JP2003155700A - Base paper for acidic food cup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide base paper for acidic food cups which is used for acidic food cups capable of preventing the penetration of a liquid from the cross section of the base paper, when the cups are charged with the acidic food. SOLUTION: This base paper for acidic food cups is characterized in that a weight increase rate is <10 wt.%, when a square test piece having a side length of 4.0 cm and formed by adhering 20 μm-thick polyester adhesive films to both the sides of the cup base paper is immersed in an organic acid aqueous solution adjusted to pH 4 at 40 deg.C. The acidic food paper cup is made from the acidic food cup base paper. The cup base paper is preferably produced by making single layer paper from pulp having a freeness of CSF350 ml to CSF500 ml as a raw material in the presence of a specific alkylketene dimmer as an inner sizing agent by the use of a long net paper machine.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base paper for acidic foods used for beverage paper cups, containers for yogurt, containers for ice cream, etc., particularly acidic foods suitable for manufacturing and filling acidic foods such as yogurt. It relates to the base paper for cups.

[0002]

2. Description of the Related Art In cup base paper, a polyethylene is laminated on a paper base material to prevent permeation of liquid from the surface. The paper cup is made by punching a cup base paper (polylaminated paper) laminated with polyethylene into a fan shape, which is the expanded shape of the cup, and heat-sealing both ends of the straight part of the fan shape to form a cup shape. It is manufactured by a series of operations in which a bottom paper is inserted and heat-sealed, and then, a circumferential portion of an upper end is wound outside, a top curl process (a process of forming a portion to be a base of a cup), and a seamer process.

The paper cup manufactured by the above method is provided with water resistance and oil resistance by the polyethylene laminate. However, since the cross-section of the base paper is exposed to the liquid with which the cup is filled, the portions where both ends of the fan shape are heat-sealed to each other may cause a defect that the liquid penetrates into the base paper.

[0004] With the cup base paper for general beverages as disclosed in JP-A-6-101190, a paper cup with a usage time of about 1 hour can be used, but in a food packaging material application such as a yogurt cup. , The period from filling to consumption is longer than one week, so it cannot be handled.

Yogurt, in particular, may undergo fermentation in a container and may be kept at a relatively high temperature of 30 to 40 ° C. for 2 to 4 hours. When exposed to an acidic solution under such conditions, penetration of the solution from the cross section of the base paper is promoted, which may cause serious defects such as bleeding.

In the paper cup in such a field, Japanese Patent Laid-Open No. 55-164143 discloses that a side edge of a paper cup blank is slid down to form an inclined surface, and the inclined surface is formed by bending the film cup on one side to the other surface. Although a method of preventing liquid leakage by winding it up and molding it so as to face the inside of the paper cup body is disclosed, it has the drawback of complicating the processing steps.

Therefore, a base paper for a paper cup suitable for filling an acidic food using a general paper cup manufacturing method has not been found yet.

[0008]

DISCLOSURE OF THE INVENTION The present invention satisfies the polyethylene laminating suitability, printability, molding suitability and food safety required for food paper container base paper, and is filled with an acidic food represented by yogurt. In addition, the present invention provides an acidic food paper cup which is capable of suppressing permeation of the acidic aqueous solution from the cross section of the base paper, in other words, having high cross-sectional permeation resistance.

Further, as compared with the single-layer papermaking, the multi-layer papermaking can use a raw material that has been beaten, so that a dense paper layer structure can be obtained, which is advantageous for cross-section penetration. However, in the case of multi-layer papermaking, the strength between the paper layers is weak, so that there is a drawback that the layers are separated during the molding process.
Therefore, in the present invention, the second goal is to achieve the above target cross-sectional penetration resistance with single-layer papermaking.

