JP2021165458A5 - - Google Patents

Description

The present invention relates to multi-layer paper and a method of making same.

Conventionally, as disposable tableware, medical instruments, and furniture, molded plastic resins have been widely used. In place of these conventional plastic resins, there are also bamboo and wooden ones, but they have the problem of high production costs and complicated production due to the necessity of molding. In addition, since plastic products pollute the ocean and affect the ecosystem of marine organisms, in recent years, from the viewpoint of environmental protection, the establishment of alternative technologies for plastic tableware, medical instruments, and furniture has been demanded.

On the other hand, in the prior art, paper-made stirring sticks and spoons with improved water resistance and hot water resistance have been proposed as alternative materials (see, for example, Patent Document 1). There have also been proposals for medical instruments made by folding a sheet of cardboard in multiple layers, and paper furniture made by stacking a plurality of cardboards (see, for example, Patent Documents 2 and 3).

Japanese Patent No. 4355283 Japanese Utility Model Laid-Open No. 59-102009 Registration No. 3220813

However, the conventional techniques described above are still insufficient in terms of the strength required for applications such as tableware, medical equipment, and furniture.
Therefore, in a form in which one sheet of thick paper is laminated to satisfy strength, etc., a lamination process is required, which not only causes an increase in cost, but also requires a synthetic material for laminating and laminating, so that it comes into direct contact with the human body. Not suitable for use.

SUMMARY OF THE INVENTION Accordingly, the main object of the present invention is to provide a multilayer paper exhibiting sufficient strength .

The multi-layer paper of the present invention, which solves the above problems,
Having a plurality of intermediate layers and a pair of surface layers formed on the front and back of the intermediate layer,
The pulp of the surface layer and the middle layer contains 80 % by mass or more of softwood kraft pulp and hardwood kraft pulp,
The mass ratio (%) of the softwood kraft pulp and the hardwood kraft pulp in the surface layer is 5/95 or more and 40/60 or less,
The mass ratio (%) of the softwood kraft pulp and the hardwood kraft pulp in the middle layer is 20/80 or more and 40/60 or less,
It is characterized by having a longitudinal tensile strength of 50.00 Mpa or more and a lateral tensile strength of 40.00 Mpa or more .

This multilayer paper has excellent strength properties . In addition, the object can be obtained from a single sheet of cardboard instead of a laminated structure, which is advantageous in terms of cost and productivity.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the multilayer paper which exhibits sufficient intensity |strength and a multilayer paper can be provided.

A multilayer paper according to one embodiment of the present invention will be described in detail below.
<Multilayer paper>
The multilayer paper has a plurality of middle layers and a pair of surface layers formed on the front and back sides of the middle layer. The middle layer is 3 to 7 layers.

Applications of this multi-layered paper include "tableware", "medical equipment", "furniture", and "stationery". "Tableware" is a broad concept that includes not only tableware such as plates, bowls, chopsticks, cups, coasters, trays, muddlers, spoons, forks, and paper containers, but also kitchen utensils such as knives and kitchen knives. "Medical instruments" include tongue depressors, ear picks, combs, pus basins, and other substitutes for current plastic medical instruments. "Furniture" can include hangers and other substitutes for current plastic furniture. "Stationery" includes substitutes for current plastic stationery such as clear boards, clips, and pens.

The pulp of the surface layer and the middle layer contains 80% or more of softwood kraft pulp and hardwood kraft pulp.
Preferably, it does not contain waste paper pulp. If the waste paper pulp is contained excessively, the strength is lowered, but if the upper limit is 20% by mass, the effect on the strength is small.

It is desirable to mix and blend softwood kraft pulp and hardwood kraft pulp. As a result, the thickness of the paper increases, and sufficient strength can be secured.
In addition, by setting the mass ratio (%) of the softwood kraft pulp and the hardwood kraft pulp in the surface layer to 5/95 or more and 40/60 or less, the hardwood kraft pulp is relatively rigid and easily densified. A pair of surface layers can obtain high density and rigid characteristics, and is excellent in strength. Furthermore, the surface layer can enhance the effect of suppressing permeation into the inside of moisture or oil components derived from the target object such as food.
On the other hand, by setting the mass ratio (%) of the softwood kraft pulp and the hardwood kraft pulp in the middle layer to 20/80 or more and 40/60 or less, the middle layer is good because it contains a large amount of flexible softwood kraft pulp. flexibility.

