JPH02112460A - Sheet having high strength - Google Patents

Abstract

PURPOSE:To obtain a high-strength sheet having excellent filtration performance, dust-collecting property, etc., by using ultrafine fibers having a specific average fiber diameter and thick fibers composed of a thermoplastic fiber having a melting point lower than the melting point of the ultrafine fiber and partially bonding the ultrafine fiber to the thick fiber with heat. CONSTITUTION:The objective sheet having excellent bacteria-barrierness, liquid- absorbing property and heat-insulation and suitable as various filters, wipers, laps, heat-insulation materials, etc., is a random mixture of (A) ultrafine fibers having an average fiber diameter of 0.1-0.8mum and composed of polypropylene, polyethylene terephthalate, etc., and (B) thick thermoplastic fibers having an average fiber diameter of >=10mum and a meting point lower than that of the ultrafine fiber by 10-200 deg.C (e.g., fiber of nylon 6 or polypropylene). The sheet is produced by partially bonding the ultrafine fibers A and the thick fibers B with heat.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a high-strength sheet material containing ultrafine fibers.

More specifically, regarding sheet-like materials that have excellent filter performance, bacterial barrier properties, dust absorption, liquid absorption, and heat insulation properties, and are also highly strong, we will focus on ultra-fine sheets that are particularly suitable for various filters, wipers, wraps, insulation materials, etc. This invention relates to a high-strength fiber sheet.

However, since the sheet-like material referred to in this specification substantially corresponds to a nonwoven fabric, the nonwoven fabric will be described below.

[Conventional technology]

Nonwoven fabrics made of ultrafine fibers, especially ultrafine fiber nonwoven fabrics obtained by melt blowing, have excellent filter performance, grouper barrier properties, dust absorption properties, liquid absorption properties, heat insulation properties, etc., and are used in a variety of applications by taking advantage of these characteristics. It's coming.

For melt blowing methods, see Industrial and Engineering Chemistry.
al and Engineering Chemises
try) Volume 48, No. 8 (P, 1342-1346)
, 1956, disclosed the basic apparatus and method. Additionally, Japanese Patent Publication No. 56-33511 and Japanese Patent Application Laid-open No. 55-1.42757 disclose methods for producing ultrafine fibers such as polyolefins and polyesters.

On the other hand, the following are known as nonwoven fabrics in which thick short fibers are mixed with ultrafine fibers. In other words, Special Public Interest Publication 1986-
No. 30065 states that at least 30cm is a mixture of monopolar IH fiber and crimped staple fiber with a larger diameter.
An elastic fibrous web for thermal insulation having a loft of ra/g is disclosed.

Also, JP-A-55-30498 and JP-A-591
No. 83723 discloses a wiper containing ultrafine fibers and crimped thick short fibers.

[Problems to be solved by the invention] Nonwoven fabrics made only of ultrafine fibers, especially ultrafine fiber webs obtained by melt blowing, are high-quality porous bodies with extremely small pore sizes, so they have excellent filter performance, bacterial barrier properties, It has the advantage of being excellent in dust absorption, liquid absorption, heat insulation, etc., but on the other hand, it has the problem of being low in strength and its uses are greatly limited. Therefore, melt blown webs are rarely used alone, and generally,
It is used by laminating it with a high-strength nonwoven fabric such as a spunpond nonwoven fabric or a tJ'tH material, and there is a problem in terms of performance and cost.

On the other hand, in the above-mentioned Japanese Patent Publication No. 61-30065, the purpose of mixing thick crimped staple fibers with pole 11I fibers is to increase the bulk of the web (increase porosity), thereby improving insulation properties. That's what I got. Also, Unexamined Patent Publication Edict 55-3
0498 Textile, JP-A-59-183723 No. 1
The purpose of mixing thick crimped short fibers was to improve the porosity (increase bulk) of the web, thereby increasing the dust absorption and liquid absorption properties that are the characteristics of a wiper. In this way, the aims of short fiber mixing in the known technology are 1. This is due to the increase in porosity due to increased bulk.

