JP2000170096A - Low density foamed paper and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new production method of a foamed paper having low density, excellent in heat-insulating properties, cushioning properties, etc., capable of greatly decreasing the consumption of thermal energy compared with conventional production methods, and hardly causing the generation of dioxin when the low density foamed paper of the product is subjected to the incineration treatment by compounding a blowing agent with a pulp slurry, and further to obtain the product. SOLUTION: This method for heating and foaming the paper web obtained by compounding expandable particles with the pulp and subjecting the obtained pulp with the expandable particles to the paper-making to provide the objective low-density bulky paper comprises selecting microcapsules obtained by using an acrylonitrile-based thermoplastic resin as the outside shells of the capsules as a heat-blowing agent added to the pulp, dispersing the capsules so that the capsules passing 100 mesh may occupy 98% or more of the capsules to uniformly disperse the capsules in the pulp slurry, forming the wet paper web, and heating and foaming the wet paper web while regulating the amount of moisture of the wet paper web before the heating and foaming so as to be in the state of 41-60%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to heat insulation, moisture retention,
The present invention relates to a low-density foamed paper having excellent cushioning properties and a method for producing the same, and more particularly to a low-density foamed paper which does not exhibit avatar-like fine protrusions due to uneven dispersion of a heating foaming agent or aggregation of the foaming agent, and a method for producing the same. Things.

[0002]

2. Description of the Related Art Conventionally, as a sheet used for food containers and packaging materials, plastic foams such as polyethylene and polystyrene have excellent heat insulating properties, heat insulating properties and cushioning properties, as well as good moldability and workability. It was used in large quantities because it was cheap. However, in recent years, there has been a shift to natural pulp-based paper substrates, which do not pollute the environment, are naturally decomposed, damage incinerators even when waste is incinerated, and are less likely to generate pollutants and smoke. I'm under pressure.
As a means for imparting these heat insulating functions to a paper base material, there is known a method in which a foaming agent exhibiting heat insulating performance is mixed together with pulp and foamed on a heating roll (dryer) of a paper making machine. Japanese Patent No. 2689797).

[0003] In addition to the above, the water content of paper 5 obtained by blending foamable microcapsules with a raw material mainly composed of pulp for papermaking.
JP-A-8-226097 discloses a method for producing a low-density paper by superposing and impregnating an impregnating liquid mainly composed of a rubber latex or a synthetic resin emulsion on a surface of a wet paper of 0 to 60% by weight and then heating and foaming the impregnating liquid. Is disclosed.

[0004] In the former method, a wet paper sheet (hereinafter referred to as a wet paper sheet) obtained by blending foamable particles that function as a foaming agent with pulp and making the paper.
When the low-density paper is produced by foaming by heating to obtain a low-density paper, the moisture content of the web before heating and foaming is 65 to 72%. If it is less than 65%, uneven foaming occurs, and it is necessary to heat while maintaining in the above-mentioned moisture range on the knowledge that uniform foamed paper cannot be obtained.

[0005] Even in the latter case, as described above, the web surface after press dewatering is wet impregnated with the emulsion liquid or the like, so that the water content in the web before impregnation is in the range of 50 to 60% by weight. However, the water content before heating and foaming becomes a high value of 62 to 69% (converted value based on the numerical value described in the above-mentioned publication), and as a result, the following problems could not be solved. .

That is, in the prior art,
Although it is disclosed that when papermaking is performed by mixing foaming agent particles in a pulp fiber-based stock, a paper having a much lower density can be produced as compared with a conventional low-density foamed paper. No solution has been suggested for the problem of the appearance of avatar-shaped fine projections caused by dispersion unevenness and aggregation caused by the dispersion of the foaming agent particles and foaming unevenness due to the dryer surface temperature.

