JP3440303B2 - Core for safety shoes made of fiber reinforced thermoplastic resin and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanically excellent toe core for safety shoes obtained by molding a fiber reinforced thermoplastic resin composite material, and a method for producing the same.

[0002]

2. Description of the Related Art Toecaps for safety shoes improve the strength and rigidity from the instep of the shoe to the tip of the shoe, and are considered important for protecting the feet from falling heavy objects. Conventionally, steel has been put into practical use as the material thereof, but since the weight of the shoe is large, the workability of the wearer is poor, and the weight reduction has been performed by the fiber reinforced resin composite material.

Fiber-reinforced resin composite materials include a composite material using a thermosetting resin as a resin and a composite material using a thermoplastic resin. The former is a fiber-reinforced thermosetting resin composite material for safety shoes. In the case of a core, it is brittle, cracks easily occur in the matrix, and there is a risk that the original impact strength cannot be expressed when a heavy object falls. On the other hand, in the case of the latter toecap for safety shoes made of fiber reinforced thermoplastic resin composite material, cracks are less likely to occur in the matrix, so the above danger can be avoided and the original impact strength can be sufficiently expressed. is there.

As toecaps for safety shoes made of these fiber-reinforced resin composite materials, reinforcing fibers such as glass fibers are woven, braided,
2. Description of the Related Art Toecaps for safety shoes and the like have been proposed in which a fiber-reinforced resin composite material obtained by forming a knitted fabric or a non-woven fabric into a composite with a thermosetting resin or a thermoplastic resin is formed by press molding or the like. For example, in Japanese Utility Model Laid-Open No. 59-162003, in a toecap of a safety shoe that is heated and pressure-molded with a base material in which long glass fibers are composited with a thermoplastic resin matrix, it is projected outward at the tip of the instep of the toecap. Composite toughened resin safety shoe toecap with thin wall formed by Mitsui Sho 62-64304.
JP-A No. 1994-242242 proposes a carbon fiber reinforced resin toecap made of a resin, which is formed by molding a fiber reinforced resin composed of a resin and a fiber reinforced material containing carbon fiber or carbon fiber.

However, the strength of these conventional toecaps for safety shoes made of fiber reinforced resin composite material cannot meet the standard of leather shoe safety shoes class L specified in JIST8101, and the strength is insufficient. It was

For this reason, Japanese Patent Laid-Open No. 05-147146 discloses a thermoplastic resin sheet reinforced by randomly arranging reinforcing fibers of about 12 mm to 100 mm and a thermoplastic resin sheet reinforced by reinforcing fibers such as woven fabric. -Toecaps for safety shoes, which are produced by heating and press-molding a molding sheet having a sandwich structure with a gut, have been proposed, but it takes time to stack them, and high molding pressure is required. However, there is a problem that the cost becomes high because of the use of.

[0007] As described above, the toe for a resin safety shoe, which can be easily molded under a low molding pressure, is lightweight, and has a strength that conforms to the safety shoe standard (JIS T8101 leather safety shoes L type), and its The actual manufacturing method has not been obtained yet.

[0008]

DISCLOSURE OF THE INVENTION The present inventors have obtained a composite material composed of a reinforcing fiber and a thermoplastic resin, and have a strength that conforms to safety shoe standards and can be easily molded at a low molding pressure. In order to obtain a toecap for safety shoes that can be manufactured, as a result of diligent study on the composition of the composite material and the molding method thereof, the composite material is prepared in two stages (tape material and sheet material). First, in the first step, a tape-shaped material having a degree of wetting of the reinforcing fiber by the thermoplastic resin of a certain value or more is manufactured, and then, using this tape-shaped material, a sheet-shaped composite material is manufactured. Then, when this sheet-shaped material is molded to manufacture a toecap for safety shoes, the reinforcing fibers are uniformly dispersed in the thermoplastic resin even if molding is performed at a low molding pressure, and as a result, it has excellent strength. Safety shoes It has been found that the toe can be obtained.

The present inventors have completed the present invention as a result of further repeated studies based on such findings.