Furthermore, in the case of JP-A No. 55-30498, as is clear from the examples, polypropylene, polyethylene, and acrylic polymers are used as the ultra-fine fibers, and polyethylene terephthalate and polyethylene terephthalate are used as the ultra-thick fibers to be mixed.
Not only are different materials such as nylon and nylon 6.6 used, but also extra-large fibers with a melting point higher than that of ultra-fine fibers are used.

Therefore, even if thermally bonded, the ultrafine fibers and the ultralarge fibers are not sufficiently bonded, and the ultrafine fibers are essentially thermally bonded to each other. As a result, not only the characteristics of the ultra-fine fibers were lost, but also the reinforcing effect of the ultra-thick fibers was hardly exhibited, resulting in an insufficient strength-improving effect. On the other hand, since a relatively high temperature is required to create a thermal bond between the ultra-fine fibers and the thick fibers, in this case, the ultra-fine fibers made of low-melting point materials are severely damaged, hardening and becoming brittle. There was a problem in that not only did the performance of the material deteriorate, but also the strength hardly improved, and on the contrary, the strength (particularly the tear strength) often decreased. Further, the same problem can be seen in the case of the non-woven fabric 1 disclosed in Japanese Patent Application Laid-Open No. 59-183723.

The present invention provides a single-layer type high-strength micro-fiber nonwoven fabric that does not impair the features of the micro-fiber web described above as much as possible, and does not involve lamination with other high-strength non-woven fabrics such as spunbond. The purpose is to do something.

[Means for Solving the Problems] An object of the present invention is to provide fibers with an average fiber diameter of 0.1 to 8. O/Rn
A sheet-like material in which ultrafine fibers of , and is achieved by a high-strength sheet material in which at least the low melting point thermoplastic fibers and the ultrafine fibers are partially thermally bonded.

The ultrafine fibers of the present invention include polyolefins such as polypropylene and polyethylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, and nylon 6
, polyamides such as nylon 6.6 and their copolymers, polyvinyl chloride, acrylic and acrylic copolymers, polystyrene, polyarylene sulfide, polysulfone, and inorganic fibers. In the present invention, it is preferable to select thermoplastic fibers, particularly thermoplastic polymer fibers of the same type that are compatible with the mixed fibers, in order to increase the thermal bonding strength between the ultrafine fibers and the mixed fibers.

The ultrafine fibers referred to in the present invention have an average fiber diameter of 0.1
It is preferable to use fibers 111 with a diameter of ~8.0 μm or less, preferably an average fiber diameter of 0.5 to 6.0 μm, particularly preferably 1.0 μm.
The fibers preferably have an average fiber diameter in the range of 0 to 5.0 μIn. If the average fiber jnf: diameter is 0.1p or less, it is not preferable because although it is flexible, the fiber strength is low and the fluff may fall off, which limits its uses.

On the other hand, if it is 8.0 or more, the strength of the nonwoven fabric becomes high, but on the other hand, it is not preferable because the above-mentioned features of the extremely high quality fibers, such as filter performance, bacterial barrier properties, dust absorption properties, liquid absorption properties, and heat insulation properties, are inferior.

The mixed fiber of the present invention has a melting point of 10 to 200% higher than the melting point of the ultrafine fiber.
It is a thermoplastic fiber with a low melting point.

Such mixed fibers are selected from materials such as polyolefins such as polypropylene and polyethylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides such as nylon 6 and nylon 6.6, and polyacrylonitrile. Examples include copolymers and blends of In the present invention, copolymers and those with a relatively low degree of polymerization are preferred because they can easily lower the melting point.

Further, the number of material components may be two or more.

The mixed fibers of the present invention may or may not be crimped, but if they are crimped, the ultrafine fiber nonwoven fabric will be bulkier and will have better dust absorption properties.
It has improved liquid absorption and is suitable for wiper applications. In addition, it is also preferable to use the material as a heat insulating material because crimping improves heat insulating properties.

Furthermore, since pressure loss and dust retention U are improved, it is also preferable for use in filters.

The crimp ratio is preferably 15% or more.

