JP2006257626A - Paper-container base paper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a paper-container base paper which is used as base paper for paper containers used for various drinks such as refreshing drinks, fruit drinks, coffee, beer, and tea and also as base paper for paper containers used for various foods such as fermented soybeans and yogurt, has excellent processing suitability into paper cups, gives the paper cups hardly collapsed, even when gripped, and has food printing suitability. <P>SOLUTION: This paper container base paper is characterized by containing pulp, as a pulp component preferably in an amount of ≥50 wt%, preferably having a Canada standard freeness of 100 to 400 ml, more preferably 200 to 350 ml, treated by bringing bubbles formed cavitation into contact with a pulp suspension. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a paper base paper having excellent paper cup processing suitability and good printability.

  Paper cups are used as containers for beverages such as soft drinks, fruit drinks, coffee, beer, and tea, and as containers for various foods such as natto and yogurt. Wax-impregnated paper has been partly used as base paper for beverage paper cups, but in recent years, polyethylene laminated paper (hereinafter referred to as polylaminated paper) in which one side of the paper is printed and the other side is laminated. ) Is mainly used. The paper cup is punched into a fan shape, which is the shape of the above-mentioned polylaminated paper developed into a cup, and both ends of the straight portion of the resulting fan-shaped polylaminated paper are bonded together with the laminate surface inside (called a cylinder-attached) cup-shaped It is manufactured by a series of operations in which a top curl process (a process of forming the mouth part of the cup) is performed by inserting a base paper into the bottom part and crimping it, and then winding the circumferential part of the upper end outward. The

  The speed of the molding machine used for the production of the above-mentioned paper cup has increased more and more in recent years. However, in order to produce an excellent quality paper cup at high speed and efficiently (hereinafter referred to as box-making property), it is used for polylaminated paper. The base paper is required to have a strength (hereinafter referred to as paper strength) that does not cause cracking even if the base paper is stretched by applying a large pulling force during the top curl process. In addition, characters and the like are printed on the surface of the paper cup and used as an advertisement. Therefore, in order to further improve the advertisement function, the paper cup surface is required to have excellent printability.

  Conventionally, as such a paper cup base paper, a base paper containing a large amount of softwood bleached kraft pulp (hereinafter referred to as NBKP) has been used from the viewpoint of imparting paper strength and improving box making (patent) Reference 1). However, NBKP is thicker and longer in fiber form compared to hardwood bleached kraft pulp (hereinafter referred to as LBKP), so when the amount of NBKP is increased, its paper strength is improved, but the texture is poor. It becomes uniform, and the flatness of the surface (referred to as surface property) deteriorates, so that the printability and polyethylene laminate suitability are inferior.

  In addition, there is a technique to promote pulp beating as a means of imparting paper strength and surface properties. However, if pulp is beaten too much, it loses bulk (higher density) and its stiffness decreases. When drinking, there was a drawback that the cup was crushed easily.

Patent No. 2960249

  An object of the present invention is to provide a paper base paper that is excellent in paper cup processing suitability, is not easily crushed even when a cup is gripped, and has good printability.

  The present inventors pay attention to the fact that the bulk of the pulp fiber itself is the lowest during the mechanical beating process, and selectively exerting a load on the pulp fiber surface to suppress the fiber damage and the progress of internal fibrillation. As a result of intensive research on methods that can suppress the decrease in bulk even when the pulp fiber is beaten, bubbles are generated by cavitation in the pulp suspension, and the pulp is brought into contact with the pulp suspension. By processing, it discovered that a pulp with little reduction in bulk could be obtained even if beating progressed, and found that a subject could be achieved.

  According to the present invention, it is possible to obtain a paper base paper that is excellent in paper cup processing suitability, is not easily crushed when a cup is gripped, and has good printability.

  Hereinafter, the present invention will be described in detail. The paper base paper of the present invention uses a pulp that is treated by bringing bubbles generated by cavitation in the pulp suspension into contact with the pulp suspension (hereinafter referred to as cavitation treatment). Normally, pulp is beaten using a mechanical force with a refiner or the like, but beating using mechanical force promotes fibrillation to the inside of the pulp fiber. In the present invention, cavitation is generated in the pulp fiber suspension, and the freeness is adjusted by the collapsing impact force of the fine bubbles generated by the cavitation. As a characteristic of the pulp treated by this method, a load is selectively applied to the pulp fiber surface, so that the pulp fiber cutting (damage) and the progress of internal fibrillation that have occurred due to beating by mechanical force are suppressed. The bulk of the pulp fiber can be maintained.

