KR20050086818A - Process for producing super high bulk, light weight coated papers - Google Patents

Abstract

The present invention relates to a process of manufacturing a high bulk, low weight paper product produced by using a high level of groundwood containing sheet, blade coating with specifically formulated coatings then passing the paper web between two extended-nip calenders, one calender for each side of paper. As a result, densification of the resulting coated paper product is reduced, while maintaining stiffness and opacity comparable to heavier weight sheets.

Description

Manufacturing method of ultra-bulk light weight coated paper {PROCESS FOR PRODUCING SUPER HIGH BULK, LIGHT WEIGHT COATED PAPERS}

The present invention uses a high level of wood-containing sheet, coated it with a specially formulated coating, and then used one nip for each side of the paper to apply two wide-nip calendars. A method of making a high bulk lightweight paper product having the same stiffness and opacity as a heavier sheet, including passing a paper web.

As the rates for bulky mailings continue to increase, the demand for lighter papers suitable for use in magazines has increased. However, the lighter the paper, the more problems such as "show-through" and "limp feel" occur, so this lighter paper is practically a magazine, booklet, annual report. , Advertising flyers, direct mail and similar promotions, especially in premium magazines.

By using higher levels of wood and coating paper webs with coatings blended with higher levels of kaolin and plastic pigments or with coatings that tend to be bulkier than conventional coatings, a lightweight high-bulk paper is desired. Attempts have been made. See, for example, US Pat. Nos. 6,287,424, 6,332,953, and 4,749,445. U.S. Pat.No. 5,283,129 discloses a high gloss and light weight coated with a pigment composition comprising delaminated clay, calcined clay and titanium dioxide, where up to about 5 parts by weight of hollow core opaque plastic pigments can replace titanium dioxide. Start the paper. U. S. Patent No. 4,010, 307 discloses a high gloss coated paper product comprising 70 to 95 weight percent calcium carbonate and 5 to 30 weight percent non-film forming polymer pigments having particles of 0.05 to 0.30 microns in size.

In the papermaking process, the finishing operation may be a calendering process that passes the paper web between the nips formed between one or more pairs of rolls to make the surface of the web flat to form a smooth surface. At the same time, the thickness of the paper web, ie the caliper, is reduced and the web becomes dense. Since bulkiness is inversely related to density, as density increases, the bulkiness of finished paper products will decrease. At reduced loading and nip counts, light weight (24 to 40 pounds) using on-line hot soft calender, on-line supercalender or off-line supercalender Further attempts have been made to make high-bulk coated papers. For example, US Pat. Nos. 5,694,837, 5,750,259, 5,546,856, 5,400,707 for devices for finishing continuous paper sheets; US Patent No. 5,163,364 for a method of calendaring paper or cardboard webs; And US patent application Ser. No. 09 / 839,507 on high-bulk paper. Wikstrom, M. "Calendering of coated paper and board in an extended soft nip.Nordic Pulp & Paper Research J. no. 4, p 289-298 (1997)]; Carlsson et al.," Influence of latex binder viscoelastic properties on the high temperature calendering runnability. 2002 TAPPI Coating Conference, p 457; And Moreau-Tabiche et al., “Wood containing paper pilot calendering obtained results through supercalendering, soft nip calendering, and extended nip concept. TAPPI 2000 Coating Conference, p 245].

However, as a result of this attempt to produce lightweight, high-bulk paper using pressures lower than conventional supercalendering nip pressures, 75, typically less than 40, typically less than 35, with low gloss Paper with ° TAPPI glossiness was produced. Such lower gloss papers cannot be used in many publishing applications, such as magazines, where lightweight high-bulk papers with high gloss and good print gloss are required.

Thus, current methods of increasing the bulkiness of paper use higher levels of wood-containing substrates, which are coated with easy-to-finish coatings (combined with higher levels of kaolin and plastic pigments), Supercalendering at reduced payload and nip count. Analysis of the 30 pound sample currently on the market revealed that the bulk of this paper was 1.7 to 1.9 mils.

The prior art does not teach a method of making high-bulk, lightweight coated papers with high stiffness, opacity, and brightness that can be used as "low-end" offset paper. Therefore, there is a great need to develop lighter weight sheets with higher stiffness and opacity compared to heavier sheets.

Summary of the Invention

What was clearly required in the art was to use a high level of wood-containing sheets, blade coated them with specially formulated coatings, and then calendar with two wide-nip calendars with one calendar for each side of the paper. The present invention provides a method of making a 30 pounds / 3300 square feet ultra-bulk lightweight coating paper (LWC), having high stiffness, opacity and whiteness, which can be used as a "low-end" offset paper. Are satisfied by

The data of the inventors of the present invention show that the method of the present invention provides ultra-bulk LWC with bulk properties improved by 22% or less than the highest bulk sheet currently on the market. The wide-nip calendered paper of the present invention exhibits better whiteness and opacity, and equivalent or better printing performance, in particular printing glossiness, than supercalendered counterparts. The use of two wide-nip calendars achieves much higher bulk, mainly due to the better bulk preservation of the wide-nip calendar, ie two wide-nip calendars at the same payload are supercalender and hot. This is because it provides lower nip strength than soft calendars.