[0010]

[Means for Solving the Problems] As a result of intensive investigations by the present inventors, a method for evaluating cross-sectional permeation resistance of a cup base paper for acidic food used in a paper container filled with acidic food that is assumed to undergo lactic acid fermentation has been investigated. A polyester adhesive film with a thickness of 20 μm is attached to both sides of the base paper, and the length of one side is 4.0 cm.
The square test piece of was used as a standard solution of an organic acid aqueous solution adjusted to pH 4 corresponding to acidic food, and the weight increase rate when immersed for 2 hours at 40 ° C corresponding to the fermentation temperature for yogurt production It was found that it can be evaluated.
If the weight increase rate of the test piece at this time is less than 10% by weight,
It was found that the above problems can be solved. Such cup base paper has, for example, freeness CSF of 350 ml or more and CSF5
It is obtained by making a single-layer paper with a Fourdrinier paper machine using pulp of less than 00 ml as a raw material and a specific alkyl ketene dimer as a sizing agent.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The method for evaluating cross-sectional penetration resistance of the present invention will be described in detail below. 20μ thickness on cup base paper
What stuck the polyester adhesive film of m on both sides was used as a test piece. The shape of the test piece is a square having a side of 4.0 cm corresponding to the length of the heat-sealed portion of the food cup. If the water permeation distance of the heat-seal-bonded part exceeds 2.0 mm, it will be a serious subject of claims, so the original goal of cross-sectional permeation resistance in the above test is
The permeation distance of the standard solution is less than 2.0 mm. However, since the permeation distance is partially variable and it is difficult to objectively evaluate it, the cross-section of the present invention is equivalent to the permeation distance of the standard solution into the test piece from the weight change of the test piece due to the permeation of the standard solution. The target value of permeability is set. That is, assuming that the density of the base paper is 0.75 g / cm ³ and the swelling ratio of the base paper during water penetration is 20%, the permissible range of the standard solution is 2.
In order to make it less than 0 mm, the target is achieved by setting the weight increase rate due to the permeation of the standard solution to less than 10.0% by weight. In addition, as a measurement condition, the test piece is immersed for 2 hours under the condition of 40 ° C. corresponding to the fermentation temperature for producing yogurt, and the weight increase rate is measured.

The standard solution has a pH equivalent to that of acidic foods.
Use an organic acid aqueous solution with a concentration of 1 wt% adjusted to 4. As the organic acid, it is preferable to use an organic acid contained in acidic food such as citric acid, lactic acid, acetic acid, succinic acid, malic acid.

The cup base paper for acidic foods of the present invention is produced by wet-making paper pulp with wood pulp as a main component containing a sizing agent, a wet strength enhancer and the like. Pulp used in the present invention, softwood kraft pulp, hardwood kraft pulp, chemical pulp such as sulfite pulp, stone grind pulp, mechanical pulp such as thermomechanical pulp, kenaf, bamboo, non-wood fibers obtained from hemp, etc. And the like can be appropriately mixed.

To complete the invention, it is necessary to prevent the permeation of acidic liquids. In order to suppress the permeation of the liquid, it is effective to take measures such as reducing the permeable pore diameter, reducing the continuous pore volume, and increasing the water repellency of the paper substrate.

Regarding the reduction of the pore diameter and the reduction of the continuous pore volume, the freeness of the raw pulp is a major controlling factor. Freeness of raw pulp is CSF 350m
It is preferably 1 or more and less than CSF 500 ml. When the freeness of the pulp is CSF 500 ml or more, the paper layer structure becomes rough, so that the cross-sectional penetration resistance targeted by the present invention cannot be obtained. Cross-penetration resistance improves as the beating progresses, but the paperboard base paper requires a high basis weight of 200 g / m ² or more. Therefore, if the CSF is less than 350 ml, single-layer papermaking is difficult. Further, if a plurality of raw material pulps are used and the mixed freeness thereof is CSF 350 ml or more and less than CSF 500 ml, C
It is also possible to appropriately mix pulp with SF less than 350 ml and pulp with CSF 500 ml or more.

The phenomenon that swelling is caused by breaking the interfiber bond between pulps and the pore diameter is enlarged during the permeation of the liquid is an important controlling factor in controlling the cross-sectional penetration resistance. As a specific method of suppressing swelling, a method of suppressing swelling of the base paper due to water absorption by adding a wet paper strength enhancer represented by polyamide epichlorohydrin resin is also effective. The wet strength agent is preferably contained in the range of 0.1% by weight or more and 0.5% by weight or less based on the absolute dry weight of pulp.

