JPS5916039B2 - External sizing of extensible paper - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides fundamentally improved stiffness, tensile properties, TEA
EXTERNAL SIZE FOR IMPROVING PROPERTIES AND RUPTURE CHARACTERISTICS TO PAPER 9 A method and apparatus for producing zinc densified paper.

Stretchable paper (densified paper) made by the apparatus and method described, for example, in US Pat. No. 2,624,245, has certain well-recognized advantages and industrial applications. Such paper is subjected to compression densification in the direction of web travel (machine direction or MD) between pressure nips in a partially moistened state, thus densifying and forcing the fibers together. Provides inherent extensibility without crepe formation. Densified paper has improved tensile energy absorption (TEA), burst and tear properties that are highly desirable for applications such as paper bag manufacturing. However, extensible paper has reduced tensile strength and stiffness, and this reduced property makes it difficult to make the paper into bags. 5. The object of the present invention is to improve the tensile strength and stiffness of densified papers without compromising the tear strength, and also to produce fundamental improvements in TEA and burst strength.

The way to achieve these objectives consists in selective impregnation with starch as external sizing, especially without destroying the extensibility of the paper. External sizing of non-stretch papers is well known and commonly used to improve the print quality of premium papers by applying a coating of clay, polyvinyl alcohol, etc. to one or both sides.

``On Machine Surf Ace Sizing Trials with Acid Modified Wheat.''
An article entitled "Fura-ichi" in Tatsupi Volume 53, No. 8 (August 1970 issue) states that kraft paper can be made by adding acid-modified wheat flour or hypochlorite oxidized starch to kraft paper. The sizing had the effect of increasing burst strength and tensile strength. U.S. Pat. No. 3,362,869 describes applying a starch coating to one side of wet compacted paper before drying the paper to provide a gloss. According to the teachings of this patent, conventional polishing of densified paper by reintroducing sufficient moisture into the web for glazing after densification greatly destroys the extensibility of the web and its attendant benefits. There are times when it happens. Therefore, in order to avoid undesirable wetting of the web, a starch coating is applied to one side of the web which densifies the web and is still wet immediately before entering the drying roll, thus preventing an increase in the moisture content of the web. On the one hand, the starch adhesively bonds the web to the drying roll, causing a glaze on the starch-coated side of the web when the web is held under pressure against the roll. It is an object of the present invention to treat a densified paper web with a starch solution in a special way that overcomes or does not pose problems on the densified web caused by the introduction of moisture into the web. be.

According to the present invention, the controlled application of a starch-containing aqueous solution on both sides of a densified paper web under optimal conditions increases the tensile strength of the web up to 150% and the burst strength up to 400%.
It was found that tensile energy absorption (TEA) increases by up to 300% and stiffness increases by up to 100%. As a result of these wonderful and surprising improvements, it is now possible to utilize some pulp stocks that were previously thought to be completely unsuitable for the manufacture of paper bags, and which would otherwise be too strong. This makes it possible to reduce the amount of conventional raw material pulp stock used.
Another object of the invention is to provide a method for externally sizing a densified paper web, the method comprising:
The moisture absorbed into the web is adjusted so that after drying the web retains essentially all of the improved qualities imparted by densification and further improves its tensile, burst, TEA and stiffness properties. Meanwhile, apply 1 to 10% starch solution, such as potato, corn or wheat starch, to both sides of the web under pressure. It consists of impregnation.

The stiffness imparted by such processing makes densified paper almost as stiff as non-densified paper (enabling such paper to be easily converted into bags), while possessing many other strength qualities. is greatly improved when compared to densified and, of course, non-densified papers. The present invention includes that internal resin sizing may be used to control moisture absorption during application of the starch solution to the web.

Other methods for selectively controlling moisture absorption may also be used, for example, the strength of the starch solution is adjusted according to the elapsed time between application of the starch solution to the web and subsequent drying of the web. be able to. In another application of the principles described above, relatively unrefined paper fibers may be treated by the method of the present invention to produce paper products having values at or near the best tensile and tear strengths. It is possible to make it.

The unrefined paper fibers in the web exhibit relatively higher tear strength and lower tensile strength than webs made from refiner-treated fibers. The impregnation of starch sizing shown herein can provide a corresponding increase in tensile strength over unrefined fibrous webs without substantial loss of substantial tear strength. Other objects of the invention will become apparent from the following detailed description, including the following examples and the accompanying drawings.