Accordingly, it is an object of the present invention to provide a fiber furnish comprising (a) a mechanical furnish comprising mechanical pulp and chemical pulp; (b) forming a paper web from the fiber furnish; (c) removing water from the web; (d) applying the coating formulation of the present invention; (e) calendaring by passing the coated web through the nip of two wide-nip calendars so that each side of the paper is treated with one of the calendar nips opposite the heated roll (each calendaring nip is at least 300 ° F.) Formed by a calender roll having a surface temperature and a backing shoe having a width of at least 30 mm, the nip provides a payload of at least 1000 pounds per linear inch, thereby calendered paper having a caliper retention of more than 75%. It is to provide a method for producing an ultra-bulk-offset lightweight coated paper comprising a).

It is yet another object of the present invention to provide a method of making a 30 pounds / 3300 square feet ultra-bulk No. 5 offset lightweight coated paper.

Another object is to provide a furnish comprising at least 40%, preferably at least 60% mechanical pulp, wherein the mechanical pulp portion is characterized by thermomechanical pulp (TMP) and conventional stone groundwood pulp. Blends blended in equal amounts, the remainder is Kraft.

It is a further object of the present invention to provide a method of making an ultra-bulk offset lightweight coated paper, preferably applying a coating formulation using a blade coater or metering size press.

Another object of the present invention is to provide a coating formulation comprising (i) a hollow plastic pigment; (ii) kaolin pigments; (iii) calcined kaolin clay; (iv) titanium dioxide (TiO ₂ ) pigments; (v) synthetic latex binders; And (vi) a synthetic thickener (or a co-binder comprising a carboxymethylcellulose (CMC) or acrylic acid-based or a mixture based thickener). .

Another object is to provide a coating formulation in which the hollow plastic pigment is present in an amount of at least about 2%, preferably 3 to 5% by weight of the total amount of the pigment.

Another object is that the kaolin pigment is at least about 70% by weight, preferably 80 to 100% by weight of the total amount of the pigment and when counting the particles using a Sedigraph particle size analyzer, at least 85% of the particles are less than 2 microns And having a fine particle size distribution characterized in that at least 50% of the particles are less than 0.5 microns, said kaolin pigments being fine coarse particles having a shape factor greater than 15, preferably 20 to 27. To provide a coating formulation having a platey form.

Another object is to provide a coating formulation wherein the calcined kaolin is at least about 5% by weight of the total amount of pigment.

Another object is to provide a coating formulation in which the TiO ₂ is present in an amount of at least about 2% by weight, preferably 3 to 5% by weight of the total amount of the pigment.

Yet another object is to provide a coating formulation in which the synthetic latex is present at a concentration of at least about 12 parts by weight of the total amount of pigment.

Another object is to provide a coating formulation wherein said synthetic thickener is present at a concentration of at least about 0.05 parts by weight of the total amount of pigment.

Another object is to provide a coating formulation wherein the coating comprises hard calcium carbonate (PCC) or heavy calcium carbonate (GCC).

Another object of the present invention is a weight of at least 2.0 pounds / 3300 square feet, preferably 2.0 to 60 pounds / 3300 square feet, most preferably 2.5 to 5.5 pounds / 3300 square feet per side on each surface of the web. Platelet kaolin pigment, latex binder, having a water content of at least 5.5%, preferably 6.5 to 8.0%, most preferably 7.0%, and forming a coated web with a caliper greater than 2.6 mils prior to calendering And it provides a coating material comprising a thickener.

Another object of the present invention is to provide two wide-nip calenders, preferably about 40 to about 80 mm, at a calendaring temperature adjusted to about 300 to about 430 ° F. and a nip load of 1700 to 2400 pli. A method of making an ultra-bulk offset lightweight coated paper, which uses a Schneb calender (SNC) having a calendering step, while maintaining much more of its original bulk than a traditional supercalender or hot soft calender. will be.

Another object of the present invention is to provide an ultra high-bulk offset lightweight coated paper having a finished coated paper having a basis weight of 28 to 38 pounds / 33 square feet and exhibiting a 75 ° TAPPI gloss of at least 35% and a caliper of at least 2.15 mil It is to provide a manufacturing method.

Yet another object of the present invention is an ultra-bulk offset with LWC showing a caliper 17-27% higher than a caliper of a supercalendered 30 pound / 3300 square foot LWC, with improved whiteness, opacity and print gloss. It is to provide a method for producing a lightweight coated paper.

It is a further object of the present invention that the wide-nip shoe calender improves bulk by 22% or less compared to supercalendered counterparts, not only having better whiteness and opacity, but also comparable or better printing. It is to provide a method for producing an ultra-bulk offset lightweight coated paper, which provides No. 5 LWC offset sheet with performance.

