a delaminated kaolin as a main component, and even at a high temperature gloss calendering treatment, there is little fine gloss unevenness and excellent surface quality. It is intended to realize a coated white paperboard having a high ISO glossiness and excellent processing suitability such as adhesive pasting.

  In order to achieve the above object, the present invention provides a coated white board made by coating two or more layers of a coating liquid containing a pigment and a binder as main components. A delaminated kaolin having a ratio (median diameter / d50) to an average particle diameter d50 by particle size distribution measurement of 2.5 or more and a volume distribution of particles of 1 μm or less by laser method particle size distribution measurement of 38% or more. 115 ° C. or higher after coating and drying a coating liquid containing a styrene / butadiene copolymer latex having 35 to 80% by mass of the total pigment and a butadiene content of 30% by mass or more in the monomers used. It is glossed by processing with a gloss calendar or a soft calendar at a high temperature.

  The coated white paperboard according to the present invention includes a case where it is formed by applying a coating liquid containing 3% by mass or more of a plastic pigment as the pigment to the uppermost layer.

  In another embodiment, in the coated white paperboard, the 75 ° ISO glossiness of the white paper coated surface specified in JIS P 8142: 2005 “Method for measuring 75 ° specular gloss” is 50% or more. It is.

    In another embodiment, coated white paperboard is coated on both sides.

  By adopting the structure of the present invention, after coating and drying the coating liquid, the coated white paperboard having a glossy finish with a gloss calender or soft calender has excellent surface quality with little micro unevenness of gloss, A coated white paperboard having a high 75 degree ISO glossiness and excellent processability such as glue application is obtained. The rationale for obtaining such an effect is not necessarily clear, but by containing a delaminated kaolin having a specific particle size distribution in the coating solution of the uppermost layer of coated white paperboard coated with two or more layers It is believed that uniform coating and orientation of the pigment on the surface is achieved. As a result, a 75-degree ISO glossiness of a white paper coated surface with a small amount of uneven glossiness can be obtained.

  Even if the coating liquid of the uppermost layer contains a styrene-butadiene copolymer latex having a high butadiene content that is excellent in processing suitability such as adhesive pasting but shrinks during drying and disturbs the orientation of the pigment, Contains specific delaminated kaolin to maintain uniform pigment coverage and orientation on the surface, and 75 ° ISO gloss on blank coated surfaces sufficient without excessive heating due to gloss calendering or soft calendering Therefore, it is difficult for micro gloss unevenness to occur.

  Further, by including a plastic pigment in the uppermost coating liquid, a high 75 degree ISO glossiness of a blank paper coated surface can be obtained. Further, since the plastic pigment is contained, a sufficient 75 degree ISO glossiness of the white paper coated surface can be obtained without excessively high temperature due to the processing of the gloss calender or soft calender, so that minute gloss unevenness hardly occurs.

  As described above, the coated white paperboard of the present invention is coated with a coating liquid, dried, and then glossy finished with a gloss calender or soft calender, has little gloss unevenness and excellent surface quality, and is 75 degrees on the white paper coated surface. A coated white paperboard having a high ISO glossiness and excellent processability such as glue application can be provided.

  In the present invention, two or more layers of a coating liquid containing a pigment and a binder as main components are coated, dried, and then coated on a white paperboard that is subjected to gloss calendering or soft calendering. The ratio (median diameter / d50) between the median diameter by the method particle size distribution measurement and the average particle diameter d50 by the precipitation method particle size distribution measurement is 2.5 or more, preferably 3.0 to 10.0, particularly preferably 3.0 to 8.5 or less, the volume distribution of particles of 1 μm or less by laser method particle size distribution measurement is 38% or more, preferably 42% to 95%, particularly preferably 40 to 85% of delaminated kaolin 35 to 80 of all pigments. It is necessary to contain it by mass%, preferably 40 to 75 mass%, particularly preferably 43 to 73 mass%. The ratio of the median diameter by laser method particle size distribution measurement of delaminated kaolin to the average particle size d50 by sedimentation method particle size distribution measurement (median diameter / d50) is less than 2.5 and / or 1 μm or less by laser method particle size distribution measurement. When the volume distribution of the particles is less than 38%, the fine gloss unevenness and / or the 75 ° ISO glossiness of the white paper coated surface is inferior, and when the content is less than 35% by weight, the fine gloss unevenness and / or the white paper coated surface is poor. When the 75-degree ISO glossiness is inferior and more than 80% by mass, the processing suitability such as paste application is inferior. It is necessary to contain a styrene / butadiene copolymer latex having a butadiene content of 30 to 50% by mass, particularly preferably 32 to 48% by mass, in the monomer used. When the content of butadiene in the monomer used is less than 30% by mass, the processability such as paste application is inferior. In addition, the ratio of the median diameter by the laser particle size distribution measurement to the average particle diameter d50 by the sedimentation particle size distribution measurement (median diameter / d50) exceeds 10.0 and / or particles of 1 μm or less by the laser particle size distribution measurement If the volume distribution exceeds 95%, a problem of poor post-processing suitability such as adhesive pasting tends to occur. Furthermore, when the butadiene content exceeds 50% by mass, there is a problem that micro gloss unevenness and / or 75 degree ISO gloss of the white paper coated surface is inferior.