Referring to the drawings, FIG. 1 generally depicts a densifier 10 for producing a uncreped extensible paper web 11. As shown in FIG. The densifier 10 includes a looped elastic running belt 12 and a rotating cylinder 13 having a smooth (chromed) outer surface for receiving the web 11. A number of guide rolls 14, 15, 16 and 17 are located within the loop of the belt 12, and the guide roll 14 operates to squeeze the belt 12 against the cylinder 13 at the press nip N.
Belt 12 temporarily decreases in thickness as it travels between nips N. The area of the guide roll 15 is located at a distance from the first guide roll 14, and on the open exit side of the nip N, the section 12a of the belt is forced against the cylinder 13, and the web guiding devices 18, 19 move through the nip N. The web is fed onto the cylinder 13 for movement through. A densifier 10 is shown located in the paper machine between the second and third dryer sections. The dryer roll shown partially cut away at 20 represents the last roll of the second drying zone, and roll 33 (also shown partially cut away) represents the tenth roll of the third drying zone 30. show.

The web passes from the dryer roll 20 under the paper roll 19 and over the expansion (paper guide) roll 18 and then into the nip N. Before entering the nip N, the web 11 is brought into contact with the chromed surface of the roll 13. The web 11 is then held against the plane of the roll 13 for a suitable angular distance by the belt section 12a, and then the belt 12
and paper guide roll 2.
2 and another expansion guide roll 23 onto a dryer roll 33. The web 11 exiting the dryer drum 20 has the optimum amount of moisture required for the densification process.

This optimum amount is 20 to 5 when the web 11 enters the device 10.
It can be varied at 0% by weight. Outside the above moisture content limits,
In other words, even if it is less than 20% by weight, is it still 50% by weight? Even if the paper exceeds 100%, it is not possible to perform the densification process to make stretchable paper. As mentioned above, the roll 13 has a smooth surface, for example a chrome plated surface.

Roll 13 is mounted on bearings 13a for rotation and is driven by a suitable power source such as a motor, generally designated M. In fact, the motor M is the driving force for the entire device 10. In this manner, the roll 13 drives the belt 12 by pressing against it primarily at the nip N, thus causing the tension in the belt 12 to drop at the nip N. As can be seen, each guide roll e.g. roll 14
, 15, 16 and 17, and the point at which belt 12 is driven (in this case nip N) is the point at which the tension in the belt decreases. be. Due to the elastic nature of the belt, there is a slight reduction in the stretching of the belt, which results in a drop in tension. is compressed into a web 11. The smooth surface of roll 13 contributes to the opposing slip between web 11 and roll 13. The web 11, which is held in close frictional contact with the belt, is densified in the machine direction (MD) without creping. Apply lubricant shower 1 25 to web 1 on the entrance side of nip N.
Provided directly under 1. The lubricant shower 25 is preferably a silicone shower, but other mold release agents are also suitable, which apply a relatively small amount of liquid in the form of a film to the surface of the roll 13. Roll 13 is heated as shown by steam S fed coaxially into roll 13 in the manner of feeding steam into a conventional paper dryer drum.

The steam is applied to the roll 13 so as to create a very thin steam film or cushion between the web 11 and the drum 13.
Maintain a relatively high temperature of about 212-350F.
This steam cushion helps to allow relative slippage between the web 11 and the drum 13 (this is an essential requirement for densification of the web by means of a belt), and helps to allow some of the certain components of the paper to evaporate. It has a tendency to cause softening. The apparatus described above is well known and does not form part of the present invention other than to indicate the subsequent processing according to the invention, the production of densified paper.

The following discussion herein will be directed exclusively to the treatment of densified paper in accordance with the teachings and findings presented by the present invention. As shown in FIG. 2, after leaving the densification machine 10, the web 11
passes through a dryer section 30 which includes conventional drying rolls 31-36.

