JP2023121209A - Kraft paper - Google Patents

Abstract

To provide kraft paper which exhibits excellent handleability when used as packaging paper, and exhibits excellent adhesion to resin when laminated.SOLUTION: Kraft paper contains unbleached soft wood kraft pulp and bleached soft wood kraft pulp, and a sizing agent, a paper strengthening agent and aluminum sulfate, and does not substantially contain a loading material, wherein the total content of the unbleached soft wood kraft pulp and the bleached soft wood kraft pulp with respect to pulp is 90 mass% or more, and a content mass ratio of the unbleached soft wood kraft pulp to the bleached soft wood kraft pulp is 65:35 to 90:10.SELECTED DRAWING: None

Description

The present invention relates to kraft paper containing kraft pulp. In particular, it relates to kraft paper useful for wamp applications.

Kraft paper is paper having excellent strength, which is made from pulp produced by the Kraft method. Kraft paper is used, for example, for wrapping paper, paper bags, envelopes, corrugated board materials and adhesive tapes. Among wrapping papers and paper bags, there are wamps, handbags, and the like that are laminated with a resin in order to impart strength and barrier properties (see, for example, Patent Documents 1 and 2).
Kraft paper that can be preferably used for heavy bags that can be efficiently filled with powder products, contains hardwood kraft pulp, and has a transverse breaking elongation of 7.0 measured according to JIS P8113. % or more, an elongation at break in the machine direction of 5.0% or more, and an air permeability of 5 to 60 seconds as measured according to JIS P8117 (see, for example, Patent Document 3).

Patent No. 6935002 JP 2017-214104 A JP 2015-124464 A

For example, in a packaging operation, there is a case where wrapping paper such as kraft paper is folded so as to fit the shape of an object to be stored. In such a packaging operation, the kraft paper naturally needs to have tear strength so that it does not tear, and it is also required to have handleability such as easy fitting to the stored items. Further, for example, kraft paper for wrapping paper is laminated to protect the paper from moisture and the like.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a kraft paper which is excellent in handleability as a wrapping paper and excellent in adhesiveness to a resin in lamination.

The object of the present invention can be achieved by the following kraft paper.
[1] Containing unbleached softwood kraft pulp and bleached softwood kraft pulp, as well as a sizing agent, a paper strength agent, and aluminum sulfate, and containing substantially no filler, the unbleached softwood kraft pulp and the bleached softwood kraft pulp The total content is 90% by mass or more based on the pulp, and the content ratio by mass of the unbleached softwood kraft pulp and the bleached softwood kraft pulp is unbleached softwood kraft pulp:bleached softwood kraft pulp = 65:35 to 90: Kraft paper that is 10.

[2] The kraft paper according to [1] above, wherein the unbleached softwood kraft pulp has a freeness of 500 mlcsf or more and the bleached softwood kraft pulp has a freeness of 400 mlcsf or more and 500 mlcsf or less.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide kraft paper which is excellent in handleability as wrapping paper and excellent in adhesion to resin in lamination.

The present invention will be described in detail below.

The kraft paper contains at least softwood unbleached kraft pulp and softwood bleached kraft pulp, as well as a sizing agent, a paper strength agent, and aluminum sulfate.
Furthermore, the kraft paper can contain conventionally known additives in the papermaking field other than those mentioned above. Examples of additives include fillers, fixing agents, retention agents, water resistance agents, dispersants, thickeners, fluidity improvers, defoaming agents, foam inhibitors, release agents, foaming agents, penetrating agents, and coloring agents. agents, optical brighteners, UV absorbers, antioxidants, preservatives, and anti-fungal agents.

Kraft paper contains substantially no fillers. Fillers generally have the effect of reducing the strength of the paper. Here, "substantially" means that the filler is not contained in an amount that reduces the strength of the paper. Kraft paper may contain fillers in small amounts that do not reduce the strength of the paper. In some embodiments, the kraft paper contains no fillers.