  In the present invention, the pulp to be subjected to cavitation treatment is made from conifers, hardwoods, non-wood fibers, or the like. More specifically, chemical pulp such as kraft pulp, mechanical pulp such as crushed wood pulp, thermomechanical pulp, chemithermomechanical pulp, or recycled pulp produced from a sheet-like substance made of waste paper or fiber. . Examples of used paper include newspapers, flyers, magazines for coated paper, magazines for coated paper, thermal recording paper, pressure-sensitive recording paper, imitation paper, colored fine paper, electrophotographic transfer paper, computer output paper, or these Applicable to mixed waste paper.

  Since cavitation occurs when a liquid is accelerated and the local pressure is lower than the vapor pressure of the liquid, flow rate and pressure are particularly important. From this, the basic dimensionless number representing the cavitation state, the cavitation number σ, is defined as follows (edited by Yoji Kato, new edition of cavitation basics and recent advances, Tsuji Shoten, 1999).

(P _∞: pressure general flow, U _∞: flow rate of the general flow, p _v: fluid vapor pressure, [rho: the density of the fluid)
Here, a large number of cavitations indicates that the flow field is in a state where cavitation is difficult to occur. In particular, when cavitation is generated through a nozzle or orifice pipe such as a cavitation jet, the cavitation number σ is calculated from the following equation (2) from the nozzle upstream pressure p ₁ , the nozzle downstream pressure p ₂ , and the saturated vapor pressure p _v of the sample water. In the cavitation jet, the pressure difference between p ₁ , p _{2 and} p _v is large, and p ₁ >> p ₂ >> p _v , so the cavitation number σ is further (H. Soyama, J. Soc. Mat. Sci. Japan, 47 (4), 381 1998).

  The cavitation condition in the present invention is preferably such that the above-mentioned cavitation number σ is 0.001 or more and 0.5 or less, preferably 0.003 or more and 0.2 or less, and particularly preferably 0.01 or more and 0.1 or less. When the cavitation number σ is less than 0.001, the effect is small because the pressure difference with the surroundings when the cavitation bubbles collapse is low, and when it is greater than 0.5, the flow pressure difference is low and cavitation is difficult to occur. .

  In addition, when the injection liquid is injected through the nozzle or the orifice tube to generate cavitation, the pressure of the injection liquid (upstream pressure) is desirably 0.01 MPa or more and 30 MPa or less, and 0.7 MPa or more and 15 MPa or less. It is particularly preferable that the pressure is 2 MPa or more and 10 MPa or less. When the upstream pressure is less than 0.01 MPa, it is difficult to produce a pressure difference from the downstream pressure, and the effect is small. On the other hand, when the pressure is higher than 30 MPa, a special pump and a pressure vessel are required, and energy consumption increases, which is disadvantageous in terms of cost.

  Further, the jet velocity of the jet liquid is desirably in the range of 1 m / second to 200 m / second, and preferably in the range of 20 m / second to 100 m / second. When the jet velocity is less than 1 m / second, the effect is weak because the pressure drop is low and cavitation hardly occurs. On the other hand, when it is higher than 200 m / sec, a high pressure is required and a special device is required, which is disadvantageous in terms of cost.

  Examples of cavitation generating means that can be used in the present invention include a method using a liquid jet, a method using an ultrasonic vibrator, a method using an ultrasonic vibrator and a horn-shaped amplifier, and a method using laser irradiation. Although not limited thereto, a method using a liquid jet is preferable because the generation efficiency of cavitation bubbles is high and a cavitation bubble cloud having a stronger collapse impact force is formed. Further, the cavitation treatment can be performed in an arbitrary container such as a tank or in a pipe, but is not limited thereto. Further, although it is possible to perform processing by one pass, the effect can be further increased by circulating the required number of times. Furthermore, it can be processed in parallel or in permutation using a plurality of generating means.

  In the method of generating cavitation by a liquid jet that can be used in the present invention, distilled water, tap water, industrial water, reused water recovered in the papermaking process, pulp squeezed water, white water, pulp Suspension, alcohol, and the like can be sprayed, but are not limited thereto. Preferably, spraying the pulp suspension itself is preferable because it is possible to circulate the whole amount of the pulp to be treated.