1 is a graph showing the effect of calendaring on caliper performance. This graph shows that paper calendered with a schnip calendar shows a much higher caliper.

2 is a graph showing the effect of calendaring on whiteness performance. This graph shows that the sample finished on the schnip calendar clearly gives higher whiteness than the sample finished on the supercalendar.

3 is a graph showing the effect of paper on opacity performance.

4 is a graph showing the effect of the coating on the gloss performance.

5 is a graph showing Parker Print Surf (PPS) performance. This graph shows that PPS depends not only on the calendering method but also on the type of paper and coating material.

6 is a graph showing the effect of the coating on the printing gloss.

The process of the present invention produces lightweight paper products with relatively high bulk, thereby producing thicker sheets with reduced density or compressibility while maintaining higher stiffness and opacity compared to heavier sheets.

In the process of the present invention, raw paper containing high levels of mechanical pulp is produced. This process further comprises (i) a hollow plastic pigment present in an amount of at least 2% by weight of the total amount of the pigment; (ii) plate- or engineered particle kaolin present in an amount of at least 70% by weight of the total amount of pigment; (iii) TiO ₂ present in an amount of at least 2% by weight of the total amount of the pigment; And (iv) a coating formulation consisting of a pigment containing calcined clay present in an amount of at least 10% by weight of the total amount of pigment. The binder comprises 14-20 parts by weight of the total pigment, acronitrile-modified, bi-modal particle size distribution styrene butadiene (PSD SB) latex or SB latex. Co-binders include thickeners of CMC-based, acrylic acid-based, or mixed substrates thereof. The coating formulation is applied using a blade coater or metering size press to a coating weight of about 2.5 to 5.5 pounds / 3300 square feet. The process of the present invention further comprises a calendering step carried out using two wide-nip calenders with one nip per side so that the coated side of the paper faces the heating roll at a temperature of 320 to 420 ° F. Include. Line loading is about 1400-2600 PLI. The sheet moisture is adjusted to at least about 6.5% before calendering. The resulting paper shows better whiteness and opacity than the supercalendar counterpart. The printing performance is equal to or better than the supercalendered counterpart, especially in print glossiness.

Textile furnish

LWC paper produced using the process of the present invention is based on an aqueous furnish having a high proportion of mechanical pulp and the remaining amount of kraft. Mechanical pulp is generally at least about 40%, usually 40 to 80%, preferably 60 to 80%. The mechanical pulp portion comprises a blend of thermomechanical pulp and conventional stone ground wood pulp in equal amounts. The rest is craft. Mechanical pulp provides a well formed substrate. The term mechanical pulp as used herein may include stone groundwood pulp (SGW), thermomechanical pulp (TMP) and chemical-thermomechanical pulp (CTMP). Sample furnish formulations are (1) 30% TMP / 30% SGW / 40% soft kraft (SWK) and (2) 60% TMP / 10% PGW / 30% SWK. SWK is not considered a mechanical pulp. Another example may be 55% -65% CTMP / 35-45% SWK.

Using a conventional paper machine, a paper sheet is produced from the furnish. The paper sheet then moves to a press, where it can typically be pressed. The web then moves to the drying section and is dried such that the moisture content is less than 6%, preferably 4% or less. The paper may then be coated on or outside the paper machine with the coating formulation of the present invention.

Coating formulation

In the process of the invention, the coating formulation is applied before finishing. Coating formulations according to the invention include (i) hollow plastic pigments; (ii) kaolin pigments; (iii) calcined kaolin clay; (iv) titanium dioxide (TiO ₂ ) pigments; (v) synthetic latex binders; And (vi) synthetic thickeners (or co-binding agents comprising thickeners based on carboxymethylcellulose or acrylic acid-based or mixed thereof). The coating formulation may also include hard calcium carbonate (PCC) or heavy calcium carbonate (GCC).

