JP6911098B2 - Closure for communication cable - Google Patents

Description

The present invention relates to a communication cable closure used for a communication cable such as an optical cable or a metal cable, and in particular, a communication cable closure having good watertightness and capable of preventing the inflow of water from the outside to the inside. Regarding.

Generally, connection portions and branch portions of communication cables such as optical cables and metal cables are protected by watertight closures (housings).
The communication cable closure has a sleeve that covers the core wire connection part of the communication cable and the fixing part of the communication cable, and an end face plate that is arranged at the end of the sleeve and has an insertion hole for inserting the communication cable inside. , In the sleeve, in the end face plate, between the sleeve and the end face plate, or a sealing member for filling a gap generated in a combination thereof.

17 (A) to 17 (C) are exploded perspective views showing a configuration example of a conventional communication cable closure.

FIG. 17A shows a configuration example of a communication cable closure used as the No. 7 subscriber optical standard closure (7SC) (hereinafter referred to as Conventional Example 1) (see, for example, Patent Document 1).

In the communication cable closure 100 of the conventional example 1, the closure 100 is divided into a plurality of sleeves 101 and 102 (two in this example), and a sealing member (first) is used to fill a gap between the divided sleeves 101 and 102. A rod-shaped gasket 103, which is a sealing member of 1), is installed.

Further, a port portion 105 which is a sealing member (second sealing member) is installed in order to fill a gap between the insertion hole 104a of the end face plate 104 provided at both ends of the sleeves 101 and 102 and the communication cable.

FIG. 17B shows a configuration example of a communication cable closure used as an underground optical closure (TN) (hereinafter referred to as Conventional Example 2) (see, for example, Patent Document 2).

In the communication cable closure 200 of the conventional example 2, the closure 200 is divided into a plurality of sleeves 201 and 202 (two in this example), and a sealing member (first) is used to fill a gap between the divided sleeves 201 and 202. A frame-shaped gasket 203, which is a seal member of 1), is installed.

Further, a port portion 205, which is a sealing member (second sealing member), is installed to fill a gap between the insertion hole 204a of the end face plate 204 provided at both ends of the sleeves 201 and 202 and the communication cable.

FIG. 17C shows a configuration example of a communication cable closure used as a closure (UP) installed vertically (hereinafter referred to as Conventional Example 3) (see, for example, Patent Document 3).
In the communication cable closure 300 of the conventional example 3, the end face plate 300b in which the communication cable insertion hole 300a is formed is arranged at one end of one sleeve 301 to be vertically placed, and the end face plate 300b and the sleeve 301 are arranged. A frame-shaped gasket 302 that is a sealing member (third sealing member) for filling the gap between the two is installed.

Further, a port portion 303 which is a sealing member (second sealing member) is installed in order to fill a gap between the insertion hole 300a of the end face plate 300b provided at the lower end portion of the sleeve 301 and the communication cable.

In the conventional closure for communication cables, in order to further improve the watertightness, a technique of forming an elastic material containing a water-absorbent polymer as a sealing member such as a gasket has been proposed (see Patent Documents 4 and 5 below. , Conventional example 4).

In Conventional Example 4, since the seal member is made of an elastic material containing a water-absorbent polymer, the seal member expands due to water absorption, and even if the sleeve, end face plate, communication cable, etc. are scratched, foreign matter, or dented. It is said that it can enter the gap and maintain watertightness.
Japanese Unexamined Patent Publication No. 9-135526 Japanese Patent No. 5354423 Japanese Unexamined Patent Publication No. 2013-113891 Japanese Unexamined Patent Publication No. 2008-15382 Japanese Unexamined Patent Publication No. 2008-3332

Gasket 103, which is the first sealing member of Conventional Example 1, and port portion 105, which is the second sealing member, gasket 203, which is the first sealing member of Conventional Example 2, and port portion 205, which is the second sealing member. The gasket 302, which is the third sealing member of Conventional Example 3, and the port portion 303, which is the second sealing member, are made of an elastic body made of, for example, rubber, an elastomer, or the like.

However, if there are scratches, foreign substances, or dents on the sleeve, end face plate, communication cable, etc., there is a problem that it is difficult for water to flow into the inside through the gaps and maintain watertightness.

