JP7623170B2 - Paper label base paper - Google Patents

Description

The present invention relates to paper label base paper for making paper labels for use on beverage bottles, etc.

Plastics are widely used as a material for various products because they are inexpensive and easy to mold, and more than 300 million tons of plastic products are produced each year.
Although most plastic products are disposed of properly, some end up in the environment as litter due to inadequate management or illegal dumping, and eventually reach the ocean. It is estimated that more than 8 million tons of plastic litter ends up in the ocean every year, and because most of this plastic litter is non-biodegradable, most of it accumulates in the ocean.

There is a growing movement to prevent environmental destruction caused by plastic waste, and there is a demand to improve the recycling rate of disposable plastic products. For example, a collection system for PET bottles, a typical disposable plastic product, has been established in Japan, and in fiscal year 2018, 25.2 billion PET bottles were sold, with a recycling rate (recycled amount/sales amount) of 91.5% (Non-Patent Document 1).
On the other hand, labels that are wrapped around PET bottles and the like to indicate product names, ingredients, etc. are made of various materials such as polystyrene, polypropylene, and PET, and are therefore not suitable for recycling. For this reason, it is estimated that in Japan, as many as 25.2 billion labels, roughly equivalent to the number of PET bottles sold, were disposed of as waste in fiscal 2018.

As an alternative material with less environmental impact to fossil-derived plastics, bio-derived plastics and biodegradable plastics have been attracting attention, as well as paper. However, PET bottles, especially for beverages, can have their labels wet due to spills or condensation, and furthermore, they can be immersed in ice water to cool them down during outdoor events.
Generally, papermaking fibers such as pulp that constitute paper tend to be oriented along the direction in which the paper flows during papermaking in a papermaking machine, etc., and it is known that various paper strengths such as tensile strength have different values in the direction in which the paper flows during papermaking (hereinafter referred to as MD direction) and the direction perpendicular thereto (hereinafter referred to as CD direction). Therefore, paper having various paper strengths in the MD direction and CD direction that are suitable for the intended use is selected, but when the paper is used as a label, as described above, the label may be immersed in ice water to cool it, and therefore the paper is required to have very high water resistance in both the MD direction and the CD direction.

PET Bottle Recycling Promotion Council, "Calculating the recycling rate," [online], Internet <URL: http://www.petbottle-rec.gr.jp/data/calculate.html>

The objective of the present invention is to provide a base paper for paper labels with excellent water resistance for producing paper labels that can be used on beverage bottles, etc. as an alternative to plastic labels.

The means for solving the problems of the present invention are as follows.
1. A base paper for a paper label, characterized in that the wet specific tensile strength in either the MD direction, the CD direction, or both is 10 kNm/kg or more.
2. The base paper for paper labels according to 1., characterized in that the wet specific tensile strength is 10 kNm/kg or more in both the MD and CD directions.
3. The base paper for paper labels according to 1. or 2., characterized in that the basis weight is 18 g/ ^m2 or more and 100 g/m2 or ^less .
4. The paper label base paper according to any one of 1. to 3., characterized in that the bending resistance in the MD direction measured in accordance with JIS P8125-1:2017 is 3.0 mN or more and 50 mN or less.

The paper label base paper of the present invention has excellent water resistance and is not easily torn even when wet. The paper label base paper of the present invention can be suitably used as the base paper for paper labels used for beverage bottles, seasoning bottles, etc.

The present invention will be described in detail below.
The base paper for paper labels of the present invention (hereinafter also referred to as base paper) has a wet tensile strength index of 10 kNm/kg or more in either or both of the MD and CD directions. The base paper of the present invention has a wet tensile strength index of 10 kNm/kg or more in either or both of the MD and CD directions, and is excellent in paper strength in a wet state. The base paper of the present invention preferably has a wet tensile strength index of 10 kNm/kg or more in both the MD and CD directions. Base paper having a wet tensile strength index of 10 kNm/kg or more in both the MD and CD directions is less likely to break even when forces are applied from various directions such as up, down, left and right in a wet state, and can be further preferably used as a base paper for paper labels used for beverage bottles. In this specification, the wet tensile strength index is a value obtained by dividing the wet tensile strength measured with an immersion time of 24 hours in accordance with the general method of JIS P8135:1998 by basis weight.
The base paper of the present invention preferably has a wet tensile index of 12 kNm/kg or more, more preferably 15 kNm/kg or more, in both the MD and CD directions. Furthermore, the base paper of the present invention preferably has a wet tensile index of 20 kNm/kg or more, more preferably 25 kNm/kg or more, in the MD direction. Furthermore, the base paper of the present invention preferably has a wet tensile index of 12 kNm/kg or more, more preferably 15 kNm/kg or more, in the CD direction.