The web 11 first passes over dryer rolls 33 and from there advances to rolls 34, etc. as shown. Felt dryer belts 37 and 38 are disposed on guide rolls 39 and contact each dryer roll 31-36 to ensure a tight engagement between web 11 and each dryer roll. The moisture content before entering the densifier 10 is 20-50% by weight. After the web leaves the densifier 10, the moisture content in the web is about 35-45% by weight. This needs to be increased or decreased to bring the web to the optimum moisture content for best densification. This includes the type of paper pulp used to form the web, the length of the fibers, the mixing state of fillers contained in the pulp, the properties of the web, such as the weight,
Select as appropriate depending on effectiveness, strength, etc. Dryer area 30
After passing through the web 11, the moisture content of the web 11 is about 1 to 15% by weight. Note that, as will be described later with reference to FIG. 3, the web 11 may be directly supplied to the size press described below without using the dryer. At this time, the water content can be up to 40%. It has been found that with such moisture content the subsequent starch impregnation can be carried out conveniently. Reference number 40
1 shows a size press arrangement for processing a dry densified web 11 according to the invention. The web 11 first passes over guide rolls 41, 42 and thence into a nip formed by two counter-rotating size press rolls 43 and 44. Nozzles 46, 47 adjust starch metering valves 48, 49 in conduits 50, 51 so that a fixed amount of starch solution 52 flows into the nip between size presses 43, 44. Helicopter collection discs 53 collect excess starch solution at each end of the nip. The starch solution is supplied from a starch solution supply tank 54 having an agitator 56 therein, and the starch in solution form is pumped from the tank 54 via a conduit 57 to a pump 58.
, where it is fed to metering valves 48 and 49. The starch return pump 60 is connected to the line 61 from the collection board 53.
The starch solution is returned to supply tank 54 via line 62. During the passage of web 11 between the nip of press rolls 43 and 44, a starch solution is applied under pressure to both sides of the web in varying percentages as shown in the examples below.

Starch solution and web 11 passing between rolls 43, 44
The passages are sufficient to cause starch impregnation on both sides of the web 11 in a predetermined amount and allow adjustment as to the concentration and rate of application of the starch solution. The amount of starch impregnated and deposited into the web should be between 1 and 10% by weight relative to the total weight of the web after drying to achieve good results? The best values for various density characteristics are as follows.
Obtained by impregnating with starch according to the percentages shown in Figure 9. During this process, the moisture content of the web changes from 1-15% by weight at the exit of the drying zone 30 to 35-45% by weight. rise to Less than 35% by weight is necessary to properly permeate the starch solution into the web, and 45% by weight? If this is exceeded, the extensible paper will become weak and tearable, making it difficult to dry in the subsequent process.

After applying and impregnating both sides of the web 11 with starch,
The web 11 passes around guide rolls 64 and into a fourth dryer section 66. Dryer section 66 contains a number of dryer rollers 67, 68, 69, 70, etc. around which dryer felts 71, 72 guided by rolls 73 pass. The dryer section 66 is similar in all respects to the dryer section 30 in that the web 11 passing therethrough loses the water imparted by the size press 2 to a moisture content of about 5 to 10% by weight of a typical paper web. %. FIG. 3 shows another embodiment of the invention, in which the same parts as shown in FIG. 2 have been given the same reference numerals.

According to the embodiment of FIG. 3, the web 11 proceeds directly from the densifier 10 without first entering the dryer section 30. As a result, the web 11 weighs approximately 30 to 40 kg before passing between the size press rolls 43 and 44.
contains water. Since the web 11 contains such an amount of water, it is conceivable that a smaller amount of starch solution will impregnate the web, however, giving superior advantageous results in terms of improving tensile, bursting and TEA properties. A sufficient amount of starch impregnates the web. The improvement achieved with the arrangement shown in FIG. 2 can be expected to be on the order of 50%. After passing through the size press 40, the web 11 is fed into a dryer section 66 where the moisture content of the web is between 5 and 10% by weight of a typical paper web. decreases to Third
An advantage of the arrangement shown is that one dryer section is used to receive the web from the size press. However, the moisture content of the web requires a large dryer area to reduce the moisture content to an acceptable degree.
For both the arrangements of FIGS. 2 and 3, if the starch solution provides sufficient bonding of the web to the cylinder when applied at the press 40, the web can be placed downstream of the size press 40 around a single dryer roll. It should be noted that it is possible to obtain a glaze of the paper web 11 by feeding.