The hollow plastic pigment is present in an amount of at least 2% by weight, preferably from about 3 to 5% by weight of the total amount of the pigment. Suitable hollow plastic pigments include ROPAQUE HP-1055 (trademark), available from ROHMNOVA, 44305 Akron Gilklist Road 2990, Ohio, USA. The kaolin pigment is at least about 70% by weight, preferably 80 to 100% by weight of the total amount of the pigment, and is preferably operated to have a fine particle size and a very flat form. Kaolin pigments have a fine particle size distribution characterized by at least 85% of the particles being less than 2 microns and at least 50% of the particles being less than about 0.5 microns when the particles are counted using the sedimentation particle size analyzer. The kaolin has a platy morphology characterized by fine coarse particles having a form factor greater than 15, preferably about 20 to 27. Morphological factors are described in Sven Lohmander, "Aspect Ratios Of Pigment Particles Determined By Different Methods," Nordic Pulp And Paper Research, Vol. 15, No. 3/2000, pg. 221. Suitable kaolin pigments include CONTOUR 1500, available from Imerys, 31020 Dry Branch, Georgia, USA. Calcined kaolin clay is at least 5% by weight of the total amount of pigment. Suitable calcined pigments include ANSILEX 93, available from Engelhard, 08830 Iselin Wood Avenue, NJ, USA. The TiO ₂ pigment is present in an amount of at least 2% by weight, preferably about 3 to 5% by weight of the total amount of the pigment. Suitable TiO ₂ pigments include RPS VANTAGE® available from DuPont. The synthetic latex binder is present at a concentration of at least about 12 parts by weight of the total amount of pigment. Suitable synthetic latex binders include STYRONAL 4681 available from BASF, Charlotte Steel Creek Road 11501, 28273, North Carolina, USA. Synthetic thickeners (or co-binders comprising carboxymethylcellulose (CMC) or acrylic acid-based or mixed based thickeners) are present at a concentration of at least about 0.05 parts by weight of the total amount of pigment. Suitable synthetic thickeners include STEROCOLL FD® available from BASF. Coating formulations are available from Minerals Technologies, Inc., 18017 Bethlehem Highland Avenue 9, PA, USA, and PCC or GCC, available from Omya, Proc. Main Street 61, 05765, Vermont, USA. It may also include.

Coating formulations can be prepared by mixing several components in one tank or pre-mixing and then combining the individual components. The mixture is generally shaken to homogenize the components. The resulting blend may have a viscosity of about 1000 to about 1500 cPs as measured by a Brookfield viscometer at 100 rpm. If this coating formulation is used, for example in a blade coater, its solids content may preferably be as high as about 53 to about 55% by weight, but plastic pigments are typically added to the formulation in the form of an aqueous dispersion having a low solids content. As such, the solids content of the coating formulation is more typically about 49 to about 51 weight percent. The sample coating formulation was 91% Contour 1500®, 5% RPS Vantage®, 4% Ropark H.P-1055®, 14 parts Styronal 4681®, And 0.7 parts of StyroCol FD®, having a 50% coating solids content and a Brookfield viscosity of 1000 cPs.

The coating formulation should be applied at a weight of about 2.0 to 6.0 pounds / 3300 square feet, preferably 2.5 to 5.5 pounds / 3300 square feet. Coating formulations are generally applied to both sides of the paper web, but this is not necessary. In general, coating formulations may be prepared from any conventional type of blade coater as specified in US Pat. Nos. 4,250,211 and 4,512,279, and / or fountains as specified in US Pat. No. 5,436,030, which is incorporated herein by reference. fountain type coaters and / or double blade coaters as specified in US Pat. No. 5,112,653. The coating formulation can also be applied using a metering size press, such as Metso's Optimizer. As used herein, a blade or blade coater is understood to include such other equivalent metering techniques, unless otherwise noted. The doctor blades described in US Pat. No. 4,780,336 have been advantageously used to provide lightweight coatings. Preferably, the coating formulation is applied using a blade coater to a substantially uniform thickness throughout the surface of the base paper. Preferably, the coating process is performed off-line or on-line. Prior to calendering, the coated web has a moisture content of greater than 5.5%, preferably greater than 6.5% and most preferably greater than 7.0%.

Wide-nip calendar

The coated paper is then subjected to two wide-nip calendars, preferably comprising a heated roll and soft shoe backing, as specified in US Pat. Nos. 6,332,953, 6,465,074 and 6,213,009, which are incorporated herein by reference. Calendaring can be done using a shoe nip calendar (SNC). In this type of calendar, a nip is formed between the cylindrical press roll and the arcuate pressure shoe. The latter has a cylindrically concave surface with a radius of curvature that is approximately equal to the radius of curvature of the cylindrical press roll. When the roll and shoe are in close physical proximity to each other, a nip is formed that can be 5-10 times longer in the machine direction than the nip formed between the press rolls. This increases the so-called dwell time of the cellulose fiber web in the long nip while maintaining the pressure per square inch of press pressure at an appropriate level. Using a schnip calendar maintains the original volume much more than a traditional supercalendar or hot soft calendar.

Coated paper passes through two calendering nips such that each side of the paper is treated with one of the calender nips opposite the heated roll, each calendering nip having a calender roll having a surface temperature of at least 300 ° F and a width of at least 30 mm. Formed by a backing shoe, the nip provides a load of at least 1000 pounds per linear inch; Calendered paper has a caliper retention of greater than 75%.

The resulting coated paper will generally have the following properties compared to conventional coated paper of the same weight:

(1) whiteness as high as 4.0% or less;

(2) higher opacity by 3.3% or less;

(3) calipers as high as 22% or less;

(4) paper gloss as low as 1-7%, but comparable or print gloss as high as 2-5%;

(5) a slightly rougher surface, 1.6 to 2.6 microns as measured by PPS at 10 kg clamping pressure (commercially acceptable PPS of 1.6 to 1.9 microns was achieved when using coatings A or B described below); And

(6) Lower weight per roll at the same roll diameter, demonstrating the higher bulkiness of the paper.