  Further, by containing 3% by mass or more, preferably 3 to 30% by mass, and particularly preferably 5 to 25% by mass of the plastic pigment as the pigment of the uppermost coating liquid, it is possible to reduce fine gloss unevenness and / or. A 75 degree ISO glossiness of a high white paper coated surface is obtained. If it is less than 3% by mass, the effect is poor. In addition, the effect is increased by increasing the content, but it is determined each time depending on the quality required in consideration of cost, operability, etc., but the cost required even if it exceeds 30% by mass The effect on the surface is poor, and operability problems such as a deterioration in coating property and an increase in dusting in calendar processing after coating are likely to occur.

  In the present invention, the gloss calender or soft calender treatment needs to be performed at a metal roll temperature of 115 ° C. or higher, preferably 120 to 250 ° C., particularly preferably 130 to 200 ° C. When the temperature is lower than 115 ° C., the micro gloss unevenness tends to be improved, but the improvement of the 75 ° ISO glossiness of the white paper coating surface is insufficient, and the nip number is obtained when trying to obtain a sufficient 75 ° ISO glossiness of the white paper coating surface. Therefore, the benefits of saving labor and space are reduced. Moreover, when it exceeds 250 degreeC, problems, such as a fall of whiteness and an increase in dusting, will arise easily.

  Further, the 75 ° ISO glossiness of the blank paper coated surface specified in JIS P 8142 of the coated surface is 50% or more, preferably 55% or more. If the 75 ° ISO glossiness of the white paper coating surface is less than 50%, the glossy calendering or soft calendering process can be performed at a low temperature, so that minute gloss unevenness hardly occurs.

  Next, specific examples of preferred forms of the drug used in the present invention will be specifically described.

  Other pigments used in the coating solution used in the present invention include delaminated kaolin, kaolin, calcined kaolin, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, silica, aluminum hydroxide outside the above range. , Satin white, diatomaceous earth, white carbon and the like, which are usually known as pigments for paper coating, can be used as appropriate.

  The styrene / butadiene copolymer latex used in the coating solution used in the present invention contains styrene and butadiene as monomers, and other monomers are copolymerized as necessary, or the copolymer is modified by chemical reaction. It is a copolymer latex commonly used for paper coating. As other monomers, vinyl monomers such as acrylic acid, methacrylic acid, acrylic acid or alkyl esters of methacrylic acid, acrylonitrile, maleic acid, fumaric acid, and vinyl acetate are often used. In addition to the styrene / butadiene copolymer latex, binders other than styrene / acrylic, vinyl acetate / acrylic, butadiene / methyl methacrylic copolymer latex, oxidized starch, phosphate esterified starch, It can be suitably used from starches such as hydroxyethylated starch, proteins such as casein and soybean protein, and other water-soluble binders such as polyvinyl alcohol.

  In the coating liquid of the present invention, various auxiliaries blended in a normal coating liquid such as a dispersant, a thickener, a water retention agent, an antifoaming agent, a water-resistant agent, and a colorant may be appropriately used.