Further, since a high water content is retained in the web before heating and foaming, the drying efficiency is low, and not only does the energy unit greatly increase compared to ordinary paper, but also the existing paper machine is used. Usually, the drying ability of the paper machine is fixed, so that the web is dried to a predetermined moisture content (usually 5 to 8%). There was a problem that productivity had to be low due to extremely slow response.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lower density of 0.2 g / m ³ or less than polystyrene foam,
An object of the present invention is to provide a low-density foamed paper having excellent heat insulating properties, heat retaining properties and cushioning properties, and having no avatar-shaped fine protrusions in a paper layer and on a paper surface. Further, in the present invention, in obtaining the low-density foamed paper, the dispersion of the foaming agent particles is sieved to prevent uneven dispersion and aggregation, and to reduce the water content before heating and foaming to 41 to 60%. After that, by drying at a dryer temperature of 120 to 150 ° C., the basic unit of heat energy required for drying can be greatly reduced.

[0009]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors heat-foam a paper web formed by mixing a pulp with a foaming agent to produce a bulky low-density foamed paper. In the method, a heat-expandable microcapsule is used as a heating foaming agent to be added to the pulp,
As a particle diameter of the heating foaming agent in the pulp slurry of the heating foaming agent, at least 100 mesh passes for 9
After being dispersed so as to account for 8% or more, the slurry is dried on a dryer of a paper machine. At this time, if the wet web web is heated and foamed while keeping the moisture content of the wet paper web before heating and foaming in the range of 41 to 60%, there is no avatar-like fine projections, and stable operability and high quality are obtained. Product was obtained. That is, the present invention includes the following inventions.

(1) A method for producing a low-density, bulky paper by foaming a paper web formed by mixing a pulp with a heating foaming agent by heating, wherein the heat expansion is performed as a heating foaming agent to be added to the pulp. While using the microcapsules, the capsules are uniformly dispersed in the pulp slurry,
At this time, at least 100 mesh passes for the blowing agent in the pulp slurry of the blowing agent had a particle size of 98.
%, After dispersing the pulp slurry so as to occupy the pulp slurry, and then subjecting the pulp slurry to heat foaming.

(2) After the pulp slurry described in (1) above is formed, it is heated and foamed while keeping the moisture content of the wet paper web before heating and foaming at least in the range of 41 to 60%. A method for producing low-density foamed paper.

(3) The method for producing a low-density foamed paper according to the above (2), wherein a surfactant is used in combination to uniformly disperse the heating foaming agent in the pulp slurry.

(4) The heating foaming agent is added to the pulp slurry at a solid content of 5 to 20% based on the weight of the pulp, and then uniformly dispersed to form a wet paper web. After making the water content of the web 41 to 60%, the web is heated and foamed through a dryer,
The method for producing a low-density foamed paper according to the above (2) or (3), wherein a low-density paper sheet is obtained.

(5) As a heating foaming agent, a microcapsule using an acrylonitrile-based thermoplastic resin for the capsule shell is selected, and when the capsule is dispersed in a pulp slurry, a polycarboxylic acid type polymer is used. Wherein the anionic surfactant is used as a dispersant and added in an amount of 0.3 to 0.8% based on the solid content of the expandable particles. A method for producing low-density foamed paper.

(6) After passing the microcapsules as the heating foaming agent through a strainer or screen having a sieve of 100 to 150 mesh, the capsules are added to a pulp slurry, mixed uniformly, and heated and foamed. A method for producing a low-density foamed paper, which comprises subjecting a wet paper web to a water content of 41 to 60% before heating and foaming.

(7) A low-density foamed paper produced by the method according to any one of (1) to (6).

In the present invention, an aqueous dispersion of a foaming agent is mixed with a pulp slurry through a strainer or a dispersant, and then the slurry is formed into a sheet by a paper machine and then pressed. Dehydrate in part. The method also includes a method in which the wet paper web after dehydration is dried and heated and foamed in a subsequent dry part to fix the foamed state to produce a low-density foamed paper.