Regarding the water repellency of the base paper for acidic foods of the present invention, the selection of the internally added sizing agent is a major controlling factor. As the internally added sizing agent, it is desirable to use an alkyl ketene dimer having an alkyl group having a carbon chain length of C18 or more as represented by the following general formula 1. Even when rosin size is used, it is possible to obtain a high sizing property with a Stekihide sizing degree of 600 seconds or more, but since the sizing property will decrease under low pH conditions, it will be less than the acidic aqueous solution of the present invention. Not suitable because the size effect is small. on the other hand,
Since the alkyl ketene dimer exhibits sufficient water repellency even under a low pH condition, it can be expected to have a high sizing property for an acidic aqueous solution, which is the object of the present invention.

[0018]

[Chemical 2] (However, R ₁ and R ₂ are linear or branched alkyl groups having 18 or more carbon atoms.) The size effect of the alkyl ketene dimer depends on the alkyl group R
₁ and R ₂ , the size effect increases as the number of carbon atoms in each increases, and both are linear or branched alkyl groups having 18 or more carbon atoms, which are resistant to the acidic aqueous solution of the present invention. It became clear that cross-sectional permeability can be easily obtained. Further, if either _one of R ₁ and R _{2 has} a carbon number of less than 18, it is difficult to obtain the cross-sectional penetration resistance targeted by the present invention.

The addition amount of the alkyl ketene dimer is preferably 0.15% by weight or more and 0.75% by weight or less per pulp. The larger the amount added, the better the cross-section penetration resistance, but even if 0.75 wt% or more is added, the improvement in size is leveled off and is economically meaningless.

A styrene / maleic acid type copolymer, a styrene / acrylic acid type copolymer, an alkenyl succinic anhydride, an alkyl ketene is applied to the base paper obtained by these methods by using a size press coater, a calendar size press or the like. It is desirable to apply or impregnate a surface sizing agent such as dimer in order to improve cross-sectional penetration resistance. In particular, it is preferable to use a styrene / maleic acid type copolymer or a styrene / acrylic acid type copolymer. The application amount of the surface sizing agent is 0.1 g / m ² or more per surface and 1.0 g / m ²
The following range is preferable.

[0021]

[Examples] The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In the examples,% is% by weight, x / y is x
Indicates the weight ratio of y.

The rate of increase in weight when immersed in an aqueous citric acid solution was measured by the following method. The basis weight of the paper substrate is measured, and both sides of the paper substrate are laminated with a 20 μm thick polyester adhesive film. Laminated paper 40 mm on a side
Cut into squares to make sample pieces. After measuring the weight of the test piece, the sample piece is immersed in a 1.0% concentration aqueous citric acid solution adjusted to pH 4 at 40 ° C. for 2 hours. After the immersion, the solution adhering to the surface is thoroughly wiped off, and then the weight of the test piece is measured. Based on these measurement results, the weight increase rate was calculated from the following formula. Weight increase rate = {(weight of sample after immersion-weight of sample before immersion) / weight of paper base material in sample} × 100

[Example 1] Hardwood kraft pulp (LB
KP) and softwood kraft pulp (NBKP) were blended at a weight ratio of 85/15 to beat pulp to CSF 400 ml to obtain raw pulp. Alkyl ketene dimer in which the number of carbon atoms of the alkyl group is 18 is used as the raw pulp
0.35%, polyamide epichlorohydrin resin (trade name: WS570, manufactured by Japan PMC Co., Ltd.) 0.2% to pulp, cationized starch (trade name: Neotac 130, manufactured by Nippon Food Processing Co., Ltd.) 0.5% added to pulp After that, the pH was adjusted to 7.5 with sodium carbonate to obtain a raw material slurry. This raw material was paper-made by a Ford Linear Fourdrinier paper machine. Then, the obtained paper web was subjected to a calendar size press, using polyvinyl alcohol (trade name: Gohsesize P700, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) and styrene-maleic acid (trade name: PM).
351, manufactured by Arakawa Chemical Industry Co., Ltd.) was applied at a surface size aqueous solution of 5.0 / 2.5 in a weight ratio of 0.5 g / m ² per side to prepare a paperboard base paper having a basis weight of 300 g / m ^2. Obtained. The weight gain of this base paper after being dipped in a citric acid aqueous solution for 2 hours was 7.5%.