Fillers are white inorganic pigments conventionally known in the paper industry. Examples of fillers include kaolin, clay, light calcium carbonate, heavy calcium carbonate, talc, titanium dioxide, satin white, aluminum silicate, diatomaceous earth, calcium silicate, synthetic amorphous silica, colloidal silica, aluminum hydroxide and alumina. can be mentioned.

The filler content in kraft paper can be estimated in terms of ash content. The ash content depends on the content of fillers contained in the kraft paper and the metal components of inorganic salts such as aluminum sulfate.
In some embodiments, the kraft paper has an ash content of 2% by weight or less, determined according to ISO 1762:2001 "Paper, board and pulps—Determination of residue (ash) on ignition at 525 degrees C". In at least one embodiment, the kraft paper has an ash content of no less than 0.3% and no more than 2% by weight, depending on the aluminum sulfate.

Kraft paper is produced by mixing a slurry of kraft pulp in water with a sizing agent, a strength agent, aluminum sulfate, and, if necessary, other additives. Paper is made using a conventionally known paper machine such as a twin wire paper machine, and a surface sizing agent such as starch, polyvinyl alcohol, styrene acrylic resin or olefin maleic acid resin is added to the resulting paper as necessary. and/or calendering with a machine calender, soft nip calender, super calender, multi-stage calender or multi-nip calender.

The size press process is performed using a size press apparatus conventionally known in the papermaking field. Examples of size press equipment include an incline size press, a horizontal size press, a rod metering size press, a roll metering size press, and a blade metering size press as film transfer systems, and a shim sizer and an optimizer as rod metering size presses. , a speed sizer, a film press, and a gate roll coater as a roll metering size press. Further, bill blade coaters, twin blade coaters, velvapa coaters, tab size presses, calender size presses and the like can be mentioned.

Kraft pulp is a kind of chemical pulp produced by conventionally known kraft methods in the field of papermaking. Bleached kraft pulp is kraft pulp that has been bleached by a bleaching process. Unbleached kraft pulp is kraft pulp that has not undergone the bleaching process.
Pulp raw materials include conventionally known wood or non-wood, such as coniferous and broad-leaved wood, hemp, linter, straw, bamboo, sugar cane, reeds, fruits, paper mulberry, mitsumata, and gampi. can be done. Bleached kraft pulp is referred to as softwood bleached kraft pulp if the pulp raw material is softwood, and unbleached kraft pulp is referred to as softwood unbleached kraft pulp if the pulp raw material is softwood.

Kraft paper includes conventionally known unbleached softwood kraft pulp, bleached softwood kraft pulp, unbleached hardwood kraft pulp, bleached hardwood kraft pulp, semi-bleached softwood kraft pulp, semi-bleached hardwood kraft pulp, mechanical pulp, and deinked waste paper pulp. It can contain pulp.
The kraft paper has a total content of unbleached softwood kraft pulp and bleached softwood kraft pulp of 90% by mass or more relative to the pulp in the kraft paper. In some embodiments, the kraft paper has a total content of softwood unbleached kraft pulp and softwood bleached kraft pulp of 100% by mass based on the pulp in the kraft paper. The reason for this is that the handling property as wrapping paper and the adhesiveness to the resin in the laminating process are improved.
Further, the kraft paper contains unbleached softwood kraft pulp and bleached softwood kraft pulp in a mass ratio of unbleached softwood kraft pulp:bleached softwood kraft pulp=65:35 to 90:10. If the softwood bleached kraft pulp is less than the above range, the handleability as wrapping paper and adhesiveness to resin during lamination tend to deteriorate. When the content of bleached softwood kraft pulp exceeds the above range, the tear strength of the paper tends to decrease.
In general kraft paper, unbleached kraft pulp is used to obtain paper strength, and the unbleached kraft pulp accounts for 100% by mass of the pulp in the kraft paper. Further, as the unbleached kraft pulp, unbleached softwood kraft pulp is used because of its long fiber length. However, kraft paper containing 100% by mass of unbleached kraft pulp has difficulty in handling as wrapping paper and adhesion to resin in lamination. The present inventors have found that these problems can be solved by blending an appropriate amount of bleached kraft pulp.