"Avatar-shaped fine projections" due to uneven foaming occurring on the low-density foamed paper layer or the low-density foamed paper surface that poses a problem
Is the unevenness of the microscopic temperature distribution during drying,
It has been found that this is caused by two phenomena, that is, non-uniform dispersion of the foaming agent (hereinafter, both are collectively referred to as dispersion unevenness). The unevenness of the microscopic temperature distribution in the drying described above is caused by uneven contact between the web and the dryer surface (there is a portion that is not in contact), resulting in uneven drying and temperature rise. In the form of "fine projections". In the production of general paper, it is known that the press pressure of a dewatering press roll of a wet paper web and the pressure of a touch roll pressed against a dryer affect the density of paper. In producing low-density foamed paper, if the pressure of the touch roll is lowered, the contact between the web and the dryer becomes uneven, and the above-mentioned “abata-shaped fine projections”
Occurs. In the present invention, it has been found that the touch pressure of the touch roll may be set to the same level as that of ordinary papermaking in the production of low-density foamed paper, whereby unevenness of the temperature distribution can be prevented.

On the other hand, the non-uniform dispersion of the foaming agent (dispersion unevenness) described above includes, when the foaming agent is added to the pulp slurry, a case where the foaming agent particles are agglomerated and aggregated, There are two cases where the paper is made in a state where the slurry and the foaming agent are not uniformly dispersed. In the latter case, there is no problem if chemical additive technology in ordinary papermaking is utilized. The main cause is considered to be the former, and the particle diameter of the foaming agent particles before foaming is 10 to several tens of microns (μm).
The capsule contains a low boiling point hydrocarbon. When a temperature higher than the softening point of the resin forming the outer shell of the capsule is applied to the capsule, foaming occurs and the volume expands 30 to 150 times (3 to 5 times in diameter) before foaming. If there is a portion where a plurality of foaming agent particles are aggregated into a mass in the web, the portion expands more in volume in the heating and drying process than the other portions, and becomes the above-mentioned “abata-shaped fine projections”. To prevent this, 100 to 15
The aqueous dispersion of the foaming agent described above may be passed through a strainer formed by a 0-mesh wire net or the like to remove aggregates larger than the sieves of the strainer.

In the drying of paper, when the web is dried to a water content of 30% or less by a drier, hydrogen bonding between the cellulose fibers acts, and the bonding between pulp fibers starts gradually. This binding occurs rapidly from a water content of about 15% and hinders foaming of the foaming agent. Considering the phenomenon in the thickness direction of the paper, a sharp decrease in moisture and temperature rise occur near the surface of the paper that is in contact with the dryer surface. Coupling will occur. In addition, when the foaming agent foams, the part becomes a heat insulating layer by the gas of the contained hydrocarbon, so when trying to produce low-density foamed paper of a certain U.S.P. or more, the back layer further away from the dryer surface is In addition, since drying and foaming require time, drying from one direction is inefficient, and it is necessary to reduce the speed of paper making. Therefore, in this case, low-density foamed paper can be efficiently produced by alternately drying the front and back sides using a dryer having two or more stages.

The pulp used in the present invention includes, for example, wood pulp such as chemical pulp of hardwood and hardwood, mechanical pulp, non-wood natural pulp such as hemp and cotton, and synthetic chemistry used in ordinary papermaking. Pulp, and synthetic fibers such as polyether and rayon, etc. may be mentioned. However, the foaming agent foams in the gaps between the fibers and causes the density (thickness) of the resulting paper to decrease. Therefore, even if hemp, synthetic fiber, or the like, which tends to have a low density, it is not expected that the density will be much lower than that of wood pulp.