The wet tensile strength of the base paper of the present invention, measured in accordance with the general method of JIS P8135:1998 with an immersion time of 24 hours, is preferably 0.5 kN/m or more in the MD direction, more preferably 0.6 kN/m or more, and even more preferably 0.8 kN/m or more. Also, in the CD direction, it is preferably 0.1 kN/m or more, more preferably 0.3 kN/m or more, and even more preferably 0.4 kN/m or more.

The base paper of the present invention has a tensile index (hereinafter referred to as dry tensile index) measured in accordance with JIS P8113:1998 of preferably 80 kNm/kg or more in the MD direction, more preferably 100 kNm/kg or more. Also, in the CD direction, it is preferably 40 kNm/kg or more, more preferably 50 kNm/kg or more. Also, the tensile strength (hereinafter referred to as dry tensile strength) measured in accordance with JIS P8113:1998 is preferably 1.8 kN/m or more in the MD direction, more preferably 2.0 kN/m or more, and even more preferably 2.5 kN/m or more. Also, in the CD direction, it is preferably 0.8 kN/m or more, more preferably 1.2 kN/m or more, and even more preferably 1.5 kN/m or more.
The ratio of wet tensile strength to dry tensile strength (wet tensile strength/dry tensile strength) in the MD is preferably 0.25 or more, more preferably 0.3 or more, and in the CD is preferably 0.15 or more, more preferably 0.25 or more, even more preferably 0.3 or more.

Furthermore, the base paper of the present invention preferably has a bending resistance value in the MD direction measured in accordance with JIS P8125-1:2017 of 3.0 mN or more and 50 mN or less. When the bending resistance value in the MD direction is within the above range, the paper is easy to handle when wound around a bottle or the like using a machine, and breaks in the paper or poor winding are unlikely to occur. The bending resistance value in the MD direction is more preferably 5.0 mN or more, and even more preferably 8.0 mN or more.

The base paper for paper labels of the present invention comprises pulp, fillers, various auxiliary agents such as wet strength materials, and the like.
The pulp may be any of a variety of known pulps, including chemical wood pulps such as bleached softwood kraft pulp (NBKP), unbleached softwood kraft pulp (NUKP), bleached hardwood kraft pulp (LBKP), unbleached hardwood kraft pulp (LUKP), and sulfite pulp (SP); mechanical wood pulps such as ground pulp (GP), refiner ground pulp (RGP), stone ground pulp (SGP), chemi-ground pulp (CGP), semi-chemical pulp (SCP), thermomechanical pulp (TMP), and chemi-thermomechanical pulp (CTMP); non-wood pulps obtained from kenaf, bagasse, bamboo, hemp, straw, and the like; and waste paper pulp made from waste paper, from which the ink contained in the waste paper has been removed in a deinking process.

Among these, in terms of price, ease of availability, ease of tearing when removed from the container, etc., it is preferable that the total amount of pulp contains 50% or more by weight of wood pulp, and more preferably contains 50% or more by weight of softwood pulp (NP) relative to the total amount of pulp. By making the softwood pulp 50% or more by weight, the strength of the base paper can be increased and durability can be improved. The ratio of softwood pulp to the total amount of pulp is more preferably 60% or more by weight, and even more preferably 80% or more by weight. As the softwood pulp, softwood bleached kraft pulp (NBKP) and softwood unbleached kraft pulp (NUKP) can be suitably used. Generally, paper with stronger paper strength can be produced by using unbleached pulp that has not been bleached rather than bleached bleached pulp. However, since the present invention can obtain a base paper with high wet strength, the effect of the present invention can be greatly enjoyed when bleached pulp with weak paper strength is used.