In some embodiments, the freeness of the unbleached softwood kraft pulp contained in the kraft paper is 500 mlcsf or more, and the freeness of the bleached softwood kraft pulp is 400 mlcsf or more and 500 mlcsf or less. The reason for this is that the tear strength, the handleability as wrapping paper, and the adhesiveness to the resin in the laminating process are improved.
The freeness is a value determined according to ISO5267-2:2001 "Pulps-Determination of drainage-Part 2: Canadian Standard Freeness method". Freeness can be adjusted by beating and/or refining the pulp. As the beating and/or refining of the pulp proceeds, the freeness value decreases. The upper limit of the freeness of softwood unbleached kraft pulp, which has a freeness in the range of 500 mlcsf or more, is the freeness of pulp that is not subjected to beating and/or refining. The upper freeness limit of typical unbleached softwood kraft pulp ranges from 680 mlcsf to 740 mlcsf.

A sizing agent is an internal sizing agent used in the papermaking process to impart sizing properties. The sizing agent is conventionally known in the papermaking field and is not particularly limited. Examples of sizing agents include rosin-based sizing agents for acidic paper, alkenyl succinic anhydride-based sizing agents for neutral paper, alkylketene dimer-based sizing agents, neutral rosin-based sizing agents, fatty acid-based sizing agents, and cationic styrene-acrylic resin-based sizing agents. In some embodiments, the size is a rosin-based size. The reason for this is that the sizing properties of kraft paper obtained by making a paper stock containing substantially no filler can be stably exhibited.
The content of the sizing agent in the kraft paper may be conventionally known in the papermaking field. The content of the sizing agent is, for example, 1 part by mass or more and 20 parts by mass or less with respect to 1000 parts by mass of the pulp contained in the kraft paper.

A paper strength agent is also called a paper strength agent, and is an internal paper strength agent used in the papermaking process to impart strength to paper. The paper strength agent is conventionally known in the papermaking field and is not particularly limited. Examples of paper strength agents include starches and modified starches such as dialdehyde starch, oxidized starch and cationic starch, vegetable gums such as guar gum, locust bean gum and tragacanth gum, methylcellulose, carboxymethylcellulose, hydroxymethylcellulose and hydroxyethylcellulose. and synthetic polymers such as polyurethane-based resins, polyethyleneimine-based resins, urea-based resins, polyethylene oxide-based resins and polyvinyl alcohol-based resins.
In some embodiments, the strength agents are starches and modified starches such as dialdehyde starches, oxidized starches and cationic starches. In at least one embodiment, the strength agent is cationic starch. The reason for these is that the printability tends to improve when printing on kraft paper.
The paper strength agent in the kraft paper may be any content that is conventionally known in the papermaking field. The content of the paper strength agent is, for example, 5 parts by mass or more and 30 parts by mass or less with respect to 1000 parts by mass of the pulp contained in the kraft paper.

Aluminum sulphate has an effect on the fixing of the sizing agent into the paper. In particular, it is effective when the sizing agent is the rosin-based sizing agent. The aluminum ions of aluminum sulfate can bond with the fibers of the pulp, thus increasing the strength of the paper. However, if aluminum sulfate is contained, the paper is acidified and easily degraded. This limits the content of aluminum sulphate.