Paper

The following types of paper were used to examine the effect of five 32 g / m 2 papers: B1, B1 / hi-mechanical, B4 and two hot soft pre-calendered papers (B1). / Pre-calendering and B1 / high content-mechanical pulp / pre-calendering). The properties of B1 and B1 / high content-mechanical pulp stocks are listed in Table 1. Base B4 is similar to base B1 except that B4 adds less wet-end starch in the sheet. The pre-calendered base has a smoother surface than the pre-calendered base, but its caliper is reduced. Table 1 shows that as the TMP content increases from 30% to 60%, the total mechanical pulp content increases from 60% to 70%, while still maintaining good paper runnability. Table 2 shows that as the amount of mechanical pulp increased from 60% to 70%, the caliper increased from 2.85 to 3.03, while the toughness and porosity increased slightly.

Coating formulation

“Control” coatings include 79% standard delaminated kaolin having an average particle size of less than 2 microns and an average particle size of 0.75 microns when measured using a settling particle size analyzer; 7% calcined kaolin with a whiteness of 93%; TiO ₂ 7.5%; Hollow plastic pigment 6.5%; 8 parts starch; And 12 parts of styrene butadiene (SB) latex, a typical No. 5 lightweight coating having a 50.7% coating solids.

Coating Material A, 86% of fine plate-shaped kaolin having 90% of particles less than 2 microns and having an average particle size of 0.5 microns, measured using a sedimentation particle size analyzer; Hollow plastic pigment 5.5%; 14 parts of latex (SBAn) containing styrene butadiene and acrylonitrile monomers; And 0.25 part of a synthetic thickener, and has a solid content of 53.9%.

Coating Material B comprises 76% of a crude platy exfoliation kaolin having 60% of particles less than 2 microns and having an average particle size of 1.6 microns; 10% calcined kaolin with a whiteness of 93%; TiO ₂ 8.5%; Hollow plastic pigment 5.5%; 12 parts SBAn latex; And 0.25 part of a synthetic thickener, and has a solid content of 51.1%.

Coating Material C comprises 86% micromanipulated kaolin having 99% of particles less than 2 microns and having an average particle size of 0.21 microns; TiO ₂ 8.5%; Hollow plastic pigment 5.5%; 16 parts SBAn latex; And 0.25 part of a synthetic thickener, and has a solid content of 55.6%.

Coating process

Using a shortdwell blade coater, a coating as specified in Table 3 below was applied onto the base paper specified in Tables 1 and 2. The weight of the coating material was 5.7 g / m 2 at the wire side of the paper and 4.9 g / m 2 at the felt side of the paper. The wire side was coated first, followed by the felt side. All bases were coated at 2100 fpm except B4 base coated at 3700 fpm. The moisture content of the final coated sheet was adjusted to 5.5-6.0%.

The nature of the paper B1 standard B1 / High Content-Mechanical Pulp Furnish 40 kraft, 30 TMP, 30 GWD 30 craft, 60 TMP, 10 GWD` Other Furnish 18 Coated Broke 5 Returned Phage 5 coated phage, 5 returned phage Raw ash content (%) 5.7 3.1 Porosity (s) 21 23.7 Smoothness (SU) Top / Wire Side 235/292 245/299 formation 29.9 31.3 Opacity (%) 75.8 75.2

Comparison of the base Paper Caliper (mil) Gurley porosity (s) average / S.D. PPS 10 kg PPS 10 kg felt surface B1 2.85 20.2 / 3.1 8.11 6.26 B1 / Spare-Calendar ^* 2.19 25.8 / 2.6 4.89 3.84 B4 2.50 22.9 / 2.9 5.56 5.63 B1 / High Content-Mechanical Pulp 3.03 25.5 / 2.8 8.52 6.56 B1 / High content-mechanical pulp / preliminary calendar ^* 2.46 27 / 2.5 6.05 4.86 ^* 350 ℉ and from 15 psi each one side with the nip of the one hot soft pre-calendering was performed.

Coating formulation Control Coatings (Blades) A (blade) B (blade) C (blade) Standard peeling 79 Fine plate 86 Tempered plaque 76 Fine operation 86 Ansilex 93 7 10 TiO ₂ 7.5 8.5 8.5 8.5 Low Park 1055 6.5 5.5 5.5 5.5 SB Latex 12.5 SBAn Latex 14 12 16 Starch 8 Thickener 1 0.05 0.05 0.05 Thickener 2 0.2 0.2 0.2 Coating solids (%) 50.7 53.9 51.1 55.6

Calendering Process

The coated paper was calendered at 3000 fpm using an Optiwell well nip calendar manufactured by Metso Paper Inc. Using one nip per side, the calendering process was performed by first calendering the backside and then calendering the felt side. The heating roll temperature for the first nip was 350 ° F and the nip width was 70 mm, the second nip was 400 ° F and the nip width was 70 mm. The payload for the first and second nips was 2300 pli.