(Softwood kraft pulp, hardwood kraft pulp)
Here, the softwood kraft pulp is, for example, softwood unbleached kraft pulp (NUKP), softwood semi-bleached kraft pulp (NSBKP), or softwood bleached kraft pulp (NBKP).
Hardwood kraft pulp is, for example, hardwood unbleached kraft pulp (LUKP), hardwood semi-bleached kraft pulp (LSBKP), and hardwood bleached kraft pulp (LBKP). Among these, softwood bleached kraft pulp and hardwood bleached kraft pulp are preferably used from the viewpoint of achieving both the appearance and strength of the product after processing.

For each layer of the multi-layered paper, if necessary, chemical pulp such as hardwood sulfite pulp and softwood sulfite pulp can be used in appropriate combination.
When the multi-layered paper of the embodiment is used for paper tableware, for example, it comes into direct contact with an object such as food. Therefore, other pulps used in the multilayer paper are preferably chemical pulps, and more preferably ECF pulps, TCF pulps, and unbleached kraft pulps (UKP). ECF pulp is a chlorine-free bleached chemical pulp made without chlorine (Cl ₂ ) and bleached with chlorine dioxide (ClO ₂ ). TCF pulp is completely chlorine-free bleached chemical pulp produced by bleaching with oxygen (O), hydrogen peroxide (P), and ozone (Z) without using chlorine (Cl ₂ ). That is, since ECF pulp and TCF pulp contain very little or no chlorine ions, they have the advantage of being less likely to generate organic chlorine compounds such as dioxins even when incinerated at low temperatures. can be reduced. In addition, the use of unbleached kraft pulp makes it possible to mimic the color of wood, and by omitting the bleaching process, it is possible to reduce the environmental load by reducing energy consumption and _CO2 emissions.

The multi-layered paper of the embodiment has a multi-layered structure in which a pair of surface layers that are hard and hard to break and a middle layer that is flexible are combined. Can prevent bending.

(surface layer freeness)
In the multilayer paper of the embodiment, the lower limit of the Canadian Standard Freeness (CSF) of the pulp used for the surface layer is preferably 375 ml, particularly 410 ml. If the CSF of the pulp used for the surface layer is low, the drainage of the surface layer of the multi-layered paper may deteriorate during papermaking, resulting in difficulty in drying. As a result, it may lead to delamination of the surface layer. On the other hand, the upper limit of CSF of the pulp used for the surface layer is preferably 465 ml, particularly 450 ml. If the CSF is high, it becomes difficult to adjust the pulp fiber orientation in the paper machine, resulting in poor formation of the multi-layered paper, and there is a possibility that the strength and rigidity of the paper may be lowered when used as a paper container. The multi-layered paper is made by mixing bleached softwood kraft pulp and bleached hardwood kraft pulp with high freeness, thereby increasing the paper thickness and improving the stiffness. Here, Canadian Standard Freeness (CSF) is defined as disaggregated pulp by disaggregating in accordance with the pulp disaggregation method of JIS-P8220-1 (2012), and this disaggregated pulp is JIS-P8121-2 (2012) Canadian It is a value measured according to the standard freeness test method.

(middle class)
A plurality of intermediate layers are provided between the pair of surface layers. The middle layer is composed of softwood kraft pulp and hardwood kraft pulp. Further, the mass ratio (%) of the bleached softwood kraft pulp and the hardwood kraft pulp in the middle layer is 30/70 or more and 40/60 or less. By setting the mass ratio of the softwood kraft pulp to the hardwood kraft pulp in the middle layer within the above range, the middle layer has good flexibility because it contains a large amount of softwood kraft pulp. Therefore, as described above, the pair of surface layers which have rigidity and tend to break easily are combined with a flexible middle layer, so that the multi-layered paper is excellent in toughness and durability.

