JP2646428B2 - Papermaking method - Google Patents

Description

The present invention relates to a papermaking method and apparatus, and more particularly, to a method and apparatus for producing relatively high density, high quality paper.

[Problems to be solved by conventional technology and invention]

Generally, paper production involves flowing a dilute aqueous suspension of wood pulp fibers over a running coarse wire screen from which most of the liquid is passed. It is also known to flow a dilute aqueous suspension of wood pulp fibers between two such screens. Further, moisture is often removed by processing steps such as applying vacuum and / or pressure. That is, a method of passing a wet web through a nip formed by opposed rolls, that is, a wet press method may be used. It is also known to further reduce the moisture content by passing the paper web over a rotating superheated cylinder, in which case,
Evaporation can reduce the water content to less than 15%.

In papermaking processes, it is often desirable or necessary to improve certain properties of the paper web. That is, a problem recently encountered in the art is the need for higher quality paper with the introduction of high speed printing.
In particular, paper having both a higher density and a relatively low moisture content is a prerequisite for certain printings. For example, when performing multi-color printing on a sheet, following the application of the first color, the printed sheet is passed through a drying step, and subsequently the next color is applied. If the moisture of the sheet entering the drying process is too high (eg, greater than 8%), the sheet will shrink during the drying process and will not be in a state suitable for applying the next color.

In other words, for certain printing needs, it is desirable to provide a paper web having a high density and low moisture content. Increasing the moisture during machine calendering to achieve higher densities without grinding the paper web,
It has been proposed to facilitate the densification process. However, this results in the above blackening / mottle dyeing, which works against the purpose of obtaining a low moisture content. In order to achieve the desired result, multiple highly organized steps must be used and relatively expensive processes must be operated.

It is an object of the present invention to provide a method and apparatus for producing a paper web having a relatively high density and low moisture and suitable for multicolor printing.

[Means for solving the problem]

The present invention proposes an improved method of producing high quality paper suitable for multicolor printing, comprising the steps of preparing a pulp furnish of fibers, forming a wet web from the stock. Removing water from the wet paper web to reduce its moisture content from about 55% to about 15%, as needed, super / soft calendering the web to substantially increase the web density; Treating the web to reduce its moisture content.

Also provided is an improvement in papermaking equipment, the apparatus comprising means for preparing pulp stock of fibers, means for forming web web from stock, means for removing moisture from web web to a level of about 55% to about 15%. And the improvement comprises means for supercalendering the paper web to substantially increase the web density while the paper web has a moisture content between about 55% and about 15%. This is an improved device.

As mentioned above, it is often desirable to improve certain properties of the paper web in the papermaking process, and therefore, the calendering operation of passing the paper web through a sequential nip formed between heavy rotating rolls in a calendar stack into the paper nip. Often multiply. In this regard, the dried paper web may be subjected to either a "hard" calendering process or a "super" calendering process. The hard calendaring process operation consists of passing the paper web between a pair of rolls, each surface formed of a rigid inelastic material. On the other hand, super-calendering (sometimes called soft-calendering)
This is done between a pair of rolls where the surface of one roll is made of a rigid inelastic material, while the surface of the opposing roll is made of a rigid elastic material. These calendering operations can be performed in-line with the other steps of the papermaking process, ie, web forming, pressing and drying, and are therefore referred to as on-machine calendering. If calendaring is not performed inline, it is referred to as off-machine calendaring. In current papermaking technology, supercalendering is usually performed off-machine.

Other calendaring and / or wet pressing operations or similar types of operations are also known. That is, in situations where a wire or dandy roll or press felt leaves a mark on the wet web,
It may be desirable to remove these marks while the web is highly plastic. In such cases, a smoothing press is used just before the drying section. This smoothing press
Plain except where no felt is used
It is composed of two rolls similar to a press roll,
This wet web is pressed very lightly between two very hard surfaces. These surfaces are made of metal or granite (granite) materials, sometimes using extremely hard rubber materials. More recently, calendering operations have been used within the dryer section itself, especially for groundwood. The point at which calendering is performed depends on the desired paper characteristics. This operation is called breaker (stack) calendaring. This breaker calendering operation is performed utilizing substantially the same equipment used for machine calendering (ie, hard calendering where the surfaces of the nip rolls are both made of a rigid inelastic material). The main function of breaker calendering is to smooth the sheet and flatten all high points, but to avoid damaging the sheet, mottled dyeing or blackening as the moisture content may be high and the web may be weak Low nip pressure must be used.