In Conventional Example 4, the layer containing the water-absorbing polymer is connected to the inside of the closure, and the water-absorbing polymer has both a water-absorbing action and a moisture-releasing action in a lower humidity environment. Moisture penetrates into the closure and the humidity inside the closure rises.

Therefore, when the environmental temperature of the closure is lowered and the amount of water vapor in the closure exceeds the saturated amount of water vapor, there is a problem that dew condensation occurs in the closure.

In particular, in the case of a metal cable, there is a problem that the insulation resistance deteriorates due to this dew condensation and the communication quality deteriorates.

Further, the optical fiber cable also has a problem that the strength of the optical fiber is lowered due to contact with water.

The present invention has been made to solve the above problems, and to provide a closure for a communication cable which has good watertightness and can prevent the inflow of water from the outside to the inside. The purpose.

The communication cable closure of the present invention has a sleeve that covers the core wire connection portion of the communication cable and the fixing portion of the communication cable, and an insertion hole that is arranged at the end of the sleeve and for inserting the communication cable inside. In a communication cable closure having a provided end face plate and a sealing member in the sleeve, in the end face plate, between the sleeve and the end face plate, or a combination thereof.
The sealing member has a multi-layer structure from the inside to the outside, a first layer made of an elastic body containing no water-absorbing polymer is arranged in the innermost layer, and a water-absorbing polymer is placed in at least one layer other than the innermost layer. A second layer of the containing elastic body is arranged.
It is characterized by that.

The end face plate may be arranged at one end of the sleeve.
The end face plate may be arranged at one end and the other end of the sleeve.
The sleeve is divided into a plurality of parts, and the sealing member may have a first sealing member for filling a gap between the divided sleeves.
The sealing member may have a second sealing member for filling a gap between the insertion hole of the end face plate and the communication cable.
The sealing member may have a third sealing member for filling the gap between the sleeve and the end face plate.
The first layer may be a coating layer.
The coating layer may be coated with unvulcanized rubber.
The sealing member is composed of a second layer made of an elastic body containing a water-absorbing polymer, and a first layer made of an elastic body not containing a water-absorbing polymer, which is arranged inside and outside the second layer. It may have a layered structure.
The first layer may be a coating layer.
The coating layer may be coated with unvulcanized rubber.

According to the communication cable closure of the present invention, the following effects are obtained.
(1) Since a second layer made of an elastic body containing a water-absorbing polymer is arranged in at least one layer other than the innermost layer, the entire sealing member expands due to water absorption, and the sleeve, end face plate, and communication cable Even if there are scratches, foreign substances, or dents on the surface, it can enter the gap and maintain watertightness.
(2) Since the first layer made of an elastic body containing no water-absorbing polymer is arranged in the innermost layer, the inflow of external moisture into the closure and the moisture released from the absorbed second layer. It is possible to suppress the inflow (moisture permeation) into the closure of the closure and prevent the inflow of water from the outside to the inside. As a result, it is possible to prevent deterioration in quality and strength of the communication cable due to dew condensation and the like.

It is sectional drawing which shows schematic the seal member in the closure for communication cable which concerns on 1st Embodiment of this invention. It is sectional drawing which shows schematic the seal member in the closure for communication cable which concerns on 2nd Embodiment of this invention. It is sectional drawing which shows schematic the seal member in the closure for communication cable which concerns on 3rd Embodiment of this invention. It is sectional drawing which shows schematic the seal member in the closure for communication cable which concerns on 4th Embodiment of this invention. It is sectional drawing which shows schematic the seal member in the closure for communication cable which concerns on 5th Embodiment of this invention. It is sectional drawing which shows schematic the seal member in the closure for communication cable which concerns on 6th Embodiment of this invention. It is sectional drawing which shows schematic the seal member in the closure for communication cable which concerns on 7th Embodiment of this invention. It is sectional drawing which shows schematic the seal member in the closure for communication cable which concerns on 8th Embodiment of this invention. It is sectional drawing which shows typically the seal member in the closure for communication cable which concerns on 9th Embodiment of this invention. It is sectional drawing which shows typically the seal member in the closure for communication cable which concerns on the 10th Embodiment of this invention. (A) and (B) are cross-sectional views showing a procedure for inserting a communication cable into a seal member in a closure for a communication cable according to an embodiment of the ninth to tenth embodiments of the present invention. (A) to (C) are perspective views for explaining the joining procedure between layers of the sealing member. (A) is a perspective view showing a seal member, and (B) is a sectional view taken along line BB of (A). (A) to (E) are perspective views showing an example of a manufacturing process of the first layer and the second layer. (A) to (E) are perspective views showing an example of a manufacturing process of a seal member. (A) is a graph showing time on the horizontal axis, vertical axis showing the rate of change in water absorption period and drainage period at each coding thickness, (B) is time on the horizontal axis, and vertical axis is water absorption period and drainage period at each coding thickness. It is a graph which shows the weight change rate of. (A) to (C) are exploded perspective views showing the configuration of a conventional communication cable closure.