  Further, the pulp treatment concentration by cavitation in the present invention is preferably 5% by weight or less, more preferably 4% by weight or less, and further preferably in the range of 0.1 to 3% by weight. Processing in this range is preferable from the viewpoint of bubble generation efficiency.

  The cavitation treatment of the present invention can be applied to any place in the pulping process and the conditioning process, but it is preferable to apply it at the stage where the fibrous material is defibrated to become a pulp. Moreover, you may combine the beating process by the conventional beating machine by mechanical force, and the beating process by the cavitation of this invention.

  In the present invention, the pulp to be subjected to cavitation treatment is made from conifers, hardwoods, non-wood fibers, or the like. More specifically, chemical pulp such as kraft pulp, or mechanical pulp such as crushed wood pulp, thermomechanical pulp, and chemithermomechanical pulp can be used.

  The freeness of the cavitation-treated pulp used in the present invention is preferably 100 ml or more and 400 ml or less, more preferably 200 ml or more and 350 ml or less in Canadian standard freeness. If the Canadian standard freeness is less than 100 ml, the dewaterability of the wire part at the time of paper making is significantly reduced, which is not preferable because the paper making speed needs to be greatly reduced. On the other hand, when the Canadian standard freeness exceeds 400 ml, it is difficult to obtain the desired strength because the bonding area between the pulp fibers is lowered, and good printability cannot be obtained because the smoothness is lowered.

  The paper base paper of the present invention is required to use cavitation-treated pulp, but can also be mixed with pulp beaten by a general beater, for example, a disk-type, cone-type, or drum-type refiner. . However, in that case, the blending ratio of the cavitation-treated pulp is desirably 50% by weight or more in the pulp component. If the compounding ratio of the cavitation-treated pulp is less than 50% by weight, sufficient strength, stiffness and smoothness may not be obtained.

  In the paper base paper of the present invention, a sizing agent can be internally or externally added in the same manner as ordinary paper. In the case of acidic papermaking, the sizing agent may be rosin sizing agent, rosin emulsion sizing agent, alpha carboxymethyl saturated fatty acid, or the like. On the other hand, in the case of neutral papermaking, rosin sizing agents for neutral papermaking, alkyl ketene dimers, alkenyl succinic anhydrides, and cationic polymer sizing agents can be used.

  In addition, when necessary, when fixing, fixing agent, dry paper strength agent, wet paper strength agent, filler, yield improver, dyes, pigments and other internal chemicals, surface sizing agent, surface strength agent, dye, It is possible to add external additives such as pigments.

The basis weight of the paper base paper of the present invention depends on the size and shape of the cup, but is preferably 150 g / m ² or more and 400 g / m ² or less. If the basis weight is less than 150 g / m ² , the stiffness will be low and the cup will be crushed easily when holding a cup and drinking a beverage. On the other hand, if the basis weight exceeds 400 g / m ² , the curl radius on the inner surface of the top curl portion becomes smaller during top curl processing, so the compressive stress applied to the inner surface increases, causing buckling and cracking. It becomes easy.

  The Taber stiffness of the paper base paper of the present invention is preferably 4.5 mN · m or more and 30 mN · m or less. When the Taber stiffness is less than 4.5 mN · m, the stiffness is low, and the cup tends to be crushed when holding the cup and drinking a beverage. On the other hand, if the Taber stiffness exceeds 30 mN · m, the curl radius of the inner surface becomes smaller during top curl processing, so that the compressive stress applied to the inner surface increases and buckling and cracking are likely to occur.

  The paper base paper of the present invention is produced by a known paper machine, but the paper making conditions are not particularly specified. As the paper machine, a long net paper machine, a twin wire paper machine or the like is used.