The freeness (Canadian Standard Freeness: CSF) of the raw material pulp of the present invention is not particularly limited, but is preferably 200 ml to 600 ml, more preferably 250 ml to 500 ml. In the present invention, when multiple types of raw material pulp are used, the multiple raw material pulps may be beaten separately or mixed and beaten.

Fillers that can be used include known fillers such as inorganic fillers such as talc, kaolin, calcined kaolin, clay, heavy calcium carbonate, light calcium carbonate, white carbon, zeolite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, barium sulfate, and calcium sulfate, and organic fillers such as urea-formaldehyde resin, polystyrene resin, phenolic resin, and hollow microparticles. Note that fillers are optional and do not have to be used, and if used, it is preferable to use a small amount.

The base paper of the present invention may contain various other auxiliary agents within the range that does not impair the effects of the present invention. For example, sizing agents such as rosin, alkyl ketene dimer (AKD), and alkenyl succinic anhydride (ASA), polyacrylamide polymers, polyvinyl alcohol polymers, cationic starch, various modified starches, dry strength agents such as urea-formaldehyde resin and melamine-formaldehyde resin, wet strength agents, retention agents, drainage improvers, coagulants, aluminum sulfate, bulking agents, dyes, fluorescent whitening agents, pH adjusters, defoamers, ultraviolet protection agents, anti-fading agents, pitch control agents, slime control agents, etc. may be appropriately selected and used as needed.

The base paper of the present invention preferably contains a wet strength agent. As the wet strength agent, one or a mixture of two or more of polyamide polyamine epichlorohydrin resin, polyamine epichlorohydrin resin, polyamide epichlorohydrin resin, polyvinylamine resin, polyethyleneimine resin, etc. can be used. Among these, it is preferable to use polyamine epichlorohydrin resin because it has excellent paper strength when wet.

The wet strength agent is preferably contained in an amount of 0.5% by weight or more, more preferably 0.6% by weight or more, and even more preferably 0.7% by weight or more, based on the solid content weight of the raw pulp. The upper limit of the amount added is preferably 7.0% by weight or less, more preferably 4.0% by weight or less, and even more preferably 2.0% by weight or less. If the content of the wet strength agent is less than 0.5% by weight, sufficient wet strength may not be exhibited. On the other hand, if the content of the wet strength agent exceeds 7.0% by weight, the paper strength improvement effect is hardly expected, resulting in high costs, poor texture, and dirt on the paper machine.
The amount of the wet strength agent can be quantified by elemental analysis such as the Kjeldahl method or energy dispersive X-ray analysis. In the present invention, the amount of the wet strength agent contained in the base paper refers to a converted value assuming that all of the nitrogen element quantified by the Kjeldahl method is derived from the polyamine epichlorohydrin resin.

The method for making the base paper is not particularly limited, and can be carried out using a papermaking machine such as a Fourdrinier papermaking machine including a top wire, an on-top former, a gap former, a cylinder papermaking machine, or a Yankee machine. The pH during papermaking may be acidic, neutral, or alkaline, but is preferably acidic. The papermaking speed is not particularly limited.
The method for drying the base paper is not particularly limited, but it is preferable to use a Yankee dryer for drying. The drying method is not particularly limited, and may be any known method such as a steam cylinder heating drying method, a hot air drying method, a gas type infrared drying method, or an electric type infrared drying method.

The basis weight of the base paper is not particularly limited, but is preferably 18 g/ ^m2 or more and 100 g/m2 or ^less in order to obtain an excellent balance between paper strength and handling. When the base paper of the present invention is used by wrapping it around a bottle or the like and folding it, the basis weight is preferably 18 g/m2 or ^more and 60 g/m2 ^or less. When the base paper is used in the form of small pieces, such as by attaching it to a bottle without folding it, the basis weight is preferably 50 g/m2 ^or more and 100 g/m2 ^or less.
The density of the base paper is, for example, preferably 0.5 g/cm ³ or more and 0.7 g/cm ³ or less, and may be 0.55 g/cm ³ or more and 0.70 g/cm ³ or less.

The base paper of the present invention is printed with product names, product information, etc. Printing can be done directly on the base paper, but printing can also be done after applying wax, wax, waterproof varnish, etc. Also, wax, wax, waterproof varnish, etc. can be applied after printing.