Hereinafter, embodiments of the present invention will be described.
Here, the communication cable closure according to each embodiment of the present invention is an improved seal member, and other members and configurations are the same as those of the conventional communication cable closure.

That is, the sealing member is used to fill the gap created in the sleeve, in the end face plate, between the sleeve and the end face plate, or a combination thereof.

The end face plates may be located at one end of the sleeve (see FIG. 17 (C)) or at one and the other end of the sleeve (FIGS. 17 (A), (B)). )reference).

When the sleeve is divided into a plurality of parts, the sealing member may have a first sealing member for filling the gap between the divided sleeves (see FIGS. 17A and 17B).
Further, the seal member may have a second seal member for filling the gap between the insertion hole of the end face plate and the communication cable (see FIGS. 17A and 17B).
Further, the sealing member may have a third sealing member for filling the gap between the sleeve and the end face plate (see FIG. 17C).

FIG. 1 is a cross-sectional view schematically showing a sealing member in a communication cable closure according to a first embodiment of the present invention.

As shown in FIG. 1, the seal member 1 of the communication cable closure according to the first embodiment of the present invention has a multi-layer structure from the inside to the outside, and the innermost layer is an elastic body containing no water-absorbing polymer. The first layer 2 made of the material is arranged, and the second layer 3 made of an elastic body containing a water-absorbing polymer is arranged in at least one layer other than the innermost layer. ..

The non-specific layer 4 other than the first layer 2 and the second layer 3 may be a layer made of an elastic body containing a water-absorbing polymer, or may be a layer made of an elastic body containing no water-absorbing polymer.

As the elastic body, for example, rubber, elastomer or the like is used.

Here, it is desirable that the elastic body containing no water-absorbing polymer has physical properties that can be expanded and contracted to such an extent that the elastic body containing the water-absorbing polymer does not prevent expansion due to water absorption.

Further, as the bonding between layers, for example, chemical bonding using an adhesive, mechanical bonding by fitting uneven portions, bonding using a mold, or the like is used.
According to the seal member 1 of the closure for a communication cable according to the first embodiment of the present invention, a second layer 3 made of an elastic body containing a water-absorbing polymer is arranged in at least one layer other than the innermost layer. Therefore, the entire sealing member expands due to water absorption, and even if there are scratches, foreign substances, or dents on the sleeve, end face plate, communication cable, etc., they can enter the gap and maintain watertightness.

Further, since the first layer 2 made of an elastic body containing no water-absorbing polymer is arranged in the innermost layer, external moisture flows into the closure and is discharged from the absorbed second layer 3. It is possible to suppress the inflow of water into the closure (moisture permeation) and prevent the inflow of water from the outside to the inside. As a result, it is possible to prevent deterioration in quality and strength of the communication cable due to dew condensation and the like.

FIG. 2 is a cross-sectional view schematically showing a sealing member in a communication cable closure according to a second embodiment of the present invention.
As shown in FIG. 2, the first layer 11 of the seal member 10 of the communication cable closure according to the second embodiment of the present invention is made of thin elastic rubber such as RTV (room temperature vulcanized type) silicone rubber. It is characterized by being a coated coating layer. Since it can be manufactured by coating, it can be manufactured inexpensively and easily. Other configurations are the same as those of the seal member 1.

FIG. 3 is a cross-sectional view schematically showing a sealing member in a communication cable closure according to a third embodiment of the present invention.
As shown in FIG. 3, the first layer 21 of the seal member 20 of the closure for a communication cable according to the third embodiment of the present invention is a coating layer coated with unvulcanized rubber. It is said.