In some embodiments, the kraft paper contains retention agents conventionally known in the papermaking arts. Retention agents are, for example, cationic resins or anionic resins. The cationic resin that serves as a retention agent is a resin containing primary to tertiary amines or quaternary ammonium salts that easily coordinate with protons and dissociate when dissolved in water to exhibit cationic properties. Cationic resins include, for example, polyethyleneimine, polyvinylpyridine, polyaminesulfone, polydialkylaminoethyl methacrylate, polydialkylaminoethyl acrylate, polydialkylaminoethyl methacrylamide, polydialkylaminoethyl acrylamide, polyepoxyamine, polyamidoamine, dicyandiamide- Formalin condensate, dicyandiamide polyalkyl-polyalkylenepolyamine condensate, polyvinylamine, compounds such as polyallylamine and salts thereof, diallylamine acrylamide copolymer, polydiallylmethylamine hydrochloride, poly(diallyldimethylammonium chloride), poly (diallyldiethylammonium chloride), copolymer of diallyldimethylammonium chloride and acrylamide, copolymer of diallyldimethylammonium chloride and methacrylamide, copolymer of diallyldiethylammonium chloride and acrylamide, copolymer of diallyldiethylammonium chloride and methacrylamide Polymers, dimethylamine ammonia epichlorohydrin copolymers, diethylamine epichlorohydrin ammonia copolymers and the like can be mentioned.
In some embodiments, the retention agent is an acrylamide-based resin containing acrylamide and/or methacrylamide as monomers constituting the resin. The reason for this is that the handleability as wrapping paper is improved.

The content of the retention agent in the kraft paper may be conventionally known in the papermaking field. The content of the retention agent is, for example, 0.05 parts by mass or more and 1 part by mass or less with respect to 1000 parts by mass of the pulp contained in the kraft paper.

In some embodiments, the kraft paper contains softwood unbleached kraft pulp and softwood bleached kraft pulp, as well as a sizing agent, a paper strength agent, aluminum sulfate, and an acrylamide-based resin, and is substantially free of fillers. The total content of the unbleached softwood kraft pulp and the bleached softwood kraft pulp is 90% by mass or more relative to the pulp, and the content ratio of the unbleached softwood kraft pulp to the bleached softwood kraft pulp is the unbleached softwood kraft pulp : Softwood bleached kraft pulp = 65:35 to 90:10.
In at least one embodiment, the kraft paper contains softwood unbleached kraft pulp and softwood bleached kraft pulp, as well as a sizing agent, a paper strength agent, aluminum sulfate, and an acrylamide-based resin, and is substantially free of fillers. The total content of the unbleached softwood kraft pulp and the bleached softwood kraft pulp is 90% by mass or more relative to the pulp, and the content ratio of the unbleached softwood kraft pulp to the bleached softwood kraft pulp is the unbleached softwood kraft pulp : Bleached softwood kraft pulp = 65:35 to 90:10, the freeness of the unbleached softwood kraft pulp is 500 mlcsf or more, and the freeness of the bleached softwood kraft pulp is 400 mlcsf or more and 500 mlcsf or less.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded. In addition, mass % and mass parts shown in the examples represent values of dry solid content or substantial components. The applied amount of the surface sizing agent indicates the value of the dry solid content.

<kraft paper>
A rosin sizing agent (Seiko PMC Co., Ltd., CC-1404 ) as a paper strength agent, 15 parts by mass of cationized starch (CHARGEMASTER R462, Grain Processing Corporation), 10 parts by mass of aluminum sulfate, and an acrylamide resin (Hymo Co., Himolock (registered trademark) as a retention agent ND300) was mixed with 0.1 part by mass to prepare a stock. The stock was made into paper using a Fourdrinier paper machine to obtain paper having a basis weight of 64 g/m ² . Both sides of the paper were size-pressed with a size press liquid containing oxidized starch (Oji Cornstarch Co., Ltd., Oji Ace A) and styrene acrylic resin (Arakawa Chemical Industries, Ltd., Polymaron (registered trademark) 1308S) as a surface sizing agent. processed. The amount of surface sizing agent applied was 0.3 g/m ² for oxidized starch and 0.07 g/m ² for styrene-acrylic resin per side. The ash content was 1.5% by weight.

The parts by weight and freeness (mlcsf) of unbleached kraft pulp and bleached kraft pulp are listed in Table 1.
In Table 1, unbleached softwood kraft pulp is denoted by NUKP, bleached softwood kraft pulp by NBKP, unbleached hardwood kraft pulp by LUKP, and bleached hardwood kraft pulp by LBKP.