In addition, paper coated with a "control" coating was calendered using a conventional supercalender at 1000 fpm. The supercalendering roll temperature was 190 ° F. and the nip loading was adjusted to achieve 45% sheet gloss using a B1 blank sample. The same supercalendering conditions were used for B4 stock coated with a "control" coating.

Properties of Coated Paper

The properties of all coated sheets are specified in FIGS. Print performance was evaluated using a four-color web offset press at the Rochester Institute of technology (RIT), Rochester, NY. Also for comparison purposes, RIT printed several commercially available 30 pound products. The nature of typical 32-40 pound LWC paper or the industry average sample is also summarized and shown in the figures for comparison.

Caliper (FIG. 1)

Samples made of B1 and B4 paper, coated with a "control" coating and calendered on a supercalender, are calipers from 1.80 to 1.83 mil, identical to those of commercial products made from the same paper and coated with a "control" coating Indicated. The same sample calendered on the shoe nip calendar showed a much higher, about 22% improved caliper (2.18-2.20 mil). A 30 pound SNC coated sample made of B1 / high-mechanical pulp paper showed the highest caliper, caliper, which was the same or slightly better than that of a typical 40 pound LWC product. A 30 pound SNC coated sample made of pre-calendered paper had a lower caliper than its uncalendered counterpart, but was still within the range of a typical 36 to 38 pound LWC product. A 30 pound SNC coated sample made of B1 paper showed almost the same caliper as a typical 40 pound LWC sheet. A 30 pound SNC coated sample made of B4 paper showed a slightly lower caliper than that made of B1 paper but the same caliper as that of a typical 38 pound LWC sheet.

Compared to the samples coated with Coating A or Coating C, the samples coated with Coating B consisting of crude platy kaolin and calcined kaolin showed improved calipers. Overall, 30 pound SNC paper shows a much improved caliper, which is 17-27% higher than that of supercalendered counterparts (30 pounds), whether or not it is made of pre-calendered paper. It was. As indicated in FIG. 1, the main factor contributing to a much better caliper is the excellent bulk preservation of the shoe calender. Thus, increasing the initial bulk of the paper with the use of a shoe calender can achieve the highest final caliper.

In summary, FIG. 1 shows that a sample calendered using a shoe nip calendar and coated with a “control” coating exhibits a caliper about 22% higher than its supercalendered counterpart. Samples calendered using a shoe nip calendar and coated with coatings A, B, or C were about 12 to 22% more than the top-caliper commercial sheet (i.e. 30 # Mainebulk) used for comparison. High calipers (calipers from 2.12 to 2.32 mils). The effect of the coating formulation on the bulkiness was relatively small and only samples coated with Coating B showed slightly higher bulkiness. The effect of the base paper on bulkiness was expected much, that is, the pre-calendered paper showed lower calipers, and higher levels of mechanical pulp-containing paper showed higher bulk. Overall, B1 / high-mechanical pulp paper showed the highest bulk, followed by B1 paper, B4 paper, B1 / high-mechanical pulp / pre-calendering paper, and B1 / pre-calendering paper. It was.

Whiteness (Figure 2)

Uncalendered paper with a higher caliper showed higher whiteness than pre-calendered paper. Compared to the samples coated with the "control" coating, the samples finished in the SNC clearly showed higher whiteness than the supercalendar samples. This was due to the relatively low pressure and even less nip of the schnip calender. Samples coated with Coating A or Coating B had similar whiteness and were better than samples coated with Coating C. In general, the whiteness of the SNC samples was 72.7 to 74.5%, which was much better than commercial samples (30 pounds) as well as industrial samples (32 to 40 pounds).

In summary, FIG. 2 shows that shoe-calendered paper coated with a “control” coating exhibited about 1.1 to 3.0% higher whiteness than its supercalendered counterpart. Coating A was used in place of the “control” coating to achieve 0.2-0.6% higher whiteness. Samples coated with Coating B showed the same whiteness. Samples coated with coating material C exhibited a 0.3 to 0.5% lower whiteness. Increasing the amount of mechanical pulp in the paper decreased the whiteness. The base paper was pre-calendered and showed a whiteness comparable to or slightly higher than its pre-calendered counterpart. Overall, samples using B1, B1 / pre-calendering or B1 / high content-mechanical pulp / pre-calendering paper and coated with Coating A or Coating B showed excellent whiteness.

Opacity (Figure 3)

Similar to whiteness, opacity also varies greatly depending on the type of paper. Uncalendered paper (B1 and B4), specifically paper containing higher content of mechanical pulp, showed higher opacity. Samples coated with Coating A or Coating B (both consisting of tabular kaolin) had similar opacity, and both showed higher opacity than samples coated with Coating C or samples coated with "control" coating. Except for samples coated with Coating C and made of B4 paper, the opacity of the SNC sample was much better than commercial samples (30 pounds) and industrial samples (32-40 pounds).