As is clear from the above, hard calendaring is
It can be used both in the dryer section and in a step following the drying step. In general, breaker calendering utilizes only very low nip pressures, whereas machine calendering (hard calendering) is utilized with less than 15% moisture and low to high nip pressures. On the other hand, supercalendering is generally only used in the low moisture range, usually only off-machine. Other types of calendering, such as gross calendering or similar, where there is no substantial reduction in thickness / calipers or substantial increase in density (eg, due to various issues such as "shiny" / mottled surfaces) The "finishing" operation also uses soft calendering techniques at less than 15% moisture. Industrial applications usually involve paperboard grades. This is known, for example, from US Pat. No. 3,124,504. This patent teaches the use of a nip that includes a hard metal surface and a hard elastic surface to impart some surface properties to the uncoated web. There is no teaching in them that it is desirable to achieve a substantial reduction in thickness or consequently an increase in web density, the object of the present invention. On the other hand, the inventor achieves a substantial reduction. For gross or similar calendering operations, 5-
A reduction in thickness (or increase in density) of more than 10% is considered to be a substantial reduction (or increase) depending on the grade of paper or paperboard.

Further, Mahoney et al. Did not provide data in support of their method, and findings indicate that there is no industrial success with this method. Lack of this industrial success is Miherich
lich) by his U.S. Pat. No. 3,759,785, in which his soft-calendering method can only be applied to uncoated paper (newsprint) in the moisture range of 12-15%. (Column 8 23
~ 25 lines).

In view of the above, the term "compacting / calendering / soft calendering / calendar" as used herein by the inventor is therefore intended to refer to a press operation / calendering operation (which is a wet press operation / wet press, smoothing / Smoothing press / calender, finishing / gloss rendering / gloss calender).

The present invention utilizes a web web, as described above, preferably having a moisture content of about 55% to about 15%. This wet paper web can be supplied by conventional means.
That is, in a normal papermaking operation, a dilute aqueous suspension of pulp fibers can be run over a running coarse wire screen to remove a substantial portion of the water through the screen. In addition, the moisture can be removed by conventional processes, such as by applying a vacuum or using a press roll or other process, to partially dry the web to the desired moisture content. If desired, the web can be further processed to increase its integrity.

The web is subjected to an on-machine supercalendering operation while at a moisture content between about 55% and about 15%. That is, the paper web is passed between a pair of rolls, one of which is made of a rigid inelastic material, such as a metallic material, and the opposing roll is made of a rigid elastic material, at the desired moisture content. Materials capable of forming rolls are known, and the terms "soft" and / or "super" calendaring are well known to those skilled in the art, but more specific aspects are described below.

As noted above, calendaring involves many variables / parameters, many of which interact in a highly complex manner, which is well documented. However, one parameter is of interest here, namely the hardness and properties of the material forming the elastic roll surface. Usually "cotton filled"("co
Some materials are referred to as "ton filled"), and other materials are referred to as "elastmeric". Special elastomeric materials or calender rolls which have been found to be useful in the present invention are those manufactured by Edouard kusters (West Germany) and sold by the company under the trade name "MAT-ON-LINE". It is.

As mentioned above, the paper web can be subjected to a supercalendering process while having a moisture content of about 55% to about 15%. The present inventor has found that the present invention is effective in the moisture range of about 55% to about 15%, but the lower limit of the moisture is just above the prior art itself without causing blackening of the sheet. This is the limit found to be unable to be implemented effectively. On the other hand, it was found that the upper limit of the moisture was such that the moisture could not be extracted any more by the ordinary wet pressing operation. Furthermore, depending on the compacting / drying steps performed earlier, it may be necessary to improve the integrity of the web /
The strength was found to be that which was sufficient to withstand the soft calendaring operation / process. This moisture level has also been found to vary widely depending on the nature of the web stock. At these high moisture levels, the adhesion of the web to the roll can be severe, but to counter this, the release agent / surface can be used effectively, otherwise it is also The upper limit can be determined.

