JPS62268900A - Polyolefinic wet nonwoven fabric - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a polyolefin wet-laid nonwoven fabric, and more specifically, a polyolefin wet-laid nonwoven fabric that has excellent hydrophilicity and liquid retention properties, and also has excellent mechanical properties such as tensile strength. Water resistance that is widely used in fields that require shallow water properties, liquid absorption, and liquid retention, such as electrical materials such as liquid-retaining separators for sealed batteries, α-absorbing sanitary materials, and wiping cloths. and a polyolefin wet-laid nonwoven fabric with chemical resistance.

[Prior Art] Polyolefin-based synthetic pulp (hereinafter simply referred to as "synthetic pulp") has a good fibril structure and can be easily synthesized by employing auxiliary bonding means such as heat fusion. Its use has increased in recent years because it can yield paper.

Since these synthetic pulps are hydrophobic in nature, many methods have been used to improve their dispersibility in water during the papermaking process and their wettability after papermaking.
No. 5 and Japanese Unexamined Patent Publication No. 59-59910 disclose methods of improving water dispersibility and water retention by using polyvinyl alcohol, which is a hydrophilic material.
JP-A-49-118916 and JP-A-58-20311
No. 8 and others disclose a method of improving water dispersibility and mechanical properties by using a hydrophilic polymer.

In addition, although it is not a synthetic pulp, as a material that simply makes polyolefin fibers hydrophilic, η Riba is used in Japanese Patent Application Laid-Open No. 60-19
No. 4113 discloses a method of melt blending a polyolefin resin and a hydrophilic resin. In addition, JP-A No. 60-246869 and JP-A No. Kaisho 58-81
No. 679, etc., discloses a method for making fibers hydrophilic using graft copolymerization.

As other materials, hydrophilic mats made of ultrafine glass fibers with an average fiber diameter of 5 μm or less that utilize capillarity are known as, for example, battery separators.

[Problems to be Solved by the Invention] The synthetic pulp of JP-A No. 58-203118, which has been subjected to hydrophilic treatment, has excellent water dispersibility and is useful for producing high-quality paper using ordinary papermaking methods. considered to be a thing.

However, these materials do not have practical strength as paper unless they are compacted by heating and fusing after papermaking, and even if they remain hydrophilic, they lose liquid retention. Therefore, it could not be used for applications requiring liquid retention.

In addition, the above-mentioned Japanese Patent Application Laid-open No. 59-59910 discloses a fluff-like material with a low density, but although this material has sufficient liquid-retaining properties, it does not have mechanical properties such as shape-retaining properties. It has no properties at all, and cannot be applied to applications that require strength, such as battery separators and wiping cloths.

The hydrophilic treatment of fibers by graft copolymerization in JP-A-60-246869 is based on acrylics, polyamides, which are thought to easily generate radicals in fibers as backbone polymers,
Although it can be applied to polyvinyl alcohol or polyester fibers, it is virtually impossible or extremely difficult to generate radicals in polyolefin fibers as in the present invention, making it impractical. is considered to be low.

Furthermore, mats made of ultra-fine glass fibers used for battery separators, etc. have a slow water absorption rate and poor mechanical properties, so they are not versatile and are not satisfactory as base materials for separators. It wasn't.

[Means for solving the problems] The present invention provides polyolefin synthetic pulp with at least 5
In the wet-laid nonwoven fabric containing 0% by weight, the polyolefin synthetic pulp contains 2 to 30% of a hydrophilic treatment agent containing at least one type of polyfunctional monomer having two or more functional groups based on the weight of the pulp. Relating to a polyolefin wet-laid nonwoven fabric, which is a polyolefin-based wet-laid nonwoven fabric, characterized in that the nonwoven fabric has a basis weight of 50 to 4003/m" and an apparent density of 0.05 to 0.3 g/cm3. .

[Function] The present invention is a wet-laid nonwoven fabric mainly composed of polyolefin synthetic pulp, which has a low density that could not be obtained with conventional wet-laid nonwoven fabrics, yet has sufficient decoy mechanical properties, and has hydrophilic properties. The purpose of the present invention is to obtain a wet-laid nonwoven fabric that is water resistant and chemical resistant and has water resistance and liquid retention properties that are much better than those of conventional fabrics.