[0010]

That is, the present invention relates to a toe core for safety shoes, characterized by being formed by molding a sheet material satisfying the following requirements A to D. The sheet-like material comprises reinforcing fibers and a thermoplastic resin, B. The volume content of the reinforcing fibers in the sheet material is 30.
% To 80%, C.I. The reinforcing fibers are substantially untwisted and have an average fiber length of 10 mm to 50 mm, D. A step in which the reinforcing fibers are uniformly dispersed in the thermoplastic resin, and a tape-shaped material made of the reinforcing fibers and the thermoplastic resin is produced and cut, and the cut tape-shaped material is uniformly dispersed and deposited. The present invention provides a method for manufacturing a toecap for safety shoes, which comprises a step of integrating the deposited tape-shaped materials to produce a sheet-shaped material and a step of press-molding the sheet-shaped material. .

The material of the thermoplastic resin in the sheet material used as the molding material of the toecap for safety shoes of the present invention is a polyamide resin represented by nylon 6, nylon 12, nylon 66, or polyethylene terephthalate. Polyester resin such as polyester and polybutylene terephthalate,
Polyolefin resins such as polyethylene and polypropylene, polyether ether ketone resins, polyphenylene sulfide resins, polyether ether resins, polycarbonate resins and the like, but are not particularly limited to these, and these 2 of thermoplastic resin
You may use it in combination of 2 or more types. The material of the thermoplastic resin is preferably selected according to the application of safety shoes, for example, polyolefin resin, etc. from the viewpoint of physical properties and price,
Nylon 12 or the like is preferably selected when moisture absorption resistance is required.

The reinforcing fiber in the sheet material used as the molding material of the toecap for safety shoes of the present invention includes inorganic fibers such as glass fiber and carbon fiber, organic fibers such as aramid fiber and polyethylene fiber, and , Metal fibers such as boron fiber and alumina fiber, but not limited to these, and two or more kinds of these reinforcing fibers may be used in combination. In addition, it is preferable to appropriately select the material of the reinforcing fiber depending on the application of the safety shoes. For example, when non-magnetic property is required, carbon fiber or the like is used, and when electrostatic property is required, metal fiber or the like is used. Although preferable, it is usually preferable to use glass fiber or the like in view of performance and cost.

The reinforcing fibers in the sheet material used as the molding material for the toecap for safety shoes of the present invention must be substantially twist-free. If the reinforcing fibers have twists, the strength and elastic modulus of the toecaps for safety shoes decrease, which is not preferable.

The length of the reinforcing fiber in the sheet material used as the molding material of the toecap for safety shoes of the present invention is 10 mm.
It is necessary to be 50 mm to 50 mm. When the length of the reinforcing fiber is shorter than 10 mm, the reinforcing efficiency of the toecap for safety shoes by the reinforcing fiber decreases, and when it is longer than 50 mm, it becomes difficult to uniformly disperse the reinforcing fiber in the thermoplastic resin. is there. The length of the reinforcing fiber is 15 mm to 45 mm.
mm is more preferable.

The reinforcing fibers in the sheet material used as the molding material for the toecap for safety shoes of the present invention must be uniformly dispersed in the thermoplastic resin. When a toe core for safety shoes is molded using a sheet-shaped material in which reinforcing fibers are not uniformly dispersed in the thermoplastic resin, the reinforcing fibers in the toe core for safety shoes will also be unevenly distributed, and the reinforcing fiber content will be low. This is because the strength of the portion becomes insufficient, and the strength of the portion having many reinforcing fibers is high, but conversely the elasticity is low, so that cracking is likely to occur. The state in which the reinforcing fibers are uniformly dispersed in the thermoplastic resin means a state in which the distribution state of the reinforcing fibers is uniform and the reinforcing fibers have no directionality. Here, if there is no unevenness in the distribution state of the reinforcing fibers, for example, a sheet-shaped material is cut into 5 or more parts in a size of 2 to 3 g, and JI
It means that the difference between the maximum value and the minimum value of the volume content measured according to SK7052 is within 3%. However, the above evaluation method is not particularly limited because it depends on the type of reinforcing fiber, and the distribution state may be substantially similar to the above. In addition, the state in which the reinforcing fibers have no direction,
When the sheet-shaped material is visually observed, it means that the longitudinal directions of most of the reinforcing fibers are non-parallel to each other.
Further, as a method for obtaining a state in which the reinforcing fibers are uniformly dispersed in the thermoplastic resin, for example, first, a tape-shaped material made of the reinforcing fibers and the thermoplastic resin is prepared, and the tape-shaped material is made to have a length of 10 to 50 mm. Examples of the method include cutting and flying the cut tape-shaped material with air or the like in a space such as a box, or stirring the material in a liquid fluid, and then depositing the material. The method is not limited.