However, supercalendering is preferably performed when the moisture content of the paper web is between about 20% and about 45%. However, the optimum specific moisture content for any particular paper web will depend on many variables or parameters. That is, factors such as machine speed, nip pressure load, roll diameter, number of nips through which the web passes, calendering temperature, type of stock used for the web itself, surface properties and hardness of the elastic roll, etc., must be taken into account. Must.

The temperature of the web entering the nip will also depend on other factors. In other words, it is possible to increase the moisture and temperature of the web to near the boiling point of water by using a steam shower, and to change the steam in various places by using a partitioned steam box to make the super It is possible to control the nip pressure distribution of the calendering operation. However, one limiting factor for the calendering temperature will be the type of material utilized to form a solid elastic roll surface for the supercalendering process. If an elastomeric material is used, too high a temperature will adversely affect the roll surface / bond between the elastomer and the metal core. If the temperature is too high, the sheet tends to dry out during processing. Nevertheless, by controlling both the web temperature and the temperature of the surface of each pair of rolls, the inventors have found that the overall soft calendering temperature can be controlled. That is, within the temperature limits of the elastic roll surface, the inventor can reduce the nip pressure intensity / charge for a given compaction effect by using a higher calendering temperature, or vice versa. The present inventor has found in the direction of interest of higher quality sheets that a greater compaction can be obtained for a given nip charge.

Another embodiment which the inventors have found advantageous is to divide the soft-calendering operation at high moisture into two or more steps, with or without intermediate drying. For example, a light soft calendering stage in the 45-55% moisture range (where the density is 10-20%
Increased), followed by drying the web to a range of 25-35%, and a heavier soft calendering step / process (where the density is further increased). In this embodiment, good effects can be obtained using infrared drying, but it is possible to use a drying technique in which the web is dried under pressure, such as a combination of a dryer felt and a cylinder. preferable. An embodiment including a combination of the inventor's novel soft calendering process and other prior art calendering processes is shown below with accompanying data.

〔Example〕

In a first test embodiment, an industrially produced newsprint web was subjected to supercalendering on a pilot plant machine. The web had an initial moisture content of 9%, and the paper web was passed multiple times between nips having various nip pressures as shown in Table 1 and plotted in FIG. 1 (curve A). The following various properties were tested on the stock of this paper web.

Subsequently, a web of newsprint was removed from the industrial paper machine at the breaker stack at about 31% moisture. By the time the web was ready for further processing on pilot plant machines, the moisture had dropped to the range of 25-30%. This wet paper web was then subjected to a soft calendering process similar to the previous embodiment. The parameters and results are shown in Table 2 below and plotted in FIG. 1 (curve B).

In the next test embodiment, the wet paper web was again removed from the industrial paper machine at the breaker stack location with the same moisture content as the stock in Table 2. The stock was subjected to a soft calendering operation at a moisture content of 22-23% to dry to about 9-10% moisture and then further soft calendered. The results are shown in Table 3 below and plotted in FIG.

In addition, another test embodiment was performed as in Examples 2 and 3, again utilizing the newsprint web from the breaker stack location of the industrial paper machine. In this embodiment, the paper web was subjected to initial soft calendering at a moisture content of 22-23%, dried to about 9-10%, and then subjected to final hard calendering at reduced moisture levels. The results are shown in Table 4 below and plotted in FIG.

Referring to FIG. 1, curve A shows that the web has a low moisture content,
That is, it shows how the web density increases when subjected to conventional off-machine supercalendering at about 9%. Curve B, on the other hand, shows the increasing density of the web as it was subjected to the method of the present invention, ie, on-machine soft calendering at a higher moisture content (25-30%). Curve A and Curve B
It is clear that practicing the present invention makes it easier to obtain higher density webs with the same "cumulative nip pressure".