The fiber diameter (denier) of the mixed fibers is important because it affects the strength of the nonwoven fabric. In the present invention, it is preferable to use fibers having an average fiber diameter of 10 μm or more, preferably 15 to 60 nm, particularly preferably 20 to 45 nm. It has been found that the larger the average fiber diameter, the better the tensile strength and tear strength of the nonwoven fabric when mixed at the same weight ratio, and that sufficient strength can be obtained when the average fiber diameter is 10μ or more. The fiber length of the composite fibers is not particularly limited, and may be short fibers or long fibers. Short fibers are preferred in order to mix randomly and uniformly in ultrafine fibers, and 3 to 10
0 mm, especially 10-80 mm is preferred.

The melting point of the mixed fiber is 10 to 200" higher than the melting point of the ultrafine fiber.
It is necessary that C is low. Preferably 20-150°C
1 Particularly preferably 25 to 100°C.

If this melting point difference is less than 10°C, the melting points of the mixed fibers and the ultrafine fibers are too close, and in the thermal bonding process, in addition to adhesion by the mixed fibers, there is also a lot of thermal adhesion between the ultrafine fibers, resulting in a web of ultrafine fibers. Not only are the various above-mentioned features of the material significantly reduced, but the tear strength also decreases and the hand becomes extremely hard.

On the other hand, if the melting point difference exceeds 200"C, the melting point of the mixed fibers is too low"ζ, which may cause problems such as peeling depending on the conditions of subsequent use.

In this way, only when the joining point difference is in the range of 10 to 200'C, the filter performance, which is a feature of the ultrafine fiber web, can be improved.
High strength can be achieved with almost no loss in bacterial barrier properties, dust absorption properties, liquid absorption properties, and heat insulation properties.

Although this phenomenon is not necessarily clear, it can be considered as follows. In other words, because the difference in melting point between ultrafine fibers and mixed fibers is more than 10°C, it is possible to heat-seal and bond the ultrafine fibers with almost no thermal adhesion between them. It will not be damaged. Further, if there is a large amount of mutual thermal bonding between the ultrafine fibers, the tear strength will be particularly low in the part where there are no reinforcing fibers, that is, mixed fibers, and tearing will occur from this part, which is not preferable. Moreover, I
Thermal bonding is possible centered on the intersection of the Ir and i composite fibers, and even after heat fusion bonding, the mixed fibers can maintain almost their fiber shape, thus achieving high strength.

The melting point in the present invention can generally be measured with a DSC (differential scanning calorimeter), and appears as an endothermic peak. There are some materials with an amorphous structure that do not necessarily have a clearly defined melting point, but in this case, the generally known softening point is used as a substitute. This is because most of these materials exhibit endothermic peaks when measured using the DSC described above.

Further, the softening point can be determined using differential thermal analysis (DTA). The softening point is the temperature at which the slope of the DTA graph changes for the first time.

In the nonwoven fabric of the present invention, the 't'f1 synthetic fiber is extremely 1. ■It is mixed randomly in the fiber in the form of substantially single fibers. With such a mixed state, high strength can be achieved without substantially impairing the features of the ultrafine fibers described above. The mixing ratio (weight) of the mixed fibers to the total fiber amount is 20 to 80%, preferably 3
0-70%, especially 40-60% is preferred. If it is less than 20%, the thermal bonding strength will be low and it will be difficult to obtain sufficient strength. on the other hand,
If it exceeds 80%, the above-mentioned characteristics of the ultrafine fibers will be lost, which is not preferable.

In addition, ultrafine fibers are also randomly dispersed in the form of single fibers.
i is more preferable because the various performances described above are improved. Also,
The nonwoven fabric of the present invention may be a mixture of a third material, fibers with different fiber diameters, shapes, etc., powder, and the like.

In addition, since the ultrafine fibers obtained by the melt-blowing method have an extremely small fiber diameter, it is difficult to estimate the average length of the fibers, but it is 30 mm or more, and in many cases 100 to 100 mm.
Estimated to be 500mm.