  The undercoat coating liquid is not particularly limited, and can be appropriately selected depending on the quality design of the coated white paperboard. That is, as a coating liquid composition, the coating liquid which has as a main component the pigment and adhesive agent which are generally used in the coating white paperboard field | area is used. Examples of the pigment include kaolin, delaminated kaolin, calcined kaolin, light calcium carbonate, heavy calcium carbonate, titanium dioxide, talc, silica, aluminum hydroxide, satin white, diatomaceous earth, and white carbon. Examples of adhesives include styrene / butadiene, styrene / acrylic, vinyl acetate / acrylic, butadiene / methylmethacrylate, and other copolymers, latex, oxidized starch, phosphate esterified starch, hydroxyethylated, etc. Examples thereof include starches such as starch, proteins such as casein and soybean protein, and other aqueous adhesives such as polyvinyl alcohol. Moreover, you may use various adjuvants, such as a dispersing agent, a thickener, a water retention agent, an antifoamer, a water-resistant agent, and a coloring agent as needed. Any of these may be used alone or in combination of two or more as required.

As the base paper of the present invention, a base paper laminated in two or more layers used in the production of a conventional coated white paperboard can be used without any particular limitation. For example, a multilayer paperboard having a basis weight of about 100 to 800 g / m ² is used. be able to. More preferably, the basis weight is 120 to 600 g / m ² . In addition, the pulp used for the base paper can be the pulp normally used for coated white paperboard, such as chemical pulp, mechanical pulp, and used paper pulp. Furthermore, as a filler internally added to the base paper, a filler usually used for coated white paperboard can be used, for example, talc, light calcium carbonate, heavy calcium carbonate, kaolin, calcined kaolin, delaminated kaolin, titanium dioxide, silica. , White carbon, diatomaceous earth, aluminum hydroxide, etc. In addition, for the base paper, chemicals used for normal coated whiteboard base paper making such as a yield improver, drainage improver, sizing agent, paper strength improver, and colorant may be used as appropriate.

The coating method is not particularly limited, and two or more layers are coated using various ordinary coating apparatuses such as a blade coater, a rod coater, an air knife coater, and a roll coater. Although there is no restriction | limiting in particular also about the coating amount, 3-35 g / m < ² > is preferable by solid content for each layer. More preferably 5 to 20 g / ^{m 2.} It is dried after each layer is applied or after two or more layers are applied.

  After being coated and dried, it is finished with a gloss calendar or a soft calendar. The gloss calender or soft calender is preferably 2 to 6 nips, particularly 4 nips in consideration of ease of paper feeding and space saving. In the elastic roll, a steel core is covered with synthetic rubber or synthetic resin, and a chilled roll, a steel roll, or the like is used as the metal roll.

  Next, the effects of the present invention will be described in more detail using examples, but the present invention is not limited thereto. In addition, "part" in an Example is a mass part with respect to 100 mass parts of all pigments.

[Example 1]
After coating each of the coating liquids described below on a multilayer paperboard with a basis weight of 200 g / m ² and drying, it is glossed with a 4-nip gloss calender with a metal roll temperature of 130 ° C., and the coated white paperboard Created.

The undercoat coating solution was adjusted to contain 30 parts by weight of kaolin, 30 parts by weight of heavy calcium carbonate, 15 parts by weight of styrene / butadiene copolymer latex, and 3 parts by weight of phosphate esterified starch. / M ² (dry mass) was applied to both sides.

As the top coating liquid for the uppermost layer, the ratio of the median diameter by the laser particle size distribution measurement to the average particle diameter d50 by the sedimentation particle size distribution measurement (median diameter / d50) is 3.6, and the laser particle size distribution measurement 65 parts by weight of delaminated kaolin (trade name: Contour Extreme, manufactured by Imeris) with a volume distribution of particles of 1 μm or less by 1 μm or less, 35% by weight of light calcium carbonate, and styrene with a butadiene content of 40% in the monomer used -Prepared to contain 15 parts by weight of butadiene copolymer latex, 2 parts by weight of phosphoric acid esterified starch, and 0.5 parts by weight of calcium stearate, and 10 g / m ² (dry weight) on one side on each side with an air knife coater Coated.

[Example 2]
When preparing the top coat coating solution for the uppermost layer, a coated white paperboard was prepared in the same manner as in Example 1 except that a styrene / butadiene copolymer latex having a butadiene content of 32% by mass in the monomer used was used. did.