  The paper base paper of the present invention is used as a base paper for containers for beverages such as soft drinks, fruit drinks, coffee, beer and tea, or containers for various foods such as natto and yogurt. It can also be used as a base paper for nursery pots.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not restrict | limited by this. In addition, "weight%" shown below shows the weight% with respect to the absolute dry weight of a pulp.
The following methods were used as evaluation methods for the paper base paper obtained in each example and comparative example.
-Basis weight: According to JIS P 8124.
-Density: According to JIS P 8118.
-Taber stiffness (paper making direction): compliant with JIS P 8125.
Box making test (paper cracking): When box making was performed using the obtained base paper, the presence or absence of paper cracking in the top curl portion of the paper cup was visually evaluated.
○: No paper breakage ×: Paper breakage ・ Printability test: A test gravure printing machine (manufactured by Kumagai Riki Co., Ltd.) was used to print on the base paper, and the printed state was evaluated visually.
○: Good ×: Inferior

[Example 1]
Using a cavitation jet cleaning apparatus (nozzle diameter 1.5 mm) as shown in FIG. 1, the pressure of the jet liquid is 7 MPa (jet flow velocity 70 m / sec), the pressure in the jetted container is 0.3 MPa, Use pulp suspension of hardwood bleached kraft pulp (LBKP) at a concentration of 1.1% by weight for pulp suspension in the container, and beat the pulp by cavitation so that the Canadian standard freeness (CSF) is 250 ml. Performed (pulp A). A rosin sizing agent (trade name: Size Pine E-50, manufactured by Arakawa Chemical Industries, Ltd.) is added to the obtained pulp A slurry so that the solid content becomes 0.7 wt%, and the pH of the slurry becomes 4.5. After adding the sulfuric acid band as described above, paper was made with a long web paper machine to obtain a paper base paper having a basis weight of 200 g / m ² . With respect to the obtained paper base paper, the basis weight, density, and Taber stiffness were measured, and the box making properties and printability were evaluated. The results are shown in Table 1.

[Example 2]
Using a double disc refiner (hereinafter referred to as DDR), softwood bleached kraft pulp (NBKP) was beaten so that the Canadian standard freeness (CSF) was 400 ml (pulp B). Then, paper was made in the same manner as in Example 1 except that a pulp slurry in which Pulp A and Pulp B were mixed at a weight ratio of 80:20 was used to obtain a paperboard base paper. With respect to the obtained paper base paper, the basis weight, density, and Taber stiffness were measured, and the box making properties and printability were evaluated. The results are shown in Table 1.

[Comparative Example 1]
Using DDR, LBKP was beaten so that the Canadian standard freeness (CSF) was 250 ml (pulp C). A paper base paper was obtained by making paper in the same manner as in Example 1 except that Pulp C was used as the raw material slurry. With respect to the obtained paper base paper, the basis weight, density, and Taber stiffness were measured, and the box making properties and printability were evaluated. The results are shown in Table 1.

[Comparative Example 2]
Using DDR, LBKP was beaten so that the Canadian standard freeness (CSF) was 380 ml (pulp D). Papermaking was carried out in the same manner as in Example 1 except that pulp D was used as a raw material slurry to obtain a paper base paper. With respect to the obtained paper base paper, the basis weight, density, and Taber stiffness were measured, and the box making properties and printability were evaluated. The results are shown in Table 1.

[Comparative Example 3]
Paper base paper was obtained in the same manner as in Example 1 except that pulp B and pulp D were mixed at a weight ratio of 50:50 to obtain a raw material pulp slurry. With respect to the obtained paper base paper, the basis weight, density, and Taber stiffness were measured, and the box making properties and printability were evaluated. The results are shown in Table 1.

  As shown in Table 1, Examples 1 and 2 have good stiffness, paper cracking, and printability, while Comparative Example 1 has low stiffness, Comparative Example 2 has paper cracking, and Comparative Example 3 has printability. Were insufficient. From this result, it is possible to obtain a paper base paper that is excellent in paper cup processing suitability by using a cavitation-treated pulp, is not easily crushed even when the cup is gripped, and has good printability.

It is the schematic of the cavitation jet type washing | cleaning apparatus used in the Example.

Explanation of symbols

1: Sample tank 2: Nozzle 3: Cavitation jet cell 4: Plunger pump 5: Upstream pressure control valve 6: Downstream pressure control valve 7: Upstream pressure gauge 8: Downstream pressure gauge 9: Water supply valve 10: Circulation valve 11: Drain valve 12: Temperature sensor 13: Mixer

Claims (3)

A paper base paper comprising pulp produced by generating bubbles by cavitation in a pulp suspension and contacting the pulp suspension with the bubbles. The paper container base paper according to claim 1, wherein the Taber stiffness is 4.5 mN · m or more and 30 mN · m or less. The paper base paper according to claim 1 or 2, wherein the basis weight is 150 g / m ² or more and 400 g / m ² or less.

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