The method for obtaining the ultrafine fiber nonwoven fabric of the present invention is not particularly limited, such as a melt blow method, a flash spinning method, a super draw method, or a combination of a composite fiber method and a paper making method, but the melt blow method is particularly preferred.

As a method for mixing mixed fibers, for example, in the Mel I blow method and the flash spinning method, a web of crimped short fibers is created, and this is made to fly through the ultrafine fiber group being spun using a Rickerin roll or the like. A method of mixing and obtaining a sheet-like product,
Alternatively, there is a method in which the crimped short fibers are made into slivers, defibrated and flung using a combing roll (roll-like material with many teeth), and mixed in the same manner as described above to obtain a sheet-like material. In addition, the short fibers to be mixed with the ultrafine fibers obtained by the super draw method or seabird fiber method are cut into 3 to 30 mm, preferably 5 to 10 mm, to create a slurry in which these two types are mixed, and sheets are made by the papermaking method. There is a way to do this. These polar 111 fiber sheets may be subjected to a -tan entanglement treatment.

Examples of the thermal bonding method include a hot embossing method, a hot Kangoo method, a hot air method, and an ultrasonic bonding method. In particular, the hot air bonding method is preferable because it can thermally bond the nonwoven fabric without pressurizing it, yielding a bulky nonwoven fabric and fully exhibiting the features of the ultrafine fibers described above. Thermal bonding temperature only needs to be higher than the temperature at which thermal bonding occurs. - For boat fishing? It is sufficient if it is above the softening point of the kongo fiber. On the other hand, if the content is higher than the melting point of the ultrafine fibers, the ultrafine fibers will be undesirably thermally bonded to each other. Therefore, in the present invention, it is preferable that the softening point of the mixed fiber is higher than the melting point of the ultrafine fiber.

The nonwoven fabric of the present invention can be subjected to various post-treatments. For example, it is possible to further improve the filter performance and dust suction power by converting it into an electret using a corona discharge method or the like.

〔Example〕

EXAMPLES The present invention will be explained in more detail with reference to Examples below.

The definitions and measurement methods of various physical properties shown in Examples and Comparative Examples are shown below.

◎Average fiber diameter (R1) Ten arbitrary points on the sample were examined using an electron microscope at a magnification of 2000.
Take 10 photos at double magnification. Measure the diameter of 10 arbitrary fibers for each photograph, and do this for each of the 10 photographs. A total of 100 fiber diameter measurements are obtained and the average value is calculated.

◎Thickness (mm) Measured using a peacock type thickness gauge under a constant load of 130 g/cfl.

◎Tensile strength (8/fabric weight) Take a 20mm width x 160mm length as a 2° sample.
Using a universal tensile test R (Tensilon), grip c io
.

Value, load capacity! it 10okg, tensile speed 100mm/
The value is measured in minutes per 1 coo ljl, unit basis weight (
1g/rd).

◎Tear Strength (g/Weight) Take a sample of 60 mm x 65 mm in length, stop one sample on the sample stand, and make a cut with a knife. Read the maximum vibration using an Elmendorf tear tester. This value was converted per unit date (Ig/rrr).

◎Collection efficiency (%), pressure 1n loss (mm It z O)
Using a particle counter manufactured by K Company (model Kc-01B) on the Rion, use the atmospheric suction method to target dust particles of 0.3 and 1 or more under the conditions of suction air ff10.5ffi/min [
Established.

(2) Tilj Collection Efficiency The number of particles with and without sample (blank) is read with a vertile counter and calculated using the following formula.

■Pressure loss Read the differential pressure before and after the sample with a differential pressure gauge.

◎Crimp ratio (%) This is calculated by dividing the difference between the uncrimped length and the crimped length of the fiber by the crimped length.

◎Mixing ratio (%) The weight of the mixed fibers was divided by the weight of the nonwoven fabric and multiplied by 100 (directly).