As the unvulcanized rubber, unvulcanized butyl rubber or the like is used. Other configurations are the same as those of the seal member 1.

FIG. 4 is a cross-sectional view schematically showing a sealing member in a communication cable closure according to a fourth embodiment of the present invention.

As shown in FIG. 4, the seal member 30 of the communication cable closure according to the fourth embodiment of the present invention has a second layer 32 made of an elastic body containing a water-absorbing polymer and a second layer 32 thereof. It is characterized in that it has a three-layer structure composed of a first layer 31 made of an elastic body containing no water-absorbing polymer, which is arranged inside and outside the above.

The first layer 31 is a coating layer in which elastic rubber such as RTV (room temperature vulcanized type) silicone rubber is thinly applied.
According to the sealing member 30 of the fourth embodiment of the present invention, since the second layer 32 made of an elastic body containing a water-absorbing polymer is arranged in the intermediate portion, water is deeply infiltrated into the intermediate portion. The expansion action of the water-absorbing polymer can be exerted only when it occurs.

FIG. 5 is a cross-sectional view schematically showing a sealing member in a communication cable closure according to a fifth embodiment of the present invention.

As shown in FIG. 5, the first layer 41 of the seal member 40 of the communication cable closure according to the fifth embodiment of the present invention is a coating layer coated with unvulcanized rubber. It is a feature. Other configurations are the same as those of the seal member 30.
FIG. 6 is a cross-sectional view schematically showing a sealing member in a communication cable closure according to a sixth embodiment of the present invention.

As shown in FIG. 6, the seal member 50 of the communication cable closure according to the sixth embodiment of the present invention is a second seal member for filling a gap between the insertion hole 50a of the end face plate and the communication cable. It has a multi-layered structure from the inside to the outside, a first layer 51 made of an elastic body containing no water-absorbing polymer is arranged in the innermost layer, and at least one layer other than the innermost layer contains a water-absorbing polymer. It is characterized in that a second layer 52 made of an elastic body is arranged.

The non-specific layer 53 other than the first layer 51 and the second layer 52 may be a layer made of an elastic body containing a water-absorbing polymer or a layer made of an elastic body not containing a water-absorbing polymer.

As the elastic body, for example, rubber, elastomer or the like is used.

Here, it is desirable that the elastic body containing no water-absorbing polymer has physical properties that can be expanded and contracted to such an extent that the elastic body containing the water-absorbing polymer does not prevent expansion due to water absorption.

Further, as the bonding between the layers, for example, chemical bonding using an adhesive, mechanical bonding by fitting uneven portions, bonding using a mold, or the like is used.

According to the communication cable closure according to the sixth embodiment of the present invention, the second layer 52 made of an elastic body containing a water-absorbing polymer is arranged in at least one layer other than the innermost layer. The entire sealing member expands due to water absorption, and even if there are scratches, foreign substances, or dents on the end face plate, communication cable, etc., they can enter and maintain watertightness.

Further, since the first layer 51 made of an elastic body containing no water-absorbing polymer is arranged in the innermost layer, external moisture flows into the closure and is discharged from the absorbed second layer 52. It is possible to suppress the inflow of water into the closure (moisture permeation) and prevent the inflow of water from the outside to the inside. As a result, it is possible to prevent deterioration in quality and strength of the communication cable due to dew condensation and the like.

FIG. 7 is a cross-sectional view schematically showing a sealing member in a communication cable closure according to a seventh embodiment of the present invention.

As shown in FIG. 7, the first layer 61 of the seal member 60 of the communication cable closure according to the seventh embodiment of the present invention is made of thin elastic rubber such as RTV (room temperature vulcanized type) silicone rubber. It is characterized by being a coated coating layer. Other configurations are the same as those of the seal member 50.

FIG. 8 is a cross-sectional view schematically showing a sealing member in a communication cable closure according to an eighth embodiment of the present invention.

As shown in FIG. 8, the first layer 71 of the seal member 70 of the communication cable closure according to the eighth embodiment of the present invention is a coating layer coated with unvulcanized rubber. It is a feature. Other configurations are the same as those of the seal member 50.

FIG. 9 is a cross-sectional view schematically showing a sealing member in a communication cable closure according to a ninth embodiment of the present invention.