The heating foaming agent used in the present invention may be of any type as long as it is a heat-expandable microcapsule in which a low boiling point solvent is encapsulated in a microcapsule.
Thermoplastic resin such as polyacrylonitrile or acrylonitrile-alkyl methacrylate copolymer, which is a non-chlorine compound, produces dioxin even when used low-density foamed paper is incinerated. It is environmentally preferable because there is no fear of causing the above. For example,
It is a commercially available product generally called a heat-expandable microcapsule, and is referred to as Expancel 053WU (hereinafter # 053WU).
), An outer shell of a capsule is formed of an acrylonitrile / alkyl methacrylate copolymer, and the outer shell starts to soften at around 95 ° C. The capsule contains a hydrocarbon (isobutane) having a low boiling point, and the volume rapidly expands (foams) due to the internal pressure of gasified isobutane as the outer shell resin softens. The expansion ratio of the blowing agent particles alone reaches a maximum around 143 ° C., and at a temperature higher than 143 ° C., the internal pressure of isobutane becomes too high, so that the softened capsule is gradually broken (foaming), and the expansion ratio is conversely reduced. . Therefore, if a temperature that maximizes the expansion ratio is applied to the foaming agent without causing foam breakage and the foaming agent is cooled and fixed while maintaining the foamed state, a low-density foamed paper can be obtained most efficiently. The amount of the foaming agent is the density of the target paper,
It is determined by the performance and cost of the foaming agent to be used, and cannot be said unconditionally. However, when the above-mentioned foaming agent # 053 is used, the density is about 0.20 g / cm ³ and the pulp weight is 5%. % And a density of about 0.10 g / cm ^3, the blending amount was estimated to be about 15%. It was also confirmed that if the blending amount was further increased, the density would be less than 0.10 g / cm ³ .

The heating foaming agent is used by dispersing and stirring in about 5 times its own weight of water. An anionic surfactant such as a polycarboxylic acid type polymer as a dispersing aid is added to the heated foaming dispersion in an amount of 0.3 to 0.8% of the foaming agent, and the mixture is stirred to be effective in separating and dispersing aggregates. There is. Poise 521 and Poise 530 (both manufactured by Kao Corporation) are commercially available.
There is. Since these surfactants are hydrophilic, if they are used in combination with a sizing agent, if added in an amount of 1.0% or more, the sizing properties of paper (the effect of preventing bleeding of ink or the like) are undesirably reduced. In addition, as a dispersant to be added to the pulp slurry, in addition to the anionic surfactant such as the polycarboxylic acid type polymer, a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant are used. It is also possible.

After passing this foaming agent dispersion through a strainer made of a 100-150 mesh wire mesh or the like, or adding an anionic surfactant such as a polycarboxylic acid type polymer to the dispersion, a dispersing aid (hereinafter, referred to as a dispersion aid). This is added to about 0.5% of the solid content of the foaming agent and stirred, then blended into a pulp slurry and uniformly dispersed in the slurry. Even if the particles are coarser than 100 mesh, the aggregation of the foaming agent particles will not be eliminated, and when foamed, unevenness will occur and avatar-shaped fine projections will be formed. Also one
If the mesh size is smaller than 50 mesh, clogging with the foamed particles occurs, which is not appropriate. Needless to say, the papermaking raw material further contains a sizing agent, a chemical agent such as a paper strength agent, a filler such as a dye or a pigment, and the like, depending on the intended use of the product.

As for the dryer, there are a cylinder dryer, a Yankee dryer, and the like. In general, if a Yankee dryer is used, paper having a smooth surface can be obtained.
Slower speed resulting in higher costs. However, this can be arbitrarily selected depending on the end use, and is not particularly limited. If the surface temperature of the dryer is 130 to 155 ° C., the low-density foamed paper of the present invention can be obtained, but is not limited to this temperature range. The relationship between the dryer surface temperature and the web moisture, and the contact time between the web and the dryer are important factors for foaming. It can be said that it is possible to produce high density foamed paper.