Polypropylene was spun using a melt blow method to obtain a group of ultrafine fibers with an average fiber diameter of 1.7. The melting point of this fiber is D
When measured by SC, the temperature was 158°C. Thin diameter 25cm,
Polyethylene, length 64wn, crimp rate 40%, (melting point 1
(32° C.) was made into a sliver, and while a large number of these slivers were defibrated with a combing roll, the short fibers were made to fly and mixed into the ultrafine fiber group at the tip. This mixed fiber group is collected on the moving net surface provided below, and 20cm11
I got Notsu Lp. This web had no lumps of crimped short fibers, and was substantially dispersed in the form of single fibers, which were random and uniform. The mixing ratio of crimped short fibers was 50%.

This web was thermally bonded by passing through a medium 30 cm heat embossing roll with a diagonal (45") grid-like pattern. At this time, the temperature of the heat roll was 130°C, and the press pressure was 1
0 kg/c+MG, processing speed was 6 m/min.

Table 1 shows the properties (1) and physical properties of this nonwoven fabric. As a comparison,
A thermally bonded nonwoven fabric made only of ultrafine fibers without mixing crimped short fibers (
Comparative product 1), and a nonwoven fabric (comparative product 2) obtained in exactly the same manner as described in Example 1, except that polyethylene terephthalate single fibers were used as the crimped short fibers to be kneaded.
The values are also shown in Table 1.

Table 1 As is clear from this table, the strength of the product of the present invention was significantly improved and it was possible to use it alone. What's more, it was surprisingly found that the filter performance was improved, and it also had excellent oil absorption.

↓Jiru is made by spinning polyethylene terephthalate using the melt-blowing method to create an average fiber diameter of 2. The ultrafine fiber group of Otnh was used.

The melting point of this fiber was 258°C. Diameter 16 (4d)
), length 30 m, ) Copolyester fibers with various melting points (random copolyester using diethylene glycol as the third component for terephthalic acid and polyethylene) with a scanning line rate of 50% were made into 1.5 m fibers using a card method. This sheet is made into a wide sheet, defibrated with a Rickerin roll, and mixed uniformly into Hisou Ultrafine Fiber Y, which is then transferred and processed.
This fiber group was collected on the net surface of the
A web was obtained which was heated with warm air in the fundum of l. 1 scan shortened fiber ￥1
F's? The IL rate was 70%.

This web was thermally bonded using hot air.

Table 2 shows the physical properties of the obtained nonwoven fabric (fabric weight: 100 g/n).

A nonwoven fabric was obtained in exactly the same manner as in Example 1 except that the margin surface fiber diameter was set to the 9 side.

The basis weight of this nonwoven fabric is 65g/nf, and the thickness is 0.28mm.
The tensile strength is 8.6g/date, and the tearing strength is 2.
It was difficult to use alone due to its low basis weight of 7 g/fabric weight.

As is clear from this table, when the melting point difference between the extra ta fiber and the mixed polyester fiber is 20 to 200''C, an excellent sheet-like product can be obtained that satisfies both strength and filter performance at the same time.

Comparison of Polyethylene Fibers Mixed in Example 1 [Effects of the Invention] The nonwoven fabric of the present invention has excellent features of ultrafine fiber nonwoven fabrics such as filter performance, bacterial barrier properties, dust absorption, liquid absorption, and heat insulation. On the contrary, it is possible to improve the properties with almost no loss, and the strength is significantly improved, so it can be used alone without reinforcing it by pasting it with other high-strength sheets. becomes possible. For this reason, we use not only various filters, wipers, wraps, and insulation materials, but also civil engineering materials such as roofing materials, wall materials, surgical gowns, and sheets! It can now be widely used as medical and sanitary materials such as diapers, napkins, etc. Moreover, it is advantageous in terms of process since it does not require pasting other sheet-like materials, etc., and therefore it is excellent in terms of cost, and the industrial significance of this invention is great.

Claims (1)

[Claims] A sheet-like material in which ultrafine fibers with an average fiber diameter of 0.1 to 8.0 μm and fibers with an average fiber diameter of 10 μm or more are randomly mixed, the thick fibers being heated at a temperature of 10 to 200°C above the melting point of the ultrafine fibers. It is a thermoplastic fiber with a low melting point,
and a high-strength sheet-like article in which at least the low melting point thermoplastic fibers and the ultrafine fibers are partially thermally bonded.