<Strength of kraft paper (“strength of paper” in Table 1)>
The strength of the kraft paper was evaluated using the value of tear strength measured according to ISO1974:1990 "Paper-Determination of tearing resistance (Elmendorf method)". The strength of kraft paper was evaluated based on the specific tear strength calculated by the following formula in order to eliminate the influence of basis weight. The measurements were made in the MD direction of the kraft paper.
Specific tear strength (mN m ² /g) = [tear strength (mN)/basis weight (g/m ² )]
Evaluation was performed according to the following criteria. In the present invention, if the kraft paper is rated A or B, it is assumed to have strength.
A: Specific tear strength of 9 mN·m ² /g or more B: Specific tear strength of 7 mN·m ² /g or more and less than 9 mN·m ² /g C: Specific tear strength of less than 7 mN·m ² /g

<Handleability as wrapping paper (“Handleability” in Table 1)>
As an object to be wrapped with kraft paper, a circular paper tube type (A2, inner diameter 60 mm) manufactured by Kokuyo Co., Ltd. was prepared. There were five test subjects, and each of the test subjects carried out the wrapping work on the round tube by the tube wrapping method. Each subject sensorily evaluated the handleability of the packaging from the viewpoint of the fit to the shape of the object to be packaged and the workability of bending and folding the kraft paper in the following 5 stages. The final evaluation results were obtained by calculating the average value of the 5 subjects and rounding off to the nearest whole number. In the present invention, kraft paper with an evaluation of 3 points or more is considered to be excellent in handleability as wrapping paper.
5 points: Very good.
4 points: Good.
3 points: Generally good.
2 points: Normal.
1 point: inferior.

<Adhesiveness with resin in lamination (“adhesiveness” in Table 1)>
One side of the kraft paper was laminated with low-density polyethylene using a melt-extrusion die so as to have a thickness of 15 μm. Kraft paper was cut to a width of 50 mm, and the interface between the kraft paper and the laminate layer was made to form a T-shaped peel. The peel strength to the interface was measured. Based on the measurement results, the adhesion was evaluated according to the following criteria. In the present invention, if the kraft paper is graded A or B, it is considered to have excellent adhesiveness to the resin in lamination.
A: 0.6 N/50 mm or more B: 0.3 N/50 mm or more and less than 0.6 N/50 mm C: less than 0.3 N/50 mm

Table 1 shows the evaluation results of Examples and Comparative Examples.

From Table 1, it can be seen that Examples 1 to 13, which satisfy the configuration of the present invention, have tear strength, are excellent in handleability as wrapping paper, and are excellent in adhesion to resins in lamination. On the other hand, it can be seen that Comparative Examples 1 to 5, which do not satisfy the constitution of the present invention, cannot obtain any of the above effects.
Mainly from the comparison between Examples 4 to 12, when the freeness of the softwood unbleached kraft pulp is 500mlcsf or more and the freeness of the softwood bleached kraft pulp is 400mlcsf or more and 500mlcsf or less, tear strength, packaging It can be seen that the handleability as paper and the adhesiveness to the resin are improved in the lamination process.

Claims (2)

The total content of the unbleached softwood kraft pulp and the bleached softwood kraft pulp, and the unbleached softwood kraft pulp and the bleached softwood kraft pulp containing a sizing agent, a paper strength agent, and aluminum sulfate and substantially free of fillers is 90% by mass or more of the pulp, and the content ratio of the unbleached softwood kraft pulp and the bleached softwood kraft pulp is unbleached softwood kraft pulp:bleached softwood kraft pulp = 65:35 to 90:10. kraft paper. 2. The kraft paper according to claim 1, wherein the softwood unbleached kraft pulp has a freeness of 500 mlcsf or more and the freeness of the softwood bleached kraft pulp is 400 mlcsf or more and 500 mlcsf or less.