The present invention will be described in more detail below with specific examples, but the present invention is not limited thereto. In addition, unless otherwise specified, "parts" and "%" described below indicate "parts by weight" and "% by weight", respectively. In addition, unless otherwise specified in the present invention, numerical ranges are described as including their endpoints.

Measurement method: Basis weight: Measured in accordance with JIS P8124.
・Canadian Standard Freeness (CSF)
The measurement was performed in accordance with JIS P8121.
Bending resistance value was measured in accordance with JIS P8125-1:2017.

Tensile strength (wet)
The wet tensile strength was measured with an immersion time of 24 hours in accordance with the general method of JIS P8135: 1998. The measured wet tensile strength was divided by the basis weight measured above to calculate the wet tensile strength ratio.
(Drying)
The dry tensile strength and dry tensile strength index were measured in accordance with JIS P8113:1998.

"Example 1"
As the pulp raw material, 70 parts of softwood bleached kraft pulp (NBKP, CSF: 460 ml) and 30 parts of hardwood bleached kraft pulp (LBKP, CSF: 300 ml) were used. A stock was prepared by mixing 0.85% by weight (based on the dry weight of the pulp) of polyamine epichlorohydrin resin (WS4011, manufactured by Seiko PMC, wet strength agent), 0.3 parts of polyacrylamide (dry strength agent), aluminum sulfate, and a sizing agent with 100 parts of this mixed pulp. A wet paper was made from this stock using a papermaking machine and dried using a Yankee dryer to obtain a paper label base paper with a basis weight of 20 g/ ^m2 .

"Example 2"
A base paper for a paper label was obtained in the same manner as in Example 1, except that the basis weight was 26 g/ ^m2 .
"Example 3"
A base paper for a paper label was obtained in the same manner as in Example 1, except that the basis weight was 32 g/ ^m2 .
"Example 4"
A base paper for a paper label was obtained in the same manner as in Example 1, except that the basis weight was 37.9 g/ ^m2 .
"Example 5"
A base paper for a paper label was obtained in the same manner as in Example 1, except that the basis weight was 45 g/ ^m2 .

"Comparative Example 1"
As the pulp raw material, 20 parts of softwood bleached kraft pulp (NBKP, CSF: 450 ml) and 80 parts of hardwood bleached kraft pulp (LBKP, CSF: 510 ml) were used. A stock was prepared by mixing 1.40% by weight (based on the dry weight of the pulp) of polyamide polyamine-epichlorohydrin resin (AF255, manufactured by Arakawa Chemical, wet strength agent), 0.3 parts of polyacrylamide (dry strength agent), aluminum sulfate, and a sizing agent with 100 parts of this mixed pulp. A wet paper was made from this stock using a papermaking machine and dried to obtain a paper label base paper with a basis weight of 87.2 g/ ^m2 .

"Comparative Example 2"
As the pulp raw material, 13 parts of softwood bleached kraft pulp (NBKP, CSF: 620 ml) and 87 parts of hardwood bleached kraft pulp (LBKP, CSF: 440 ml) were used. A stock was prepared by mixing 0.25 parts of polyacrylamide (dry strength agent), cationic starch, filler, aluminum sulfate, and sizing agent with 100 parts of this mixed pulp. A wet paper was made from this stock using a papermaking machine and dried using a Yankee dryer to obtain a paper label base paper with a basis weight of 29.4 g/ ^m2 .

The base paper for paper labels obtained in Examples 1 to 5 of the present invention has excellent wet tensile strength ratio and is resistant to tearing even when wet, and is particularly suitable for paper labels for beverage bottles.

Claims (4)

A base paper for paper labels, characterized in that the wet specific tensile strength measured in accordance with the general method of JIS P8135:1998 with an immersion time of 24 hours is 10 kNm/kg or more in either the MD direction, the CD direction, or both. The base paper for paper labels according to claim 1, characterized in that the wet specific tensile strength measured in accordance with the general method of JIS P8135:1998 with an immersion time of 24 hours is 10 kNm/kg or more in both the MD and CD directions. 3. The paper label base paper according to claim 1, wherein the basis weight is from 18 g/ ^m2 to 100 g/ ^m2 . The base paper for paper labels according to any one of claims 1 to 3, characterized in that the bending resistance in the MD direction measured in accordance with JIS P8125-1:2017 is 3.0 mN or more and 50 mN or less.