In summary, FIG. 3 shows that shoe-calendered paper coated with a “control” coating showed about 2.0-2.5% higher opacity than its supercalendar counterpart. Coated paper (B1, B1 / pre-calendering, B1 / high content-mechanical pulp, and B1 / high content-mechanical pulp / pre-calendering base) was coated with Coating A or Coating B instead of the "control" coating. Furthermore, it exhibited about 1% higher opacity than the sample coated with Coating C, which exhibited about 1% lower opacity. The pre-calendered base showed 0.1-0.8% lower opacity than its non-calendar counterpart. Overall, samples coated with Coating A and made of B1 / high-mechanical pulp paper showed the highest opacity, followed by Coating A or Coating B and then B1, B1 / pre-calendering or B1 / high content- The samples were made from mechanical pulp / pre-calendering paper.

75 ° TAPPI sheet glossiness (FIG. 4)

Samples coated with a "control" coating finished at the SNC had a much lower gloss than those finished at the supercalendar. In fact, the SNC sample only had a gloss of 31 to 33%, which is much lower than the 30 pound commercial sample. In addition, the glossiness of the starch-containing control "coating material" was worse than the starch-free coatings A, B and C. The only sample that could reach 40% glossiness was the sample coated with Coating A or Coating C. In general, the smoother surface and lower porosity of the pre-calendered B4 paper provided improved sheet glossiness. Samples made from B4 paper and coated with Coating C had the highest glossiness (50%).

In summary, FIG. 4 shows that shoe-calendered paper coated with a “control” coating exhibited about 15-20% lower paper gloss than its supercalendered counterpart. Coating A was used instead of the "control" coating to achieve about 9 to 12% higher paper glossiness, and coating B was used to achieve about 2 to 5% higher paper glossiness. C was used to achieve about 12-17% higher paper glossiness. Pre-calendering was performed to achieve 2-5% higher sheet glossiness. Overall, paper coated with coating C had a higher gloss than coating coating A, and paper coated with coating B had the lowest paper gloss.

Surface smoothness measured by Parker Print Surf (FIG. 5)

Samples coated with a "control" coating and finished at the SNC had a worse Parker Print Surf (PPS) or rougher surface than finished at the supercalendar. PPS performance was not only dependent on the calendering method but also on the type of paper and coating material. For example, coarse paper such as B1 paper showed worse PPS than smoother paper such as B4 paper. For the same reason, pre-calendering, which improves the smoothness of the base paper, also improved the PPS compared to the uncalendered base paper. Coatings A and B consisting of plate-like kaolin showed better PPS than coating material C consisting of finely engineered kaolin. Thus, SNC samples showed worse PPS than commercial samples (30 pounds) as well as industry average samples (32-40 pounds).

In summary, FIG. 5 shows that shoe-calendered paper coated with a “control” coating exhibited a PPS about 0.1-0.9 points higher than its supercalendered counterpart. Coating A was used in place of the “control” coating, resulting in a decrease of about 0.1 to 0.6 points in PPS. Coating B was used and the PPS decreased by about 0.1 to 0.4 points. Coating C was used in place of the “control” coating, resulting in a 0.2-0.3 point increase in PPS. Pre-calendering reduced the PPS by 0.1 to 0.5 points. Overall, all papers coated with Coating A or Coating B exhibited a commercially acceptable PPS of 1.6 to 1.9 microns.

Print Glossiness (Fig. 6)

Print glossiness was measured on a four color black region, using a RIT web offset press print signature. Compared to samples coated with "control" coatings, it has been found that supercalendered samples have higher print gloss than SNC samples because they have higher sheet glossiness. Print glossiness, similar to sheet glossiness, also depends on the smoothness and porosity of the base paper, that is, the smoother surface and lower porosity of the pre-calendar B4 base paper provided improved print glossiness. Coatings A, B and C provided better print gloss than "control" coatings. In general, the SNC samples showed print gloss equal to or better than 30 pound commercial sheets. Of all SNC samples, samples made of B4 paper and coated with Coating A showed the highest print gloss.

In summary, shoe-calendered paper coated with a "control" coating showed about 7% lower print gloss than its supercalendar counterpart. Coating A was used instead of the "control" coating to achieve 10-12% higher print glossiness, and coating B was used to achieve 4-8% higher print gloss and coating C was used. This achieved 4-10% higher print glossiness. Pre-calendering resulted in 1-5% higher print glossiness. Overall, shoe-calendered paper coated with coatings A, B or C exhibited at least the same print glossiness as commercial sheets.

While the present invention has been described in terms of preferred embodiments, which are illustrative but not limiting, those of ordinary skill in the art will recognize that many modifications are possible in light of the above teachings. For example, different latexes and pigments can be used. All such variations and modifications fall within the scope and concept of the invention.