For ejection, the pressure roll is
Contact with a drying cylinder as shown in US Pat. No. 2,869. The difference between the press arrangement and the arrangement of U.S. Pat. No. 3,362,869 is that in the above patent the starch applied is a surface coating to achieve an adhesive bond between the web and the dryer roll, whereas in the present invention the starch applied is a surface coating to achieve an adhesive bond between the web and the dryer roll. is tensile,
In order to achieve additional improvements in bursting and TEA strength, the aim is to impregnate the web with starch on both sides.
This additional effect is made possible by the use of a size press that includes size press rolls to force the starch solution into both web surfaces. Having described the apparatus of the invention, several examples are provided below to illustrate the individual components used in practicing the invention. Example
1 Raw materials: 30% unbleached softwood 70% unbleached hardwood No treatment: (Williams Freeness test 12 seconds) Example 3 Raw materials: 30% unbleached softwood 70% unbleached hardwood No treatment: (Williams Freeness Test 40 seconds) Starch: (Acid-modified corn starch) From the above examples, it is clear that two factors strongly influence the results.

These are (1) the degree of treatment of the refiner used and (2) the type or amount of starch added. Corn starch promotes greater improvements in tensile strength and stiffness than potato starch under the same conditions. These properties were desirable to be improved to even better properties. Furthermore, the tear strength for densified paper increases with refiner treatment,
Increasing the amount of starch added generally decreases the freeness level that occurs during normal bag manufacturing.
The effect on sizing is not large enough to offset the other benefits of sizing. Generally, when potato starch is added at 3-4%, the properties average out and do not show significant changes beyond this addition level. In contrast, when corn starch is added, the properties tend to continue to slope beyond this point. No stickiness or brittleness was observed in any of the samples tested up to about 8%. However, above this level, some brittleness was observed. While maintaining the principles of the invention, we have shown that slightly modified (plasticized) starch is superior to highly modified starch, especially at high levels of starch loading.

Such plasticized starch should be highly densified with the extensibility of the densified paper. However, since the examples presented herein use starch in a highly processed form, there is no indication that the use of unmodified starch is undesirable. Referring to FIG. 4, a decrease in tear strength occurs with increasing starch content at 525 CF (Shopper Grain 23.7) for the densified paper.

This experiment was conducted using acid-modified corn starch (Eclipse N) made by E.I. Starley. Refiner with low treatment, i.e. 730CF (
When using Schopper Grass 14.3), the tear strength increases significantly with increasing starch content. Therefore, it is thought that a moderate level of refiner treatment will produce little effect. That this is true can be seen from another experiment carried out on potato starch (see Figure 5), where the effect of increasing starch on tear strength is much smaller. Tear strength is a certain value (this probably varies depending on the pulp used)
It is thought that it will approach . The tear strength of untreated paper increases with increasing starch addition.

This is because it increases the fiber bonding and therefore the force required to separate the fibers during tearing. For the refiner-treated raw materials used in this study, it is believed that the best bonding to generate tearing was already achieved by the refiner-treated material. The added bonds created by starch therefore increase shear failure of the fibers,
Reduces tearing. The CD (machine direction or transverse direction) tear results are significantly better for the densified paper than for the non-densified paper in all cases;
This is because in CD tear strength, failure occurs across the densified fibers, and densified fibers with their smaller modulus and greater elongation are more difficult to shear than non-densified fibers. This can be explained by saying that there is. The initial increase in CD tear strength with increasing starch results from larger bonds and the difficulty of breaking these bonds. However, increasing the amount of starch results in increased fiber modulus and stiffness, further increasing bonding resulting in increased fiber shear failure and decreased tearing. As is usual for stretch papers, the MD tear strength is slightly lower than the CD value.

As mentioned above, the paper stock treated with the refiner loses its tear strength as starch is added (see Figure 6). If we now turn our attention directly to the properties improved by the addition of starch, we find that
That is, the tensile strength, stiffness, and TEA in Figure 7 are the MD for potato and corn starch at various concentrations.
The tensile strength results are shown. Each case was studied with two different refiner treatment degrees. The increase in tensile strength for potato starch occurred during the first 3% addition, but the increase in tensile strength with corn starch increased continuously as the amount added increased. . It has also been observed that adding 3% starch to densified paper increases the tensile strength to the extent of untreated (non-densified) paper. This can be understood by remembering that the molecular structure of corn starch, which has a more linear orientation than potato starch, gives rise to greater tensile strength. The use of corn starch at a high concentration (5%) doubles the stiffness of the densified sheet, making it closer to the untreated (non-densified) control. If you look at Figure 8, you can also see the results for potato starch. In this case, the increase is not dramatic at one intermediate refiner processing rate, which is common for bag paper production. It appeared that the best effect was achieved with the addition of 3% potato starch, with an increase in stiffness of about 40%.

Other properties increased by starch addition include studies to break in machine direction MD, TEA due to increased tensile strength (see Figure 9).