[Example 2] Hardwood kraft pulp (LB
KP) and softwood kraft pulp (NBKP) were blended in a ratio of 85/15 to beat CSF to 450 ml to obtain a raw material pulp. 0.60% of pulp to alkyl ketene dimer with 18 carbon atoms in the alkyl group
Polyamide epichlorohydrin resin (trade name: WS57
0, Japan PMC Co., Ltd. 0.2% against pulp, cationized starch (trade name: Neotac 130, Nippon Food Processing Co., Ltd.)
After adding 0.5% to pulp, pH 7.5 with sodium carbonate
Was adjusted to a raw material slurry. This raw material was paper-made by a Ford Linear Fourdrinier paper machine. Then, the obtained paper web was subjected to a calendar size press to obtain polyvinyl alcohol (trade name: Gohsesize P700, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.).
And styrene-maleic acid (trade name: PM351, manufactured by Arakawa Chemical Industry Co., Ltd.) at a weight ratio of 5.0 / 2.5, and the surface size aqueous solution is coated at 0.5 g / m ² per side. A paper container base paper having a basis weight of 300 g / m ² was obtained. The weight gain of this base paper after being dipped in an aqueous citric acid solution for 2 hours was 5.0%.

[Comparative Example 1] Hardwood kraft pulp (LB
KP) and softwood kraft pulp (NBKP) were blended at a weight ratio of 85/15 to beat CSF to 550 ml to obtain a raw material pulp. Alkyl ketene dimer in which the number of carbon atoms of the alkyl group is 18 is used as the raw pulp
0.60%, polyamide epichlorohydrin resin (trade name: WS570, manufactured by Japan PMC Co., Ltd.) 0.2% to pulp, cationized starch (trade name: Neotac 130, manufactured by Nippon Food Processing Co., Ltd.) 0.5% added to pulp After that, the pH was adjusted to 7.5 with sodium carbonate to obtain a raw material slurry. This raw material was paper-made by a Ford Linear Fourdrinier paper machine. Then, the obtained paper web was subjected to a calendar size press, using polyvinyl alcohol (trade name: Gohsesize P700, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) and styrene-maleic acid (trade name: PM3).
51, Arakawa Chemical Industries Co., Ltd.) was mixed at a weight ratio of 5.0 / 2.5 to apply a surface size aqueous solution to 0.5 g / m ² per side, and a paper base paper with a basis weight of 300 g / m ² was applied. Obtained.
The rate of weight increase of this base paper after being immersed in a citric acid aqueous solution for 2 hours was 12.5%.

[Comparative Example 2] Hardwood kraft pulp (LB
KP) and softwood kraft pulp (NBKP) to 85/15
Beat pulp containing blended CSF up to 400 ml
I thought Any carbon number of alkyl group in raw pulp
0.60% to pulp with an alkyl ketene dimer of 16
Polyamide epichlorohydrin resin (trade name: WS570,
0.2% pulp from Japan PMC Co., Ltd., cationized starch
Powder (brand name: Neotac 130, manufactured by Nippon Food Processing Co., Ltd.)
After adding 0.5% to pulp, adjust the pH to 7.5 with sodium carbonate
The raw material slurry was adjusted. Fordlini
Paper was made using a fourdrinier paper machine. Then, the obtained
With a render size press, polyvinyl alcohol
(Product name: Gohseize P700, Nippon Synthetic Chemical Industry Co., Ltd.
Made) and styrene-maleic acid (trade name: PM351, Arakawa Chemical)
Surface syrup containing 5.0 / 2.5 weight ratio of Kogyo Co., Ltd.
0.5 g / m per one side of aqueous solution^TwoCoated so that
The basis weight is 300g / m ^TwoI got the paper container base paper. This base paper
After being immersed in an aqueous solution of enoic acid for 2 hours, the rate of weight increase is 16.5%.
Met.