To this end, the present inventors have conducted extensive research, and as a result, a hydrophilic treatment agent containing at least one type of polyfunctional monomer having two or more functional groups is attached and polymerized to synthetic pulp, and the pulp is When paper is made, sufficient mechanical strength and excellent hydrophilic and liquid-retaining properties can be obtained without the need for consolidation as in conventional methods, and this paper also has water and chemical resistance. The heading completes the invention.

The synthetic pulp used in the present invention may be any commonly used synthetic pulp and does not require anything special at all, but it is desirable to use one with a high degree of fibrillation in order to improve liquid retention.

These polyolefin synthetic pulps have a 1iH fibril structure, so unlike simple fibrous materials,
It has the effect of further improving liquid retention through hydrophilic treatment, and has excellent chemical resistance and electrical resistance.
It forms the skeleton of the wet-laid nonwoven fabric of the present invention and provides permanent shape retention performance. Therefore, it is necessary that the wet-laid nonwoven fabric of the present invention contains at least 50% by weight, and if 50% by weight is ungrooved, a nonwoven fabric with practical strength cannot be obtained, or a nonwoven fabric with no shape Even if it were possible to retain this, it would be unsuitable because it would only have poor liquid retention and chemical resistance.

Next, a polyfunctional monomer and a hydrophilic treatment agent containing at least one polyfunctional monomer will be explained.

Examples of polyfunctional monomers include diene monomers that have at least two double bonds and form three-dimensional crosslinks through radical or ionic polymerization, and monomers that have vinyl groups at both ends of a certain segment. Alternatively, monomers having three or more carboxyl groups that form three-dimensional crosslinks through condensation are known. All of these monomers can be used as the polyfunctional monomer of the present invention, but from the viewpoint of ease of obtaining hydrophilicity, ease of reaction, or durability, polyalkylene oxide segments may be included. It is advantageous to use monomers having vinyl groups such as acrylic or methacrylic at both ends, especially monomers having alkylene oxide segments with an average number of segments of 2 to 30, most preferably 4 to 15. The monomers contained therein have an excellent balance between hydrophilicity, liquid retention, mechanical properties, and chemical resistance, and can be said to be the best ones. The reason for this is that when the average number of segments' is less than 2, the solubility in water is poor and the workability when adhering and polymerizing monomers to synthetic pulp is poor, and the crosslinking density becomes excessive after polymerization. As a result, this impedes the hydrophilic liquid retention effect and the bonding between the pulps during paper making, and conversely, when the number of segments exceeds 30, the crosslinking density is low, making it difficult to make the synthetic pulp hydrophilic. The treatment agent may be removed or it may be attacked by water or chemicals, resulting in poor chemical resistance.

The hydrophilic treatment agent is used by being mixed with 100% of the above polyfunctional monomer or other hydrophilic monomers.

Hydrophilic monomers to be mixed include well-known hydrophilic monomers such as acrylic acid, acrylamide, itaconic acid, vinylibirrolidone, and maleic acid, which have a vinyl group and a carboxyl group or amide group at the end. is preferable,
In particular, acrylic acid or methacrylic acid has excellent hydrophilicity and acid resistance, so it is advantageous when the nonwoven fabric of the present invention is applied to liquid-retentive separators for acid batteries, etc.

Therefore, these hydrophilic monomers can be appropriately selected depending on the purpose of use, and when a monomer having a carboxyl group is used in the separator, it has properties other than acid resistance, such as It is further advantageous because it has the effect of adsorbing cationic impurities such as sodium ions and antimony generated from the electrodes and electrolyte.

The hydrophilic treatment agent containing these polyfunctional monomers is polymerized and adhered to the surface of the synthetic pulp to form a three-dimensional crosslinked structure, and exhibits the effect of making the synthetic pulp hydrophilic.
Its hydrophilicity is made permanent. The reason for this is that, as mentioned above, the fibril structure of synthetic pulp and the complex and very large surface area and surface condition resulting from the fibril structure make the hydrophilic treatment agent effective against mechanical effects such as friction. This is thought to be because the treatment agent, which is hydrophilic in wood, has a three-dimensional crosslinked structure and is therefore extremely robust even when exposed to chemical influences such as chemicals.