As shown in FIG. 9, the sealing member 80 of the communication cable closure according to the ninth embodiment of the present invention has a second layer 82 made of an elastic body containing a water-absorbing polymer and a second layer 82 thereof. It is characterized in that it has a three-layer structure composed of a first layer 81 made of an elastic body containing no water-absorbing polymer, which is arranged inside and outside the above.

The first layer 81 is a coating layer in which elastic rubber such as RTV (room temperature vulcanized type) silicone rubber is thinly applied.

According to the sealing member of the ninth embodiment of the present invention, since the second layer 82 made of an elastic body containing a water-absorbing polymer is arranged in the intermediate portion, deep water immersion occurs even inside the intermediate portion. Only when this is done, the expansion action of the water-absorbing polymer can be exerted.

FIG. 10 is a cross-sectional view schematically showing a sealing member in a communication cable closure according to a tenth embodiment of the present invention.

As shown in FIG. 10, the first layer 91 of the seal member 90 of the communication cable closure according to the tenth embodiment of the present invention is a coating layer coated with unvulcanized rubber. It is a feature. Other configurations are the same as those of the seal member 80.

11 (A) and 11 (B) are cross-sectional views showing a procedure for inserting a communication cable into a seal member in a closure for a communication cable according to a ninth to tenth embodiment of the present invention.

As shown in FIG. 11A, before the communication cable 92 is inserted into the insertion hole 50a of the end face plate formed in the seal member 90, the insertion hole 50a is closed by the coating layer 91a, and FIG. As shown in B), the communication cable 92 may be inserted into the insertion hole 50a by inserting the end portion of the communication cable 92 and breaking the coating layer 91a.

By closing the insertion hole 50a with the coating layer 91a before inserting the communication cable 92, it is possible to prevent the space of the insertion hole 50a from being narrowed due to the expansion of the elastic body due to water absorption, which makes it difficult to insert the communication cable 92. can do.

For joining the layers of the sealing member, for example, chemical joining using an adhesive is used, but joining using a mold may also be used.

12 (A) to 12 (C) are perspective views for explaining a procedure for joining layers of the sealing member.
First, as shown in FIG. 12A, a frame-shaped first layer 93b made of an elastic body containing no water-absorbing polymer is formed by the first mold 93a.

Next, as shown in FIG. 12B, the first layer 93b is installed in the second mold 93c.
Then, as shown in FIG. 12C, an elastic material containing a water-absorbing polymer is poured between the second mold 93c and the first layer 93b, and the second layer 93d is transferred to the first layer 93b. Join to.
As the joining of the seal members, joining by fitting unevenness may be used.

13 (A) is a perspective view showing a seal member, and (B) is a sectional view taken along line BB of (A).
In the sealing member 94 shown in FIG. 13A, a frame-shaped second layer 94b made of an elastic body containing a water-absorbing polymer is joined to the outside of a frame-shaped first layer 94a made of an elastic body containing no water-absorbing polymer. is doing. As shown in FIG. 13B, the convex portion of the first layer 94a and the concave portion of the second layer 94b are fitted and mechanically joined.

14 (A) to 14 (E) are perspective views showing an example of a manufacturing process of the first layer and the second layer.
An elastic material containing no water-absorbing polymer is poured between the upper mold 95a and the lower mold 95b (see FIG. 14 (A)) to form a rod-shaped first layer 95c having a convex portion.
Further, an elastic material containing a water-absorbing polymer is poured between the upper mold 95d and the lower mold 95e (see FIG. 14C) to form a rod-shaped second layer 95f having a recess.

Then, the convex portion of the first layer 95c and the concave portion of the second layer 95f are mechanically joined by fitting (see FIG. 14 (E)).

15 (A) to 15 (E) are perspective views showing an example of a manufacturing process of the seal member.
First, the masking tape 96b is attached only to the portion where the water-absorbing polymer surface is to be exposed on the surface of the elastic body 96a containing the water-absorbing polymer (see FIG. 15 (A)).

Then, it is immersed in a liquid unvulcanized rubber tank 96d for a predetermined time (see FIG. 15B).
Next, the surface of the elastic body 96a containing the water-absorbing polymer taken out from the unvulcanized rubber tank 96d and dried is coated with the unvulcanized rubber coating layer 96e (see FIG. 15C).