The volume content of the reinforcing fibers in the sheet material used as the molding material of the toecap for safety shoes of the present invention is 3
It is necessary to be 0% to 80%. When the volume content is less than 30%, it is difficult to obtain the desired physical properties, and when the volume content exceeds 80%, the reinforcing fibers are likely to be exposed on the surface layer of the toecap for safety shoes, and its appearance may be impaired. This is because the property is high.

It is necessary that at least 70% of the total number of the reinforcing fibers in the tape-shaped material used in the method for manufacturing the toecap for safety shoes of the present invention is wet with the thermoplastic resin. When the content is 70% or less, the workability is impaired by the fluff of the reinforcing fibers when the sheet-like material is produced, the reinforcing fibers are exposed and the strength is reduced, and the sheet-like material is molded. This is because a high molding pressure and a long molding time are required in order to impregnate the reinforcing fiber with the thermoplastic resin when molding. The wet state here means a state in which 50% or more of the peripheral length of the reinforcing fiber is in contact with the resin in the cross section of the tape-shaped material arbitrarily selected. At least 70% of the total number of the reinforcing fibers is wet with the thermoplastic resin, that is, the wet reinforcing fibers with respect to the total number of the reinforcing fibers present in the cross section of the tape material arbitrarily selected. Is 70% or more.

In the method for producing a toecap for a safety shoe of the present invention, the method for producing a sheet-shaped material from a tape-shaped material is not particularly limited, but preferably a tape-shaped material composed of reinforcing fibers and a thermoplastic resin. Is prepared, cut into a predetermined length, and the cut tape-shaped material is uniformly dispersed and deposited, and then heated and pressed to at least a part of the thermoplastic resin constituting the tape-shaped material, preferably A sheet-shaped material is produced by melting the whole and solidifying by cooling. Examples of this integration method include a method of fixing a part or all of the tape-shaped material with a thermoplastic binder, an elastomer or the like, in addition to heating and pressurization, and particularly, these methods It is not limited to.

In the method for producing a toecap for a safety shoe according to the present invention, a method for producing a toecap for a safety shoe by press-molding a sheet-shaped material comprises heating the sheet-shaped material to obtain a thermoplastic resin. It is not particularly limited as long as it is melted and press-molded to obtain a toecap for safety shoes, but the molding pressure at the time of press-molding is 5 kgf / cm ^{2 to} 50 kgf / cm.
It is preferably in the range of ² . It is preferable that the molding pressure is in the above range as the press molding such as conventional hot stamping molding and high-speed compression molding. At that time, when the molding pressure is 5 kgf / cm ² or less, the material flow is This is because it is not completely performed, and it becomes difficult to uniformly disperse the reinforcing fibers, and the molding pressure is 50 kgf.
This is because when the value exceeds / cm ² , a large amount of burr is generated due to material flow. An appropriate molding pressure may be selected within the above range depending on the combination of the reinforcing fiber and the resin.

[0020]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. The results of evaluation of the cross-sectional state, physical properties and appearance of the sheet-like materials obtained in Reference Examples 1 to 6 are shown in Table 1 and Example 1
Table 2 shows the evaluation results of the glass fiber distribution state, static strength and impact strength of the toecaps for safety shoes obtained in Comparative Example 1
It was shown to.