[Example 3]
When preparing the topcoat coating solution for the uppermost layer, a coated white paperboard was prepared in the same manner as in Example 1 except that a styrene / butadiene copolymer latex having a butadiene content of 48% by mass in the monomer used was used. did.

[Example 4]
When adjusting the topcoat coating solution for the uppermost layer, the ratio of the median diameter by laser particle size distribution measurement to the average particle diameter d50 by sedimentation particle size distribution measurement (median diameter / d50) is 3.6, and the laser Ratio of 50 parts by mass of delaminated kaolin (trade name: Contour Extreme, manufactured by Imeris Co., Ltd.) having a volume distribution of particles of 1 μm or less by a method particle size distribution measurement of 51%, 40 parts by mass of light calcium carbonate, 10 parts by mass of plastic pigment A coated white paperboard was prepared in the same manner as in Example 1 except that

[Comparative Example 1]
When adjusting the topcoat coating solution for the uppermost layer, the ratio of the median diameter by laser particle size distribution measurement to the average particle diameter d50 by sedimentation particle size distribution measurement (median diameter / d50) is 3.6, and the laser Implemented except that the volume distribution of particles of 1 μm or less as measured by the method particle size distribution was 30% by weight of delaminated kaolin (trade name: Contour Extreme, manufactured by Imeris Co.) of 51% and 70 parts by weight of light calcium carbonate. Coated white paperboard was prepared as in Example 1.

[Comparative Example 2]
When adjusting the topcoat coating solution for the uppermost layer, the ratio of the median diameter by laser particle size distribution measurement to the average particle diameter d50 by sedimentation particle size distribution measurement (median diameter / d50) is 3.6, and the laser Coating in the same manner as in Example 1 except that the volume distribution of particles having a particle size of 1 μm or less measured by the method particle size distribution was 100% by weight of delaminated kaolin (trade name: Contour Extreme, manufactured by Imeris Co., Ltd.) with 51%. White paperboard was made.

[Comparative Example 3]
When adjusting the topcoat coating solution for the uppermost layer, the ratio of the median diameter by laser particle size distribution measurement to the average particle diameter d50 by sedimentation particle size distribution measurement (median diameter / d50) is 8.6, and laser Except that the volume distribution of particles with a particle size of 1 μm or less measured by the method particle size distribution is 18% delaminated kaolin (trade name: Contour 1500, manufactured by Imeris Co.) 65 parts by mass and light calcium carbonate 35 parts by mass Coated white paperboard was prepared as in Example 1.

[Comparative Example 4]
When adjusting the topcoat coating solution for the uppermost layer, the ratio of the median diameter by laser particle size distribution measurement to the average particle diameter d50 by sedimentation particle size distribution measurement (median diameter / d50) is 9.2. Except that the volume distribution of particles having a particle size of 1 μm or less measured by the method particle size distribution is 12% delaminated kaolin (trade name: Astra Plate, manufactured by Imeris) 65 parts by mass and light calcium carbonate 35 parts by mass A coated white paperboard was prepared in the same manner as in 1.

[Comparative Example 5]
When adjusting the topcoat coating solution for the uppermost layer, the ratio of the median diameter by the laser particle size distribution measurement to the average particle diameter d50 by the sedimentation particle size distribution measurement (median diameter / d50) is 1.6. Example 1 except that the volume distribution of particles having a particle size of 1 μm or less as measured by the method particle size distribution is 94% kaolin (trade name: DB Glaze, manufactured by Imeris Co., Ltd.) 65 parts by mass and light calcium carbonate 35 parts by mass. Coated white paperboard was prepared.

[Comparative Example 6]
When adjusting the topcoat coating solution for the uppermost layer, the ratio of the median diameter by laser particle size distribution measurement to the average particle diameter d50 by sedimentation particle size distribution measurement (median diameter / d50) is 3.2, and the laser The volume distribution of particles of 1 μm or less as measured by the method particle size distribution measurement is the same as in Example 1 except that the volume distribution is 65% by weight of kaolin (trade name: Capim DG, manufactured by Imeris Co.) and 35 parts by weight of light calcium carbonate. Coated white paperboard was prepared.