A 30% increase is evident when using corn starch, whereas only half of this can be obtained using the same amount of potato starch. Usually a 5-7 times increase in TEA (in MD) over non-densified paper (with and without starch treatment) appears. The significant difference in breaking strength is
Increasing starch addition did not result in a difference between densified and non-densified sheets. In any case, at a concentration of 3%, it is about 30~
A 40% increase was obtained. This was expected since the CD tensile strength, which affects bursting, and the TEA properties do not change significantly during the densification process. The result of the burst test therefore depends on the starch concentration. U.S. Pat. No. 3,362,869 describes applying a starch coating to one side of wet compacted paper, but this method destroys the purpose of the present invention, the mechanical properties of extensible paper. Without this, tensile strength, TEA, burst strength and stiffness cannot be obtained. This is illustrated in the following reference example. Reference Examples In each test, one side of a web of extensible (compacted) unbleached kraft paper having a moisture content of 22-28% by weight was coated with an aqueous solution of ground corn starch.

Starch solutions contain 1%, 4.15%, 5% or 10% starch
(Weight) Contained. In this way, one side of the paper web was coated with starch at 0.2% (in a 1% solution) and 0.7% (in a 4, 1% solution), respectively.
5% solution), 0.8% (in 5(!) solution) and 1.
6(!) (in a 10% solution). Keep the polishing roll at a high temperature of about 150-2501' and the nip pressure about 75
p1i and 600 p1i. The physical properties of the coated and polished extensible paper and the physical properties of the uncoated and unglazed extensible paper were measured. The results are shown in the table below.
From the above results, it was found that a stretchable paper web coated on one side with 0.2-1.6% (by weight) starch based on the paper (U.S. Pat. No. 33
No. 62869): - In general, the tensile strength increased only slightly (up to about 32% increase) and only about 15% increase with 1.6% starch addition.

TEA generally did not increase significantly (maximum increase was 16%)
, and there was no significant decrease (maximum decrease of about 34%), and at 1.6% starch addition, TEA decreased by 34%.

C] The crack strength generally did not significantly increase (maximum increase of about 25%) or decrease (maximum decrease of about 31%) in MD.
, tear strength MD decreased by about 16% when starch was added at 1.6%.

Tear strength generally decreased slightly (maximum decrease of about 23%) in CD, with 1.6% starch addition having a decrease of about 23%.

From above, according to US Pat. No. 3,362,869, starch 0.
Glazing a stretch paper coated on one side with 2-1.6% by weight results in a significant increase in tensile strength, TEA or tear strength compared to a control uncoated, unglazed stretch paper. It turns out that there is no improvement.

[Brief explanation of the drawing]

FIG. 1 is a schematic representation of a densification machine for producing extensible paper; FIG. 2 is a dryer section receiving the densified web after processing by the apparatus of FIG. 1 and applying a solution of starch to the web; FIG. 3 is a schematic diagram showing an alternative form of the invention in which the densified web is fed directly to the size press and from there to the dryer section; FIG. 4-9 show graphs of the effect of varying the percentage of starch on various strength factors for densified and non-densified papers. 10 is a densification machine, 40 is a size press, and 66 is a drying device.

Claims (1)

[Scope of Claims] 1. A paper web that is compressed and densified in the direction of web movement between pressure nips that densify and strengthen web fibers to produce inherent elongation without forming a crepe, the above-mentioned paper web impregnated on both sides with a predetermined amount of starch microparticles to contain 1 to 10% by weight starch on a dry basis, resulting in a substantially increased tensile strength compared to the same densified paper without starch impregnation, TEA; Paper web with improved strength with burst strength and stiffness. 2 The paper web is compressed and densified in the direction of web movement between the pressure nips that densify and strengthen the web fibers in a densification machine to produce inherent extensibility without crepe formation, and at this time, the web before densification The moisture content of the web is 20 to 50% by weight, and the moisture content of the web after densification is 35 to 45% by weight.
and then drying or not drying to bring the moisture content of the web after densification and before impregnation with starch solution from 1 to 40% by weight, and then applying the starch solution on both sides of the web under pressure on a dry basis. It is applied in an amount sufficient to impregnate a web having 1 to 10% by weight of starch, and the moisture content of the web during application of the starch solution is reduced to 35% after application of the starch solution.
A method for producing a paper web with improved strength properties characterized by controlling the starch content to ˜45% by weight and drying the starch impregnated paper web following impregnation.