(middle layer freeness)
The lower limit of the Canadian Standard Freeness (CSF) of the pulp used for the middle layer of the multi-layered paper of the embodiment is preferably 460 ml, particularly preferably 470 ml. When the CSF is a low value, the dewaterability in the paper machine is poor. Furthermore, there is a possibility that the rigidity will be lowered. On the other hand, the upper limit of the CSF of the pulp used for the middle layer is preferably 550 ml, particularly 520 ml. If the CSF is excessively high, fibrillation is less likely to result in a decrease in strength and interlaminar strength. Furthermore, it is preferable that the Canadian standard freeness of the pulp used for the middle layer is higher than the Canadian standard freeness of the pulp used for the pair of surface layers from the viewpoint of maintaining the interlaminar strength of the middle layer and ensuring elastic force.

The total number of intermediate layers is preferably 3 or more, particularly 5 layers. When the total number of middle layers is 3 or more, the toughness and durability of the multilayer paper can be further improved. From the viewpoint of maintaining interlayer strength, the upper limit of the total number of the intermediate layers is preferably 7 layers or less.
3 to 7 layers are suitable for operation while maintaining interlaminar strength in the case of using a cylindrical multi-cylinder paper machine.

[Additive]
The multilayer paper preferably contains a sizing agent and a paper strength agent as papermaking additives in the surface layer and the middle layer.

(Sizing agent)
A sizing agent can be added to each layer of the multi-layered paper in order to further suppress penetration of moisture or oil derived from an object such as food into the interior. Examples of sizing agents include styrenic sizing agents, alkyl ketene dimers (AKD), alkenyl succinic anhydrides (ASA), neutral rosin sizing agents, rosin sizing agents, modified rosin emulsion sizing agents, and the like. Among these, rosin sizing agents and modified rosin emulsion sizing agents are preferred.

The rosin sizing agent is conventionally known in the papermaking field, and is not particularly limited. Rosin-based substances include, for example, reinforced rosins obtained by modifying rosins such as gum rosin, wood rosin and tall oil rosin with α,β-unsaturated carboxylic acids such as fumaric acid, maleic acid and acrylic acid or their anhydrides; Rosin esters obtained by reacting rosins with polyhydric alcohols such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol and diglycerin can be mentioned. In the present invention, the rosin-based sizing agent also includes those obtained by emulsifying these alone or a mixture thereof, and those obtained by emulsifying them alone and then mixing them. Furthermore, the emulsified product may contain various polymers added thereto in order to further improve the size development property.

The amount of the sizing agent added to the surface layer is preferably 0.5 kg/t or more and 5.0 kg/t or less in terms of solid content. The amount of the sizing agent added to the middle layer is preferably 2.0 kg/t or more and 5.0 kg/t or less in solid content. In addition, "kg/t" shows the mass (kg) per 1t of pulp. Water resistance can be improved by setting the amount of the sizing agent to be added within the above range.

(paper strength agent)
The multi-layered paper can have strength agent sizing added to each layer. By adding a paper strength agent, each layer can be given various strengths suitable for use as paper tableware.

Various known paper strength agents such as polyacrylamide resins, polyamide resins, polyamine resins, acrylic resins, melamine resins, urea resins, and polyamide epichlorohydrin resins can be used. Among these, amphoteric paper strength agents are preferably used. Examples of amphoteric polyacrylamides include copolymers of acrylamide with the above anionic monomers and cationic monomers, Mannich-modified copolymers of acrylamide with the above anionic monomers, Hoffmann decomposition products, and the like. According to the findings of the present inventors, amphoteric polyacrylamide is particularly preferable, and since amphoteric polyacrylamide has a self-fixing function, even if it is added to improve inter-paper strength, it does not become excessively cationic. , the modified rosin emulsion sizing agent can be stably fixed.

The amount of the paper strength agent added to each layer is preferably 12 kg/t or more and 30 kg/t or less in terms of solid content. By setting the addition amount of the paper strength agent within the above range, it is possible to impart various paper strengths such as interlaminar strength of multilayer paper. If the amount of the paper strength agent added is less than the above range, the interlaminar strength may not be sufficient. On the other hand, when the amount of the paper strength enhancer added exceeds the above range, the improvement in the interlaminar strength remains almost flat, and the yield of the added paper strength enhancer decreases, resulting in stains, foaming, etc. in the paper machine system. It may occur and the workability (deterioration of dehydration) may deteriorate. As a result, delamination may occur due to poor drying in the drying process.