In addition to the effect of making synthetic pulp hydrophilic, the hydrophilic treatment agent has another important effect.

This is because conventional synthetic pulp can only be achieved practical strength by compacting it with a heat roll or the like after papermaking, and if necessary, by partially heat-sealing it. Low-density materials with less than 0.3 g/cm3 have no shape retention properties, or
Synthetic pulp treated with the hydrophilic treatment agent of the present invention has poor strength and no practical value, but it not only has excellent water dispersibility and product homogeneity, but also has excellent dispersibility in water and product homogeneity. By simply drying with an appropriate drying means such as a dryer, a practical strength of 0.53/cm width or more per unit area weight (g/='), or 1 g/cm width or more under optimal conditions, can be obtained. This is also an extremely important effect of the hydrophilic treatment agent.

The reason for this is not clear, but it may be that the polymerized hydrophilic treatment agent has a reinforcing effect on the fine fibrils, which are a characteristic of synthetic pulp, and as a result increases the entanglement strength between the fibrils. This is thought to be because the hydrophilic treatment agent itself has a mutual self-adhesion or adhesive action.

In order to obtain the above-mentioned hydrophilic effect and strength reinforcing effect, the adhesion rate of the hydrophilic treatment agent to the synthetic pulp is an extremely important factor.

Hereinafter, further explanation will be given with reference to the drawings. FIG. 1 is a diagram showing an example of the relationship between the adhesion rate and water absorption rate of a hydrophilic treatment agent made of 100% polyethylene glycol dimethacrylate. FIG. 2 is an explanatory diagram showing that the best water absorption rate is obtained when 4 to 10 weight 1% of the water is deposited. Although not shown in the figure, when the type of hydrophilic treatment agent is changed, the best point is slightly different from that in Figure 1, but it is generally thought to exist in the range of 5 to 15%. . Figure 2 is a diagram showing an example of the relationship between the adhesion rate of a hydrophilic treatment agent and the tensile strength.The tensile strength increases by approximately 30% by weight compared to the adhesion rate of the hydrophilic treatment agent. , the rate of increase in strength decreases slightly at a one-size fit rate higher than that. Although not shown in the drawings, if the adhesion rate of the hydrophilic treatment agent exceeds 30% by weight, it is not preferable because although the strength increases, the rigidity of the product also increases and there is a risk of defects such as breakage due to bending.

From the above, it is necessary that the adhesion rate of the hydrophilic treatment agent is 2 to 30% by weight, and optimally 5 to 15% by weight.
If the adhesion rate of the hydrophilic treatment agent is less than 2%, both hydrophilicity and mechanical properties are insufficient and it is not practical, and if it exceeds 30% by weight, the water absorption rate decreases and
The deep liquid properties are also lowered, and the obtained nonwoven fabric is rigid and has poor flexibility, which is not preferable.

Next, I will briefly explain the methods of polymerizing and adhering a hydrophilic treatment agent to synthetic pulp.There are two methods: immersing the synthetic pulp in the treatment agent, removing the excess, and then polymerizing it, and spraying the treatment agent onto the synthetic pulp. Various methods can be considered, such as a method in which the hydrophilic treatment agent is sprayed on the water and then polymerized, but in any case, in the present invention, the hydrophilic treatment agent contains at least 60% or more of the monomers,
Since 100% of the resin is polymerized and effectively utilized, it is important to deposit the required amount. In particular, if more treatment agent is attached than necessary, independent polymers may be generated on surfaces other than the surface of the synthetic pulp, causing clogging or free impurities, or adhesion to the dryer during drying. This is undesirable because it reduces the quality of the product.

Further, the polymerization method may be any method such as the well-known method of polymerizing under steam and pressure, or the method of polymerizing monomers using ultraviolet rays, electron beams, high frequency waves, etc. It is also possible to add polymerization initiators such as oxides, azobisisobutylnitrile, or acidic sodium sulfite, and redox catalysts such as cerium salts.
It can be selected as appropriate depending on production conditions.