Each evaluation was performed as follows.
The size of the sheet material used for the measurement is 250 mm × 250 mm in each case. As for the impregnation state of the sheet-shaped material, 5 sheets of the sheet-shaped material were used, and each of the 5 points of the corner (4 points) and the central portion (1 point) of each sheet-shaped material had a width of 20 mm and a length of 20 mm. 5 pieces of 20mm each, 2 in total
Of the reinforcing fibers observed in the cross section of each of the 5 samples, 50% or more of the peripheral length was in contact with the resin, and the average value of the content (%) of the reinforcing fibers was calculated. Is 95% or more, it is ◯, 75 to 95% is Δ, and less than 75% is x. For the voids of the sheet-shaped material, samples are taken in the same manner as above, and the average value of the number of voids with a diameter of 0.1 mm or more observed in the cross section of each sample is calculated per sheet, and the average value is 1 In the following cases, it was evaluated as ◯, and in the case of 2 to 10 as Δ. For the strength and elastic modulus of the sheet-shaped material, the bending strength and bending elastic modulus are measured by the method A of the bending test method (bending test method of glass fiber reinforced plastic) specified in JIS K 7055, and the average value is used as a reference. When the value was about the same as that of the sheet-shaped material obtained in Example 1, it was evaluated as ◯, when it was about half, it was evaluated as Δ, and when it was less than that, it was evaluated as x. The width of the sheet material is 250m
When visually observing the surfaces of five sheet-shaped materials each having a length of m and a length of 250 mm, the number of places where glass fibers were recognized to be exposed on the surface of the sheet-shaped molding material was calculated, and per sheet-shaped material When the average value of is 0, ○, 1
When there were three, it was marked with Δ, and when there were four or more, it was marked with x. The gloss of the surface of the sheet-shaped material was observed by visually observing the projected state of the white fluorescent lamp (18 watts) (the boundary state of the white fluorescent lamp reflected in the sheet-shaped molding material installed 1 m below the vertical direction), and Reference Example 1 Compared with the observation result of the sheet-shaped material obtained in step 1, the case was about the same, the case was about half, the case was Δ, and the case less than that, the case was x. Regarding the dispersion state of the reinforcing fibers in the sheet-shaped material, five sheet-shaped materials were used, and a total of 5 points of the corners (4 points) and the central portion (1 point) of each sheet-shaped material,
A total of 25 samples each having a width of 20 mm and a length of 20 mm were sampled at each point, and the difference (%) between the maximum value and the minimum value of the glass fiber volume content ratio (according to JIS K 7052) in each sample. Was measured, and the state of the glass fiber obtained from the soft X-ray photograph of the sheet-shaped material was also evaluated and comprehensively judged. When the average value of the measured values of the difference between the maximum value and the minimum value of the above-mentioned volume content is within 3% and the state of the glass fiber is good, it was marked with ◯, and in other cases, it was marked with x.

The time and effort required for forming the toe core for safety shoes were comprehensively determined by the time required to complete the installation of the molding material in the mold and the handling property of the molding material. The distribution state of the glass fibers in the toecaps for safety shoes is such that five toecaps for safety shoes are used, and the length is about 10 mm and the width is about 10 mm from any 5 positions of the toecaps for safety shoes.
A total of 25 rectangular samples were collected, and the volume content of glass fiber in each sample (according to JIS K7052)
The difference (%) between the maximum value and the minimum value of was measured, and when the average value of the difference was within 3%, it was marked with ◯, and when it exceeded 3%, it was marked with x. The static strength of the toecap for safety shoes can be measured by installing a compression jig on the load cell of an Instron type universal testing machine and setting a crosshead speed of 10
The toe core is pressed at mm / min, the maximum load value obtained at that time is measured, and compared with the measurement result of the molded product obtained in Example 1, if the results are the same, ○, if a little worse Is △, and when bad, it is ×. Impact strength of toecaps for safety shoes is ASTM
The drop impact test according to D3029 (method FB) was performed, the maximum impact load value obtained at that time was measured, and compared with the measurement result of the molded product obtained in Example 1, the same degree was obtained. The case was marked with ◯, the case of a little bad was marked with Δ, and the bad was marked with x.

Reference Example 1. Thickness consisting of glass fiber and polypropylene resin 0.1
mm, width 10 mm, tape-shaped material in which glass fiber is wetted by polypropylene resin by 70% (glass fiber volume content 45%, glass fiber arrangement direction: length direction of tape-shaped material) ) Is cut into an average length of 20 mm, which is randomly dispersed and accumulated in a mold to form a sheet-like material, which is press-molded at a molding temperature of 210 ° C. and a molding pressure of 10 kg.
A sheet-shaped molding material having a thickness of 3.5 mm was produced under the conditions of f / cm ² and a pressing time of 10 minutes.

Reference Example 2. The same tape-shaped material as in Reference Example 1 was cut into an average length of 5 mm, and press-molded under the same conditions as in Reference Example 1 to produce a sheet-shaped molding material having a thickness of 3.5 mm.

Reference Example 3. The same tape-shaped material as in Reference Example 1 was cut into an average length of 60 mm, and press-molded under the same conditions as in Reference Example 1 to produce a sheet-shaped molding material having a thickness of 3.5 mm.

Reference Example 4. A tape-shaped material similar to that of Reference Example 1 was cut to an average length of 20 mm except that the volume content was 15%, and press molding was performed under the same conditions as in Reference Example 1 to obtain a thickness of 3.5 mm.
The sheet-like molding material of was produced.