(Other additives)
In addition, the multilayer paper may contain other various additives for papermaking within a range that does not impair the intended effects of the present invention. Other additives that can be added to the multilayer paper include, for example, known papermaking chemicals.

[Physical properties of multilayer paper]
(basis weight)
Basis weight is measured according to JIS-P8124 (2011). The basis weight of each layer of the multilayer paper does not need to be uniform, and the basis weights of the surface and middle layers are not particularly limited, but the basis weight of the surface layer is 75.0 g/m ² or more per layer. 260.0 g/m ² or less is preferable. Moreover, the basis weight of the entire middle layer is preferably 600 g/m ² or more and 950 g/m ² or less.

The lower limit of the basis weight of the multilayer paper as a whole is preferably 750 g/m ² and more preferably 860 g/m ² from the viewpoint of obtaining sufficient rigidity. The upper limit of the basis weight of the multilayer paper as a whole is preferably 1470 g/m ² , more preferably 1240 g/m ² . When the basis weight is high, sufficient rigidity can be easily obtained, but the thickness increases, and there is a possibility that folding creases are likely to occur with a calender roll during papermaking.

The ratio of the total basis weight of the pair of surface layers to the basis weight of the entire multilayer paper is preferably 25.0% or more and 35.0% or less. In the multi-layered paper comprising a pair of rigid surface layers and a flexible middle layer, by setting the ratio of the total basis weight of the pair of surface layers to the above range, it is possible to impart resistance to bending.

(paper thickness)
The paper thickness is measured according to “Paper and paperboard—Testing methods for thickness and density” described in JIS-P8118 (2014). The paper thickness of the multilayer paper is preferably 750 μm or more and 2,0200 μm or less. When the paper thickness of the multilayer paper is within the above range, peeling of the paper layers of the multilayer paper can be suppressed.

(density)
The density of the multilayer paper is preferably 0.65-1.00 g/cm ³ , particularly 0.73-0.85 g/cm ³ . When the density of the multi-layered paper is within the above range, contradictory performances such as high basis weight, excellent rigidity, and resistance to folding are exhibited. When the density of the multi-layered paper is less than 0.65 g/cm ³ , the multi-layered paper has a high flexural strength, but wrinkles during handling and delamination may easily occur. On the other hand, when the density of the multi-layered paper exceeds 1.00 g/cm ³ , wrinkles and delamination are unlikely to occur, but strength and rigidity may decrease. For example, the density of the multi-layered paper can be adjusted by the pulp freeness and ash content of the surface or middle layers and the calendering process.

(moisture)
The moisture content of the multilayer paper measured according to JIS-P8127 (2010) is preferably 9.0% or more and 11.0% or less. When the moisture content of the multi-layered paper is within the above range, the flexibility is improved, so that the workability in a folding machine and the effect of suppressing breakage of the folded portion when tableware is manufactured using the multi-layered paper can be improved.

(ash)
Ash content is measured according to JIS-P8251 (2003). The ash content of the multilayer paper is preferably 0.1% or more and 10.0% or less. When the ash content of the multi-layered paper is within the above range, the curl can be adjusted to be flat, and a decrease in interlaminar strength can be suppressed.

(Surface strength)
The surface strength was evaluated according to JAPAN TAPPI Paper Pulp Test Method No. Measured according to the "Surface Strength Test Method" by 1 m-72. The lower limit of the surface strength of the multilayer paper is preferably 10A. When the surface strength of the multi-layered paper is within the above range, it is possible to improve the abrasion resistance during peeling of the surface layer, transportation, and processing.

(Cobb size degree)
Cobb size degree is measured using distilled water at 23° C. in accordance with JIS-P8140 (1998). The upper limit of the Cobb sizing degree of the multilayer paper is preferably 50 g/m ² . If the bump sizing degree of the multi-layered paper is equal to or higher than the upper limit, the multi-layered paper may absorb moisture and cause waviness or wrinkles.

(Z-axis strength)
The Z-axis strength is measured according to JAPAN TAPPI Paper Pulp Test Method No. 18-1:2000, the Z-axis strength is preferably 380 kN/mm ² or more. By having the Z-axis strength, it is possible to suppress the occurrence of delamination and wrinkles during tableware molding.