Adding a $filling agent to these hydrophilic treatment agents is also suitable for applications that require denseness, such as battery separators. These self-filling disintegrating agents make it possible to increase the density of the nonwoven fabric, ensure liquid retention ability, and enhance voltage resistance, heat resistance, and chemical resistance. Also, if necessary, hydrophilic treated synthetic pulp, E1 It is also possible to make paper by mixing fine glass fibers or synthetic fibers, and in particular, if 5 to 30% by weight of glass fibers with a fiber diameter of 5 μm or less are mixed, the liquid retention property and water absorption rate can be further improved. This is suitable because it allows for

Next, to briefly describe the manufacturing method of wet-laid nonwoven fabric, at least 50% by weight of hydrophilized synthetic pulp and glass fibers, synthetic fibers, etc. mixed as necessary are prepared using the well-known inclined short screen method. It is dispersed in water using a one- to multi-layer paper machine such as a circular mesh type, excess water is removed, and it is collected on a screen and then heated and dried to obtain the wet-laid nonwoven fabric of the present invention.

The hydrophilized synthetic pulp used in the present invention has all the properties necessary for wet papermaking, such as water dispersibility, accumulation, and drying properties, so it can be applied to all existing wet papermaking equipment. No special equipment is required.

The nonwoven fabric of the present invention has a basis weight of 50 to 400 g/m',
It is made to have a density of 0.05 to 0.33/cm3.

The reason for this is that the area weight range that has practical value as a hydrophilic and liquid-absorbing material is 50 to 400 g/m';
If it is less than 0.3 g/m2, mechanical properties such as liquid retention and strength will be poor, and if it exceeds 400 g/m2, it will become a thick plate with poor flexibility, and uniform production will be difficult. This is not desirable. In addition, the apparent density of wet-processed nonwoven fabric is 0.
．． 053/cm3 without grooves, it has liquid retention but poor mechanical properties; conversely, when it exceeds 0.3g/cm3, it has excellent mechanical properties but poor liquid retention. Undesirable.

These wet-laid nonwoven fabrics according to the present invention have a water absorption rate of 10
c+n/10 min or more, liquid retention rate of 200% or more, mechanical strength of 0.5 g/cn+width bag g/m) or more, and exhibits excellent quality, especially when the nonwoven fabric has a basis weight of 100 to 300 g/m. ', the apparent density is 0.15 to 0.2
For those in the range of 5g/cm3, the water absorption rate is 15
cm/10m1n or more, liquid retention rate under 10G gravity is 30
0% by weight or more, and the strength is 13/cm/(g/cm
') has an excellent value.

The water absorption rate, liquid retention rate, and tensile strength used in the description of the present invention were measured under the following conditions.

(Water absorption rate) A 1.5 cm wide test piece is vertically immersed with 1 cm of the end of the test piece in water, and the length of vertical rise of water after 1° is defined as the water absorption rate.

(Liquid retention rate) The pinching pressure between two stainless steel plates is 20
08/ctn', sandwich a test piece that is sufficiently moistened with water, rotate the test piece at high speed in the plane direction, apply IOC gravity to the center of the test piece, and after 1 minute, add water to the weight of the wet nonwoven fabric. The weight of the liquid was measured, and the ratio was taken as the liquid retention rate.

(Tensile strength) A 5 cm wide test piece was pulled at a speed of 100 m+/min using a constant speed elongation tester, and +iA was calculated per unit width and per unit weight for one measurement.

The liquid retention property and water absorption rate of the wet-laid nonwoven fabric of the present invention are as follows.
l +r; Snake rrz > h +n
-q, -NIId! +1
6'+ 1-+ +ffi-u-ru. Therefore, the wet-laid nonwoven fabric of the present invention does not have the phenomenon that known liquid-retaining materials using superabsorbent polymers swell or feel slimy when soaked with water.

This makes it more certain that the wet-laid non-woven fabric of the present invention is suitable for, for example, battery separators, etc., where swelling of the base material should be avoided. caused by microfibrils,
On the contrary, sufficient liquid retention capacity can be obtained without causing any chemical changes in the nonwoven fabric during rough hitting due to capillarity, mesh formation, and the affinity for water created by the hydrophilic treatment agent. This has a further advantageous aspect since it also facilitates dewatering when it becomes necessary to dehydrate the product.

Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited to these Examples.