Reference Example 5. A tape-shaped material similar to that of Reference Example 1 was cut into an average length of 20 mm except that the volume content was 90%, and press molding was performed under the same conditions as in Reference Example 1 to obtain a thickness of 3.5 mm.
The sheet-like molding material of was produced.

Reference Example 6. A tape-shaped material similar to that of Reference Example 1 was cut to an average length of 20 mm except that the glass fiber was wet with polypropylene resin by 50%, and this was press-molded under the same conditions as in Reference Example 1. Then, a sheet-like molding material having a thickness of 3.5 mm was produced.

Example 1. The sheet-like material composed of glass fiber and polypropylene resin described in Reference Example 1 was cut into an appropriate size, heated to 220 ° C. with a far infrared heater, and then put into a mold set to a surface temperature of 60 ° C. It was installed and pressed at a molding pressure of 10 kgf / cm ² for 1 minute to obtain a toecap for safety shoes.

Comparative Example 1. The sheet-shaped molding material produced in Reference Example 3 in which the average length of the tape-shaped material was 60 mm was molded under the same conditions as in Example 1 to obtain a toecap for safety shoes.

Comparative Example 2. The sheet-shaped molding material produced in Reference Example 2 in which the average length of the tape-shaped material is 5 mm is molded under the same conditions as in Example 1,
I got a toecap for safety shoes.

Comparative Example 3. A surface temperature of a molding material (volume content of glass fiber: 45 vf%) obtained by impregnating a mat having an average length of glass fiber of 20 mm with an unsaturated polyester resin and then semi-curing
Installed in a mold set to 20 ℃, molding pressure 10kgf /
The pressure was applied at cm ² for 20 minutes to obtain a toecap for safety shoes.

Comparative Example 4. Twill fabric made of glass fiber (56 warps / inch, 26 wefts /
Surface temperature of prepreg (glass fiber content 45vf%) impregnated with unsaturated polyester resin
Ten layers were alternately placed in a mold set to 0 ° C. and the pressure was applied at a molding pressure of 10 kgf / cm ² for 20 minutes to obtain a toecap for safety shoes.

[0034]

[Table 1]

[0035]

[Table 2]

As described above, the present invention is significantly lighter than the conventional metal products, but JIS T8.
101-1987 Leather safety shoes Toecaps for safety shoes that have physical strengths that meet the specifications of Class L safety and have superior impact resistance compared to those made of thermosetting resin, and low pressure, and The present invention provides a method for easily manufacturing the toecap for a safety shoe. As described above, the toecap for a safety shoe of the present invention can be easily manufactured and has physical strength that complies with the resin toecap standard of the JIS leather shoe safety shoe, so that the manufacturing industry, the mining industry, the transportation industry, the freight handling The present invention is effective because it is useful for leather shoes and safety shoes used at work sites such as work and forestry, and can be applied to sports and leisure shoes.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-2-143810 (JP, A) JP-A-5-269002 (JP, A) Actually open 62-73706 (JP, U) Actually open 54- 171948 (JP, U) (58) Fields surveyed (Int.Cl. ⁷ , DB name) A43B 23/08-23/17 B29C 43/02 C08J 5/04

Claims (4)

(57) [Claims] 1. A toecap for a safety shoe, which is formed by molding a sheet material satisfying the following requirements A to D. A. The sheet-like material comprises reinforcing fibers and a thermoplastic resin, B. The volume content of the reinforcing fibers in the sheet material is 30.
% To 80%, C.I. The reinforcing fiber is substantially untwisted and its fiber length
Is 10 mm to 50 mm, and D. In the thermoplastic resin, the reinforcing fibers are
The distribution is uniform and the reinforcing fibers are dispersed with no orientation . 2. A toecap for a safety shoe, wherein the sheet-shaped material according to claim 1 is formed by cutting , accumulating, and integrating a tape-shaped material composed of a substantially non-twisted reinforcing fiber and a thermoplastic resin. . 3. The toecap for safety shoes according to claim 1, wherein at least 70% of the total number of the reinforcing fibers of the tape-shaped material according to claim 2 is wet with a thermoplastic resin. 4. A step of producing and cutting a tape-shaped material composed of reinforcing fibers and a thermoplastic resin, a step of uniformly and randomly dispersing and depositing the cut tape-shaped material, and the deposited tape-shaped material being integrated. A method for producing a toecap for safety shoes, comprising the steps of producing a sheet-shaped material and pressing the sheet-shaped material.