That is, referring back to Table 1 above (curve A), the density of Sample 11 represents a "standard newspaper" sheet and is achieved in Samples 5-9 in Table 2. It does not represent the density of higher quality gravure sheets.

FIG. 2 and Table 3 show that a breaker stack supercalendering and air-drying step followed by practicing the present invention in combination with supercalendering can provide gravure grade excellent quality sheets. This is an example. In this method,
Density increased by about 80%.

FIG. 3 and Table 4 illustrate that the combination of supercalendering at high moisture, air drying and then hard calendering with several light nips can yield good quality gravure sheets. I have. The use of supercalendering, generally at higher moisture, substantially reduces the number of nips / nip pressure required for final calendering of the sheet. This is very useful because calendering, especially hard calendering, can be damaging and expensive.

Referring again to Tables 3 and 4, by applying an ink film to the sample using a special drawing rod, supercalendering versus hard calendaring (both low moisture) after soft calendaring at higher moisture. Comparing the results, the hard calendering still had a greater mottle tendency than the soft calendering, which did not show any mottle tendency. Thus, the prior art methods, while capable of producing high density paper, are mottled or "galvanized" (galvanizin).
g) still plagued these attempts. The present invention has apparently eliminated this mottled effect, which made high quality printing extremely difficult, if not impossible. In addition, the density distribution is more uniform and the surface is more "flat".

Equipment for soft-calendering is well known,
Examples of suitable devices include U.S. Patent Nos. 3,365,774 and 4,256,034 (Kusters) and 3,124,504 (Mah
oney etc.). The above examples deal with newsprint grade paper, but if higher density is required with satisfactory printing characteristics, other grades of paper and paperboard, including a wide range of calipers or thickness ranges Can be used as well.

As is evident from the above, in practicing the present invention, a substantial increase in density is achieved using a super / soft calendaring operation. The web "remembered" the calendering operation before it was applied, and it was found that what was most important was the total nip pressure applied to the web throughout the super / soft calendaring. It will also be apparent that other changes and modifications can be made to the specific embodiments described above without departing from the spirit and scope of the invention.

[Brief description of the drawings]

FIG. 1 is a graph showing the correlation between the cumulative applied nip pressure and the sheet density in Tables 1 and 2. FIG. 2 is a graph showing the correlation between the cumulative applied nip pressure and the sheet density in Table 3. FIG. 3 is a graph showing the correlation between the cumulative applied nip pressure and the sheet density in Table 4.

Claims (8)

(57) [Claims] 1. A papermaking method comprising the steps of: (1) adjusting fiber pulp stock; (2) forming a wet paper web from the stock; (3) ) Removing moisture from the wet paper web to reduce its moisture content to about 55-15%, and (4) soft calendering the web without causing blackening / dappled paper web. By applying pressure and heat to increase the paper density by at least 10% while maintaining the moisture content of about 55-15%, and subsequently treating the web to further reduce its moisture content The process of producing high-quality paper suitable for multicolor printing. 2. The method of claim 1 wherein the step of further treating the web comprises the step of drying the wet paper web and subsequently further calendering the web. 3. The step of further calendering the web,
3. A method according to claim 2 including the step of supercalendering the paper web following drying. 4. The method of claim 2 wherein the step of further calendering the paper web includes the step of hard-calendering the paper web. 5. The method of claim 2, wherein the step of further calendering the paper web comprises the step of soft calendering the web at a moisture of less than about 15%. 6. The method of claim 2 wherein the step of soft calendering the paper web comprises the step of soft calendering the web while at about 20 to about 40% moisture. 7. The method of claim 1 wherein the web density is reduced from soft calendering.
2. The method of claim 1 wherein said method increases by 10 to about 80%. 8. Forming a pulp stock of fibers into a web web;
And a papermaking method for reducing the moisture content of the web, wherein the web has a moisture content of about 40 to about 20%.
The method of claim 1 wherein the steps of soft calendering the web to substantially increase the density of the web and subsequently drying the web to obtain a finished paper are improvements.