(bending strength)
The bending strength is 10.0 N or more, so that when the tip is processed into a sharp tableware or the like,
No creases.

(tensile strength)
The tensile strength in the longitudinal direction is 50.00 MPa or more and the tensile strength in the lateral direction is 40.00 MPa or more, so that breakage and twisting do not occur when processed into furniture or the like that is subjected to a load for a long time.

(bending strength)
The bending strength in the vertical direction is 5.00 N or more and the bending strength in the horizontal direction is 3.00 N or more, so that cracks in the cross section do not occur when processed into tableware that requires deep engraving.

The multilayer paper is excellent in toughness and durability, and can be suitably used for paper tableware to replace conventional plastic tableware.

[Manufacturing method of multilayer paper]
The manufacturing method of multilayer paper is not particularly limited, but it can be manufactured, for example, by the following steps using a known multilayer paper machine.
(1) A slurry obtained by dispersing pulp fibers in water is mixed with an additive corresponding to each paper layer as necessary to prepare a stock for each paper layer.

(2) Next, using these raw material slurries, the surface layer, single layer or multi-layer middle layer and surface layer are combined in a paper machine in a neutral range so that the pH of the multi-layer paper becomes 6 or more and 8 or less. Make paper.
The paper-making method is not particularly limited, and known paper machines such as Fourdrinier, cylinder, hybrid former, gap former, etc. can be used, but particularly preferably cylinder and multi-cylinder papermaking. Using a paper machine, paper is made in multiple layers of 5 or more layers. In the papermaking process, a surface coating layer can be formed by applying a coating liquid to the surface of the surface layer using a coating device such as a size press, a rod metering size press, a gate roll coater, or the like.

(3) Next, it is pressed with pressure rolls to remove moisture.

(4) Next, it is dried with a dryer cylinder.
After drying, a calendering device such as a nip calender, a super calender, a machine calender, or a soft calender may be used for smoothing treatment. By performing a smoothing treatment, the multi-layered paper is given a high degree of gloss and can be suitably used for paper tableware having a high-class feel.

<Other embodiments>
The present invention is not limited to the above-described embodiments, and can be implemented in various modified and improved modes in addition to the above-described modes.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples.

Methods for measuring physical properties in Examples and Comparative Examples are as follows.
[Freeness (mL)]
The obtained multilayer paper is defiberized according to the pulp defiberization method of JIS-P8220-1 (2012) to obtain defiberized pulp, and the defiberized pulp is subjected to the Canadian standard freeness test of JIS-P8121-2 (2012). It was measured according to the method.

[Basis weight (g/m ² )]
It was measured in accordance with “Paper and paperboard—Basis weight measurement method” described in JIS-P8124 (2011).

[Paper thickness (μm)]
It was measured in accordance with "Paper and paperboard-Testing methods for thickness and density" described in JIS-P8118 (2014).

[Density (g/cm ³ )]
It was measured in accordance with "Paper and paperboard-Testing methods for thickness and density" described in JIS-P8118 (2014).

[Bending strength]
The bending strength was measured with a digital force gauge (manufactured by Imada Co., Ltd.) under the following test conditions. A test piece having a width of 15 mm and a length of 150 mm was fixed to a three-point bending jig, and the force gauge was lowered. The load at that time was taken as the bending strength (N). The test environment was set at a temperature of 26° C. and a humidity of 70%.

[Tensile strength]
Tensile strength is a value measured according to JIS-P-8113 (2006).

[Bending strength]
Bending strength was measured according to JIS K7171:2016. Specimens were prepared with a width of 15 mm and a length of 150 mm.

[Handling wrinkles]
The multi-layered paper thus obtained was wound around a paper tube (diameter of 9 inches), and wrinkles on the surface of the multi-layered paper were evaluated as follows. In addition, the range of wrinkles that can be used was judged to be an evaluation value of 3 or more.
5: No wrinkles during handling and no abnormalities in appearance.
4: There are small wrinkles in some parts, but there is no abnormality in the appearance.
3: There are wrinkles during handling, but the appearance is at a level that does not pose a problem.
2: There are wrinkles during handling, and there is a problem with the appearance.
1: Wrinkles are conspicuous on the entire surface, and the appearance is abnormal.