[Comparative Example 7]
When preparing the topcoat coating solution for the uppermost layer, a coated white paperboard was prepared in the same manner as in Example 1 except that a styrene / butadiene copolymer latex having a butadiene content of 28% by mass in the monomer used was used. did.

[Comparative Example 8]
A coated white paperboard was prepared in the same manner as in Example 1 except that the metal roll temperature of the gloss calendar was 105 ° C.

[Quality evaluation test method]
Each coated white paperboard produced by Examples and Comparative Examples was evaluated.
1) Median diameter by laser method particle size distribution measurement and volume distribution of particles of 1 μm or less: measured by LA920 type manufactured by Horiba, Ltd.
2) Average particle diameter d50 by sedimentation method particle size distribution measurement: Measured with a Sedigraph 5100 manufactured by Micromeritics.
3) ISO glossiness of white paper coated surface: Measured at 75 degrees using a gloss meter manufactured by Murakami Color Research Laboratory according to JIS P8142.
4) Micro gloss unevenness: Visual evaluation was performed in the following four stages.
A: There is no occurrence of unevenness and there is no practical problem.
○: Slight unevenness is observed, but there is no practical problem.
(Triangle | delta): Generation | occurrence | production of unevenness is recognized many and there exists a problem in practical use.
X: The occurrence of unevenness is very large, and there is a problem in practical use.
5) Pasting glue: Applying Lifebond AV-650 (manufactured by Niei Engineering Co., Ltd.) to the coated paperboard surface using a spacer so that the width is 1 mm, the length is 5 mm, and the thickness is 0.1 mm. After stacking so that the backs of the types of paper face each other, 1 kg of mass is pressed over 1 minute, 1 kg of mass is removed, and then left in an environment of temperature 23 ° C. and humidity 50% for 24 hours. Then, it peels off and judges as follows from an adhesion state.
A: The ratio of the area peeled from the base paper layer in the bonded portion is 100%, and there is no practical problem.
○: The ratio of the area peeled from the base paper layer in the bonded portion is less than 100% and 75% or more, and there is no practical problem.
(Triangle | delta): The ratio of the area which has peeled from the base paper layer among the adhesion parts is less than 75% and 50% or more, and there exists a problem practically.
X: The ratio of the area peeled from the base paper layer in the bonded portion is less than 50%, which is problematic in practical use.

  As is apparent from Tables 1 and 2, Examples 1 to 4 have little uneven gloss and high 75 ° ISO gloss on the white paper coated surface, and are excellent in adhesive pasting.

  On the other hand, Comparative Example 1 has a lot of fine gloss unevenness. Comparative Examples 2 and 7 are inferior in glue sticking. In Comparative Examples 3, 4, 6, and 8, the 75-degree ISO glossiness of the white paper coated surface is inferior. In Comparative Example 5, there are many fine gloss unevennesses and paste adhesion is inferior.

  Therefore, the coated white paperboard of the present invention is excellent in surface quality with little micro-gloss unevenness, high in 75 degree ISO glossiness of the white paper coated surface, and excellent in processing suitability such as adhesive pasting.

Claims (4)

  In coated white paperboard, in which two or more layers of coating liquid containing pigment and binder as the main components are coated on the base paper laminated two or more layers, by the median diameter by laser method particle size distribution measurement and by sedimentation method particle size distribution measurement The ratio of the average particle diameter d50 (median diameter / d50) is 2.5 or more, and delaminated kaolin having a volume distribution of particles of 1 μm or less by laser particle size distribution measurement of 38% or more is 35% of all pigments. A coating liquid containing a styrene / butadiene copolymer latex having a butadiene content of 30% by mass or more in the monomer used is coated on the uppermost layer and dried, and then glossed at a high temperature of 115 ° C. or higher. Coated white paperboard, characterized by being glossed by processing with a calendar or soft calendar.   2. The coated white paperboard according to claim 1, wherein a plastic pigment is contained as a pigment of the uppermost layer coating solution in an amount of 3% by mass or more of the total pigment.   The 75 degree ISO glossiness of the white paper coating surface prescribed | regulated to JISP8142: 2005 "Paper and paperboard-the measuring method of a 75 degree specular glossiness" is 50% or more, It is characterized by the above-mentioned Coated white paperboard. The coated white paperboard according to any one of claims 1 to 3, which is coated on both sides.