Among the paper products manufactured using only wood pulp as a raw material, those belonging to a relatively low-density category are base papers for impregnation processing and have a density of 0.4 to 0.6 g / cm ³ . . Examples of even lower density materials include filter paper made of cotton linter pulp as a raw material, mosquito mat base paper manufactured by a special manufacturing method, and a fragrance-impregnated base material.
Its value is between 0.25 and 0.50 g / cm ³ . However, these papers do not provide the same heat insulation performance as polystyrene foam (polystyrene foam), and use a foaming agent that is more expensive than ordinary papermaking raw materials in the present invention. Less than .20 g / cm ³ (for the same basis weight of rice, the thickness is 25% more than the thickness of low-density foamed paper having a density of 0.25 g / cm ³ );
Preferably less than 0.18 g / cm ³ (also thickness 5
If the low-density foamed paper does not have an advantage from the technical point of view and the commercial value, it is considered that there is no advantage.

The products according to the present invention include, for example, insulated containers for instant noodles, heated beverages or frozen foods, as well as packaging materials for packing and transporting various products, cushioning materials laid under fresh vegetables and fruits, building materials, It is also useful as a cushion material for tatami floors and the like, and also as an impregnated base material for fragrances and liquid chemicals. In addition, the product according to the present invention has at least 5% or more of expandable capsule particles (hereinafter, referred to as “the particles”) in the substrate.
(Referred to as a foaming agent), and since the outer shell of the foaming agent is formed of a thermoplastic resin, the base sheet itself has heat embossing suitability and heat setting properties. Therefore, there is an advantage that the surface of the product formed in a sheet shape is partially provided with unevenness by post-processing, and the entire sheet is easily corrugated.

[0028]

EXAMPLES The present invention will be described below with reference to examples.
% And parts are parts by weight.Examples 1-3  Hardwood pulp (LBKP) 80% and softwood pulp (NB
KP) mixed pulp consisting of 20% Canadian freeness (CF)
The solution beaten to 580 ml in S) was used. As a foaming agent
Expancel 053WU (hereinafter referred to as # 053)
Stir in water three times its own weight to prepare an aqueous dispersion of the blowing agent.
Was. The aqueous dispersion of the foaming agent is used in accordance with JIS z8801 standard.
Pass the residue using a sieve 100-150 mesh and remove the residue 2
% Or less and 9% of the absolute dry weight of the pulp.
The foaming agent dispersion is added as described above.
(Polystron 194-7, manufactured by Arakawa Chemical Industry Co., Ltd.)
0.2%, starch (acedin AP-20, Daiwa Chemical
0.8%, alkyl ketene dimer series
(Spine Pine K287, Arakawa Chemical Industry Co., Ltd.)
0.1%, wet paper strength agent (WS515LX, Japan P
MC (manufactured by MC Co., Ltd.) in an order of 0.25%.
The moisture content of the wet web web before drying is 41% to 60%
Was adjusted as follows. The amounts of each of the above chemicals are all
The weight percentage of solids based on dry pulp.
The target weight of paper is 220 g / m²It is. Each moisture
Web adjusted to a rotary dryer (Jappo)
(Manufactured by Co., Ltd.).
A density foam paper was obtained.

[0029]Example 4  Residual 2% or less through 100 mesh standard sieve, dispersion aid
Examples 1 to 3 except that 0.5% of Poise 521 was added.
Similarly, a low-density foamed paper was obtained.

[0030]Examples 5 to 6  Change the foaming agent to Expancel # 007 and add
14% to the absolute dry amount, poise 530 each
Examples 1 to 3 except that 0.5% and 0.8% were added and stirred.
A low-density foamed paper was obtained in the same manner as described above.

[0031]Comparative Example 1  Use Expancel # 053 as a blowing agent and pass it through a standard sieve.
In the same manner as in Examples 1 to 3 without adding a dispersing aid,
To obtain a low-density foamed paper.

[0032]Comparative Examples 2 and 3  Using Expancel # 053 as a foaming agent, a standard sieve
Example 1 except that the mesh was passed through 60 mesh and 80 mesh
To 3, a low-density foamed paper was obtained.

[0033]Comparative Example 4  Using Expancel # 053 as a foaming agent, a standard sieve
2.29% residue when 100 mesh is passed
Conducted except for using the existing thing as aqueous dispersion of foaming agent
A low-density foamed paper was obtained in the same manner as in Examples 1 to 3.