[Example 1: 100 parts by weight of synthetic pulp was chopped into polyethylene glycol having 15 ethylene glycol segments and an ammonium persulfate catalyst was added] / 7″ 1-1-1. Pubma / 711L
2 to 30 parts by weight of an aqueous solution of L-1 was applied to 1 inch, and heated and polymerized in a steamer at 100°C for 1 hour to obtain a hydrophilic product with a polymer attached at the adhesion rate shown in Table 1. A synthetic pulp of high quality was obtained.

Next, this material was passed through a 25 cm square test paper machine.
Paper was made to have a basis weight of 2008/m' and a thickness of 1lnff+ to obtain a wet-laid nonwoven fabric according to the present invention.

The obtained nonwoven fabric was measured for tensile strength, water absorption rate, liquid retention, durability, etc., and the results are shown in Table 1.

These wet-laid nonwoven fabrics according to the present invention had the excellent performance shown in Table 1, and had very high practical value as a hydrophilic and liquid-retaining material.

Also, for comparison with these, those without hydrophilic treatment agent,
those in which the amount of the processing agent is further changed beyond the scope of the present invention;
Experiments were also conducted on polyolefin composite fibers for wet use to which the same amount of hydrophilic treatment agent as in Example 1 was added, and the results are shown in Table 1. However, these fibers had no strength at all. Or, they were clearly inferior in liquid retention and durability, and had no practical value at all.

In addition, durability was measured after 10 hours of water resistance and 1 month of acid resistance in 40% sulfuric acid heated to 80°C.
Mechanical resistance was measured by measuring the water absorption rate after 1 hour using an ICI pilling tester, and a retention rate of 75% or more was determined as 0140%.
Those above were indicated as △, and those below 40% were indicated as X.

[Example 2] Using the same formulation as shown in Experiment No. 3 of Example 1, only the apparent density of the obtained nonwoven fabric was changed to create an example for comparison with the example according to the present invention. Then, the same test as in Example 1 was conducted, and the results are shown in Table 2.

The apparent density according to the present invention is 0.05 to 0.3 g/cr
rr showed good performance as shown, but the comparative example had poor shape retention, hydrophilicity, etc., and could not be used for practical purposes.

[Example 3] In order to investigate the influence of the number of ethylene glycol segments,
Polyethylene glycyl diacrylate monomers with various numbers of segments were applied to synthetic pulp in an amount of 10 parts by weight, and polymerization was carried out under the same conditions as in Example 1, resulting in a fabric weight of 15.
A nonwoven fabric with a diameter of 0.8/m' and a thickness of 0.8 mm was prepared.

The results are shown in Table 3. When the number of segments is 1 and there is no groove, workability is poor due to poor water dilution during polymerization, and as a result, it does not adhere uniformly to the synthetic pulp, resulting in lumps. Furthermore, as shown in the table, those having 30 or more segments were poor in hydrophilicity and liquid retention, and were also inferior in durability.

The material according to the present invention, like those shown in Examples 1 and 2, was optimal as a durable liquid retaining material.

[Example 4] In order to investigate the influence of monomers other than polyfunctional monomers as a hydrophilic treatment agent, synthetic pulp was treated with the hydrophilic formulations shown in Table 4 under the same conditions as in Example 1. Approximately 1 liter of treatment agent is added to the synthetic pulp.
A wet-laid nonwoven fabric having the same basis weight and thickness as in Example 1 was prepared by adhering and polymerizing O weight %, and the obtained nonwoven fabric was evaluated.

The results are shown in Table 4, and the hydrophilic treatment agent containing 10 to 50% by weight of monomers having a carboxyl group has excellent hydrophilicity and liquid retention properties, and has an effect of improving strength. was also found to be excellent.

[Example 5] Dimethacrylate monomer 8 having 812 polyethylene glycol segments
About 12 parts by weight of a hydrophilic treatment agent mixed with 0% by weight and 20% by weight of acrylic acid was applied to synthetic pulp under the same conditions as in Example 1 to prepare a hydrophilic synthetic pulp. 80 parts of synthetic pulp and 20 parts of glass fiber with an average fiber diameter of 1.2 μm were mixed to make paper, with a basis weight of 2:303/m'.
A battery separator base material using the wet-laid nonwoven fabric of the present invention having a thickness of 1.2 mm was obtained.

This separator base material was
Table 5 shows the results of a test in which the battery was used in the sealed acid battery No. 1 and repeated charge/discharge tests, and the electrical performance was investigated.