Claims (22)

(a) making a fiber furnish comprising mechanical pulp and chemical pulp; (b) forming a paper web from the fiber furnish; (c) removing water from the web; (d) applying a coating having a weight of at least 2.0 pounds / 3300 square feet per side on each surface of the web to form a coated web having a moisture content of greater than 5.5% and a caliper greater than 2.6 mil; (e) passing the coated web through two extended-nip calenders so that each side of the paper is treated with one of the calender nips opposite the heated roll (each calendering nip is at least 300 ° F.) Formed by a calender roll having a surface temperature and a backing shoe having a width of at least 30 mm, the nip provides a payload of at least 1000 pounds / linear pli, whereby the calendered paper is greater than 75%. And a caliper preservation rate). The method of claim 1 wherein the paper is No. 5 offset lightweight coated paper. The method of claim 1 wherein the furnish comprises at least 40% mechanical pulp. 4. The method of claim 3, wherein the furnish comprises about 60-80% mechanical pulp. The method of claim 1 wherein the coating has a weight of 2.0 to 6.0 pounds / 3300 square feet per side. The method of claim 1 wherein the coated web has a moisture content of greater than 6.5%. The method of claim 1 wherein the coated web has a moisture content of greater than 7.0%. The method of claim 1, wherein the coating material is a hollow plastic pigment; Kaolin pigments; Calcined kaolin clay; Titanium dioxide pigments; Synthetic latex binders; And a co-binder comprising a synthetic thickener, or a thickener based on carboxymethylcellulose or acrylic acid-based or a mixture thereof. 9. The method of claim 8, wherein the coating material also comprises hard calcium carbonate or heavy calcium carbonate. The method of claim 8, wherein the hollow plastic pigment is present in an amount of at least about 2% by weight of the total amount of the pigment. The method of claim 8, wherein the hollow plastic pigment is present in an amount of about 3 to 5 weight percent of the total amount of the pigment. 9. The method of claim 8, wherein said kaolin pigment has at least 85% of the particles of less than 2 microns and at least 50% of the particles of less than 0.5 microns when counting the particles using a settling particle size analyzer. . 9. A method according to claim 8, wherein said kaolin pigments are fine coarse particles having more than 15 form factors. 9. The method of claim 8, wherein said kaolin pigment is a fine coarse particle having a form factor of about 20 to 27. 9. The method of claim 8, wherein said kaolin pigment is present in an amount of at least 70% by weight of the total amount of pigment. 9. The method of claim 8, wherein said kaolin pigment is present in an amount of from 80 to 100% by weight of the total amount of pigment. The method of claim 8, wherein said titanium dioxide is present in an amount of at least about 2%. 12. The method of claim 11, wherein said titanium dioxide is present in an amount of about 3 to 5%. The method of claim 1, wherein the coating material is applied using a blade coater or a metering size press. The method of claim 1, wherein the calendar is a shoe nip calendar, the shoe nip is about 40 to about 80 mm wide, the calendaring temperature is at least 300 ° F., and the nip load is 1700 to 2400 pli. The method of claim 1 wherein the calendered paper has a basis weight of 28 to 38 pounds / 3300 square feet, exhibits a 75 ° TAPPI glossiness of at least 35%, and exhibits a caliper of at least 2.15 mils. (a) making a fiber furnish comprising at least 40% mechanical pulp; (b) forming a paper web from the fiber furnish; (c) removing water from the web; (d) applying a coating on each surface of the web with a coating weight of at least 2.0 pounds / 3300 square feet per side using a blade coater to form a coated web having a moisture content of at least 5.5%; (e) passing the coated web through two wide-nip calenders so that each side of the paper is treated with one of the calender nips opposite the heated rolls (each calendering nip has a calender having a surface temperature of at least 300 ° F.) Formed by a roll and a backing shoe nip having a width of at least 30 mm, the nip provides a load of at least 1000 pounds / linear pli, whereby calendered paper has a caliper retention of greater than 75%). , (I) a hollow plastic pigment in which the coating material is present in an amount of at least about 2% by weight of the total amount of the pigment; (ii) a kaolin pigment present in an amount of at least about 70% by weight of the total amount of the pigment, wherein the kaolin pigment has a fine particle size distribution characterized in that at least 85% of the particles are less than 2 microns and at least 50% of the particles are less than 0.5 microns Having a plate-like shape, characterized in that it is a fine coarse particle having a shape factor of more than 15, preferably 20 to 27); (iii) titanium dioxide present in an amount of at least about 2% by weight of the total amount of the pigment; (iv) calcined kaolin present in an amount of at least 5% by weight of the total amount of the pigment; (v) synthetic latex present at a concentration of at least about 12 parts by weight of the total amount of pigment; And (vi) synthetic thickeners present at a concentration of at least about 0.05 part by weight of the total amount of pigment, Finished coated paper has a basis weight of 28 to 38 pounds / 33 square feet, exhibits 75 ° TAPPI glossiness of 35% or more, has a caliper of 2.15 mils or more, compared to a 30 lb / 3300 square feet LWC supercalendered Providing calipers as high as 17 to 27%, having improved bulk properties by up to 22%, and having improved whiteness, opacity and print glossiness, Method for producing ultra-bulk offset lightweight coated paper.