[0034]Comparative Example 5  Same as Examples 1 to 3 except that the water content after pressing was 38%.
Thus, a low-density foamed paper was obtained.

Table 1 shows the physical properties of the low-density foamed papers obtained in Examples 1 to 6 and Comparative Examples 1 to 5.

[0036]

[Table 1]

[0037]Physical Properties and Properties of Low Density Foam Paper in Actual Machine Making
Effect of strainer and strainer Example 7  The pulp used for the actual papermaking is LBKP as before.
80%, 20% NBKP mixed pulp.
The freeness (CSF) is 600 g at a basis weight of 220 g /
Was. 9% of Expancel # 053 as a foaming agent, 10%
Residual content of 2% or less when passed through a 0 mesh strainer
Below, use an aqueous dispersion without a dispersing agent
Low-density foamed paper was obtained using a paper machine of a mold type. Also the size
The amount of chemicals used, such as
It is the same as the embodiment.

[0038]Example 8  Poise 530 (manufactured by Kao Corporation) is added as a dispersing aid.
A low-density foamed paper was obtained in the same manner as in Example 7 except for stirring.
Was.

[0039]Example 9  Pass through a 150 mesh strainer, dispersing aid poise
Example 7 was repeated except that 0.5% of 530 was added and the mixture was stirred.
Thus, a low-density foamed paper was obtained.

[0040]Example 10  Except for using a short-mesh multi-cylinder type paper machine
A low-density foamed paper was obtained in the same manner as in Example 9.

[0041]Example 11  Same as Example 7 except that the amount of the foaming agent added was increased to 18%.
Thus, a low-density foamed paper was obtained.

[0042]Example 12  Replace the foaming agent with Expancel # 007 and add 14
% To obtain a low-density foamed paper in the same manner as in Example 7.
Was.

[0043]Comparative Example 6  Add 9% Expancel # 053 to the foaming agent and add
Same as Example 7 except that it passed through an 80 mesh
Thus, a low-density foamed paper was obtained.

[0044]Comparative Example 7  Performed except that no strainer is added and no dispersant is added
A low-density foamed paper was obtained in the same manner as in Example 7.

[0045]Comparative Example 8  Same as Example 7 except that the water content after pressing was 65%
Thus, a low-density foamed paper was obtained.

[0046]Reference Example 1  Foamed with mixed pulp of LBKP 80% and NBKP 20%
No additives or dispersants are used, no strainer
The additive was added in the same manner as in the example, and after pressing, the moisture was dried by 52%.
Paper making at 139 ° C drying temperature using a round net Yankee type paper machine
Was. Target grammage is 220 g / m²And

Table 2 shows the physical properties of Examples 7 to 12, Comparative Examples 6 to 8, and Reference Example.

[0048]

[Table 2]

[0049]Evaluation  Avatar-shaped microprojections found in the hand-made papers of Comparative Examples 1-4 in Table 1.
No origin was found in the hand-made papers of Examples 1 to 6,
The effect of removing aggregates and dispersing the dispersant was confirmed. next
In both Examples 5 and 6, even if the amount of the foaming agent was increased, the avatar-like fine
No protrusions were observed, and the density was approximately 0.18 g /
cm³Higher product with less foaming agent than before
Quality low density foamed paper can be obtained
Was.

What has passed through a sieve coarser than 100 mesh,
When a dispersion having a residue of 2% or more was used even with 100 mesh, avatar-like fine projections appeared (Comparative Examples 2 to 4). As a result, it has been discovered that with a 100-mesh sieve or strainer, non-uniform formation due to aggregation of the foaming agent particles can be prevented if the residue is within 2.0%. The average particle diameter of the foaming agent Expancel # 053 used in the test is 5 to 30 μm, but # 007 has the same particle diameter, and other foaming agents have the same range of particle diameters. Needless to say, the same result can be obtained.