[Delamination]
The multi-layered paper thus obtained was wound around a paper tube (diameter of 9 inches), and delamination on the surface of the multi-layered paper was evaluated as follows. In addition, the range of delamination that can be used was judged to be an evaluation value of 3 or more.
5: No delamination and no abnormality in appearance.
4: There is thin delamination in part, but there is no abnormality in the appearance.
3: There is delamination, but the appearance is at a level where there is no problem.
2: There is delamination and there is a problem with the appearance.
1: Large delamination is conspicuous and the appearance is abnormal.

[Example 1]
(1) The composition of the surface layer and middle layer is shown below.
(surface)
Into 100 parts pulp slurry of 10:90 NBKP:LBKP of freeness 440 mL, the following ingredients were added.
Rosin emulsion-based sizing agent: solid content 0.8 kg/pulp t
Acrylamide-based paper strength agent: solid content 19.0 kg/pulp t
(middle class)
Into 100 parts pulp slurry of 35:65 NBKP:LBKP of freeness 440 mL, the following ingredients were added.
Modified rosin emulsion-based sizing agent: solid content 6.0 kg/pulp t
Acrylamide-based paper strength agent: solid content 19.0 kg/pulp t
(2) This pulp slurry was made into a seven-layer structure in total by using a multi-cylinder paper machine with a wire part consisting of a pair of surface layers and five intermediate layers. The basis weight of each layer is as shown in Tables 1 and 2.
(3) A coating liquid containing polyvinyl alcohol and paraffin wax was calender coated on the surface of the surface layer so that the following coating amount was applied to form a surface coating layer, and the multilayer paper of Example 1 was obtained. rice field.
Polyvinyl alcohol: 0.2 g/m ²
Paraffin wax: 0.2 g/m ²
Surface sizing agent: 0.6 g/m ²

[Examples 2 to 14, Comparative Examples 1 and 2 ]
Multilayered papers of Examples 2 to 14 and Comparative Examples 1 and 2 were prepared in the same manner as in Example 1, except that the types, contents, and physical properties of the raw materials were as shown in Tables 1 and 2. got
Comparative Example 2 is a multi-layered paper formed only from an intermediate layer.

The multilayer paper of the present invention can be suitably used for paper tableware, paper medical instruments, paper furniture, and paper stationery.

Claims (8)

Having a plurality of intermediate layers and a pair of surface layers formed on the front and back of the intermediate layer,
The pulp of the surface layer and the middle layer contains 80 % by mass or more of softwood kraft pulp and hardwood kraft pulp,
The mass ratio (%) of the softwood kraft pulp and the hardwood kraft pulp in the surface layer is 5/95 or more and 40/60 or less,
The mass ratio (%) of the softwood kraft pulp and the hardwood kraft pulp in the middle layer is 20/80 or more and 40/60 or less,
The tensile strength in the longitudinal direction is 50.00 Mpa or more, and the tensile strength in the transverse direction is 40.00 Mpa or more.
A multilayer paper characterized by: 2. The multilayer paper according to claim 1, wherein the mass ratio (%) of the softwood kraft pulp and the hardwood kraft pulp in the surface layer is larger than that of the surface layer. 2. The multi-layered paper according to claim 1, wherein said middle layer has 3 to 7 layers, and a pair of surface layers together has 5 to 9 layers. In the mass ratio (%) of the softwood kraft pulp and the hardwood kraft pulp in the surface layer, the mass ratio value of the middle layer is larger than the mass ratio value of the surface layer,
The middle layer has 3 to 7 layers, and a pair of surface layers together has 5 to 9 layers,
Multilayer paper according to claim 1. 2. The multi-layer paper according to claim 1, which has a bending strength of 10.0 N or more. 2. The multi-layered paper according to claim 1, having a vertical bending strength of 5.00 N or more and a horizontal bending strength of 3.00 N or more. The density of multilayer paper is 0.65-1.00g/cm ³ The multi-layered paper of claim 1, wherein: Tableware, medical equipment, furniture, and stationery formed from the multi-layered paper of claim 1.