[Comparative Example 3] Hardwood kraft pulp (LB
KP) and softwood kraft pulp (NBKP) were blended at a weight ratio of 85/15 to beat pulp to CSF 400 ml to obtain raw pulp. Alkyl ketene dimer in which the number of carbon atoms of the alkyl group is 18 is used as the raw pulp
0.15%, polyamide epichlorohydrin resin (trade name: WS570, manufactured by Japan PMC Co., Ltd.) 0.2% to pulp, cationized starch (trade name: Neotac 130, manufactured by Nippon Food Processing Co., Ltd.) 0.5% added to pulp After that, the pH was adjusted to 7.5 with sodium carbonate to obtain a raw material slurry. This raw material was paper-made by a Ford Linear Fourdrinier paper machine. Then, the obtained paper web was subjected to a calendar size press, using polyvinyl alcohol (trade name: Gohsesize P700, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) and styrene-maleic acid (trade name: PM3).
51, Arakawa Chemical Industries Co., Ltd.) was mixed at a weight ratio of 5.0 / 2.5 to apply a surface size aqueous solution to 0.5 g / m ² per side, and a paper base paper with a basis weight of 300 g / m ² was applied. Obtained.
The rate of increase in weight of the base paper after being immersed in the citric acid aqueous solution for 2 hours was 18.0%.

Each base paper obtained by the above method has a thickness of 20 μm.
m polyethylene laminated, punched into a fan shape and a circular shape, and heat-sealed into a cup shape to obtain a container having a capacity of 120 ml. 100 pasteurized raw milk in this cup
After injecting ml and sugar 5g, and further inoculating lactic acid bacteria,
It was sealed with a polyethylene film and kept at 38 ° C. for 4 hours to prepare yogurt having a pH of 4.4.

The containers formed by using the base papers manufactured by the methods of Examples 1 and 2 were good with no whey penetrating from the heat-sealed joints of the containers even after the yogurt was manufactured. On the other hand, the container formed by using the base paper produced by the method of Comparative Examples 1 to 3 is, after producing yogurt,
The whey was significantly penetrated from the heat-sealed joint portion of the container to the base paper layer, and was not suitable as a food container.

[0030]

INDUSTRIAL APPLICABILITY The cup base paper of the present invention can effectively prevent liquid permeation from the cross section of the paper due to acidic foods represented by yogurt by suppressing the permeability to a 1% citric acid aqueous solution. As a result, an acidic food paper cup can be provided by a simple can-making method similar to a beverage paper cup. Therefore, the industrial significance of the present invention is great.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4L055 AA02 AA03 AC06 AG40 AG63                       AG64 AG70 AG71 AG82 AG89                       AH12 AH13 AH50 AJ02 AJ03                       BB03 BE14 DA01 EA05 EA10                       EA32 FA17 FA19 FA30 GA05                       GA50

Claims (4)

[Claims] 1. A cup base paper having a thickness of 20 μm and a polyester adhesive film laminated on both sides, and one side having a length of 4.0 cm.
A cup raw paper for acidic foods, in which the weight increase rate is less than 10% by weight when the square shaped test piece is immersed in an organic acid aqueous solution adjusted to 40 ° C. and pH 4 for 2 hours. 2. The cup base paper for acidic foods according to claim 1, wherein the raw pulp has a freeness of CSF of 350 ml or more and less than 500 ml of CSF and is produced by single-layer paper making with a Fourdrinier paper machine. 3. An internal sizing agent represented by the following general formula (1):
The alkyl ketene dimer represented by the formula (1) is contained in an amount of 0.20% by weight or more and less than 0.75% by weight based on the weight of the dry pulp.
The cup base paper for acidic foods according to claim 2. [Chemical 1] (However, R ₁ and R ₂ are linear or branched alkyl groups having 18 or more carbon atoms) 4. The base paper for acidic food cups according to claim 1, wherein a styrene / maleic acid copolymer or a styrene / acrylic acid copolymer is applied or impregnated as a surface sizing agent.