The discharge test was conducted at an average discharge current of 13A and a final voltage of 2.
．． The time until the voltage reached 8V was measured.

In addition, for comparison, the same test was conducted on a material made of 100% glass fiber and a material made of a mixture of glass fiber and acrylic fiber, which have been conventionally used as battery separator base materials, and the results were as follows. Also shown in Table 5.

As a result, the base material using the wet-type wS cloth according to the present invention has the advantages of superior liquid retention, long life, and less self-discharge than the conventional material. It also had the economical advantage of being able to be produced at a much lower cost.

[Table 5 with blank spaces below] [Effects] The polyolefin wet-laid nonwoven fabric of the present invention is a product with an unprecedentedly low density that can be obtained by a manufacturing method suitable for high-speed mass production called a wet papermaking method. , has extremely high economic efficiency, and also has excellent productivity and uniformity of quality.

Since the main component is polyolefin synthetic pulp, which is a stable and inexpensive raw material, it is possible to provide a product of much higher quality and at a lower cost than before.

In addition, since the polyolefin wet-laid nonwoven fabric of the present invention is composed of synthetic pulp and a hydrophilic polymer, it has no impurities and is extremely safe. It can be applied to necessary sanitary materials, etc., and since both synthetic pulp and crosslinked polymers have extremely high durability, they can be used in battery separators that require acid resistance and chemical resistance, for example. It can be said that it is the most suitable for As described above, the polyolefin wet-laid nonwoven fabric of the present invention has excellent versatility and can be applied to an extremely wide range of uses.

Since the synthetic pulp constituting the present invention 6 polyolefin wet-laid nonwoven fabric is essentially thermoplastic, it has heat-sealability and heat-fusion properties. It also has many advantages in terms of processability, as it can be layered with other materials and heat-sealed.

Therefore, the polyolefin wet nonwoven Ia of the present invention satisfies all the essential objectives such as improving hydrophilicity, liquid retention, and base material strength, and also has excellent resistance such as chemical resistance. Moreover,
This is a new product that has productivity, safety, economy, and versatility, and is unprecedented.

Patent applicant Nippon Vilene Co., Ltd. Treatment agent adhesion rate
(%) Wakae with processing agent (%) Procedural amendment (Sword August 4, 1986)

Claims (8)

[Claims] (1) In a wet-laid nonwoven fabric containing at least 50% by weight of polyolefin-based synthetic pulp, the polyolefin-based synthetic pulp is treated with a hydrophilic treatment agent containing at least one type of polyfunctional monomer having two or more functional groups based on the weight of the pulp. 2 to 30% by weight of the nonwoven fabric is adhered and polymerized, and the nonwoven fabric has a basis weight of 50 to 400 g/m^2 and an apparent density of 0.05 to 0.3 g/cm^3. Polyolefin wet-laid non-woven fabric. (2) The polyfunctional crosslinked monomer contains a polyalkylene oxide segment, and the average number of segments is 2 to 30.
The polyolefin wet-laid nonwoven fabric according to claim 1. (3) A diacrylate of a polyfunctional crosslinked monomer with an average number of alkylene oxide segments of 4 to 15, and/
Alternatively, the polyolefin wet-laid nonwoven fabric according to claim 2, which is dimethacrylate. (4) The hydrophilic monomers include 50 to 90% by weight of a polyfunctional monomer containing a polyalkylene oxide segment and 50 to 10% by weight of a vinyl monomer having a carboxyl group.
The polyolefin wet-laid nonwoven fabric according to claim 1, which is a mixture of. (5) The water retention rate of wet nonwoven fabric under gravity of 10G is 300
% or more by weight of the polyolefin wet-laid nonwoven fabric according to claim 1. (6) The polyolefin wet-laid nonwoven fabric according to claim 1, wherein the wet-laid nonwoven fabric has a water absorption rate of 15 cm/10 min or more. (7) Tensile strength of wet nonwoven fabric is unit weight (g/m^2)
The polyolefin wet-laid nonwoven fabric according to claim 1, which has an amount of 1 g/cm or more per width. (8) The wet-laid polyolefin nonwoven fabric according to claim 1, which is used as a separator for sealed acid batteries.