As shown in Table 2, even in the case of the actual machine, when a strainer was used (Example 7), no avatar-like fine projections due to uneven foaming were observed, and even when the foaming agent was further increased (Example 11, 12) It was demonstrated that a uniform foaming agent dispersing effect was obtained, as is known from the fact that good low-density foamed paper was obtained without any avatar-like projections.
In addition, the dispersant and the strainer for keeping the foaming agent in a uniform state are not effective unless they are diluted with water and added before pulp is added.

On the other hand, even in a paper machine having a multi-cylinder dryer (Example 9), the density was as low as 0.14 g / cm ^3, and it was confirmed that the present invention was useful regardless of the type of machine. Was done.

The present invention is characterized by pursuing how efficiently a wet paper web into which a foaming agent is uniformly mixed is efficiently foamed. That is, when the wet paper web moisture is reduced from around 30% by the dryer drying, the bonding strength between the celluloses increases due to the hydrogen bonding of the cellulose. Foamed paper is not obtained. The present inventors have conducted intensive studies on how the foaming conditions can be efficiently foamed by receiving the thermal energy from the dryer with a low web moisture, and the present inventors have made intensive studies. (1) The problem of how to uniformly disperse the foaming agent. And microscopic temperature distribution during drying. (2) Wet paper web moisture distribution when the foaming agent is effectively heated and foamed. This means that the dispersant and the foaming agent by the strainer are uniformly dispersed. When the wet paper web moisture is 41% or more, preferably 45% or more, foaming is efficiently performed, and the reduction of the web moisture is reduced. It has been found that it contributes to a reduction in drying energy and an improvement in productivity without any modification, and enables the production of low-density foamed paper by a method superior in cost.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mitsuo Suzuki 4-7-5 Ginza, Chuo-ku Oji Paper Co., Ltd. (72) Inventor Eigo Sano 1-1-1 Hisawa, Fuji-shi, Shizuoka Prefecture (72) Inventor Watanabe Yasuhito 888 Otsuka 888, Numazu-shi, Shizuoka F-term (reference) 4L055 AG33 AG71 AG74 AG89 AG94 AH29 AH33 AH34 AJ08 AJ10 BD10 BE20 EA13 EA16 FA11 FA14 FA16

Claims (6)

[Claims] 1. A method for producing a low-density, bulky paper by foaming a paper web formed by mixing a heating foaming agent into a pulp and heating the paper web, wherein a heat-expandable heat foaming agent is added to the pulp. Using microcapsules,
The capsules are uniformly dispersed in a pulp slurry. At this time, the foaming agent is dispersed such that at least 100 mesh passes occupy 98% or more in the pulp slurry. A method for producing a low-density foamed paper, comprising forming a paper and heating and foaming the paper. 2. When the pulp slurry is formed as a wet paper web on a wet part of a paper machine, the moisture content of the wet paper web before heating and foaming is at least 41 to 60%.
2. The method for producing a low-density foamed paper according to claim 1, wherein the foaming is carried out by heating while keeping the temperature within the range. 3. The method for producing a low-density foamed paper according to claim 1, wherein a surfactant is used in combination to uniformly disperse the heating foaming agent in the pulp slurry. 4. A wet paper web formed by adding the heating foaming agent to the pulp slurry at a solid content of 5 to 20% based on the weight of the pulp and then uniformly dispersing to form a wet paper web. After the water content of 41 to 60%,
The method for producing a low-density foamed paper according to claim 2 or 3, wherein the web is heated and foamed through a dryer to obtain a low-density paper sheet. 5. A microcapsule as a heating foaming agent
After passing through a strainer or screen having a sieve of 00 to 150 mesh, the capsules are added to the pulp slurry and mixed uniformly, and the moisture content of the wet paper web before heating and foaming is reduced to 41 to 60%. 3. The method for producing a low-density foamed paper according to claim 1 or 2, wherein the foamed article is heated and foamed after being in a state. 6. A low-density foamed paper produced by the method according to claim 1.