Then, by peeling off the masking tape 96b (see FIG. 15 (D)), a portion of the elastic body containing the water-absorbing polymer can be exposed at the portion where the masking tape 96b is attached (see FIG. 15 (E)). This manufacturing method of the sealing member makes it possible to easily and inexpensively manufacture a multi-layered sealing member.

16 (A) is a graph showing time on the horizontal axis, vertical axis showing the rate of change in water absorption period and drainage period at each coding thickness, (B) is time on the horizontal axis, vertical axis is water absorption period at each coding thickness and It is a graph which shows the weight change rate of the drainage period.

The present inventor conducted an experiment on the thickness change rate and the weight change rate of the water absorption period and the drainage period at each coding thickness.

Here, as the sample, a 15 mm * 30 mm * 3.5 mm water-absorbing expansion rubber was used, and a sample without coating and a sample with a coating layer of 0.02 / 0.04 / 0.08 / 0.2 mm on the surface were used. Created and prepared.
When the initial thickness and mass were set to 100%, the ratio of the thickness and mass change in 6 days of submersion and 5 days of natural drying after submersion was measured and graphed (see FIGS. 16A and 16B). ..

From this experiment, it was confirmed that there is a water absorption suppressing effect at any coating thickness, but it was found that when the coating is thin of 0.1 mm or less, the suppressing effect is not greater than when it is not coated. rice field.

On the contrary, if the coating is further thickened from 0.2 mm, it can be estimated that the effect of suppression is further enhanced, but in order to make it thicker, it is necessary to increase the number of coatings, and the suppression effect obtained as 0.2 mm or more with respect to the manufacturing cost. Turned out to be scarce.

Therefore, it was found that it is desirable that the coat thickness be about 0.1 mm to 0.3 mm.
The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the technical matters described in the claims.

The closure for a communication cable of the present invention is used to improve the watertightness of a connection portion or a branch portion of a communication cable such as an optical cable or a metal cable.

1: Sealing member 2: First layer 3: Second layer 4: Non-specific layer 10: Sealing member 11: First layer 20: Sealing member 21: First layer 30: Sealing member 31: First Layer 32: Second layer 40: Sealing member 41: First layer 50: Sealing member 50a: Insertion hole 51: First layer 52: Second layer 60: Sealing member 61: First layer 70: Seal Member 71: First layer 80: Sealing member 81: First layer 82: Second layer 90: Sealing member 91: First layer

Claims (11)

A sleeve that covers the core wire connection portion of the communication cable and the fixing portion of the communication cable, an end face plate that is arranged at the end of the sleeve and has an insertion hole for inserting the communication cable inside, and the inside of the sleeve. In a communication cable closure having a sealing member in the end face plate, between the sleeve and the end face plate, or a sealing member for filling a gap formed in a combination thereof.
The sealing member has a multi-layer structure from the inside to the outside, a first layer made of an elastic body containing no water-absorbing polymer is arranged in the innermost layer, and a water-absorbing polymer is placed in at least one layer other than the innermost layer. A second layer of elastic material containing is arranged,
A closure for communication cables that features this. The closure for a communication cable according to claim 1, wherein the end face plate is arranged at one end of the sleeve. The closure for a communication cable according to claim 1, wherein the end face plate is arranged at one end and the other end of the sleeve. The sleeve is divided into a plurality of pieces.
The sealing member has a first sealing member for filling the gap between the divided sleeves.
The closure for a communication cable according to any one of claims 1 to 3, wherein the closure is for a communication cable. The sealing member has a second sealing member for filling a gap between the insertion hole of the end face plate and the communication cable.
The closure for a communication cable according to claim 1 to 3. The sealing member has a third sealing member for filling the gap between the sleeve and the end face plate.
The closure for a communication cable according to claim 1 to 3. The closure for a communication cable according to any one of claims 1 to 6, wherein the first layer is a coating layer. The closure for a communication cable according to claim 7, wherein the coating layer is coated with unvulcanized rubber. The sealing member is composed of a second layer made of an elastic body containing a water-absorbing polymer, and a first layer made of an elastic body not containing a water-absorbing polymer, which is arranged inside and outside the second layer. The closure for a communication cable according to any one of claims 1 to 6, wherein the closure has a layered structure. The closure for a communication cable according to claim 9, wherein the first layer is a coating layer. The closure for a communication cable according to claim 10, wherein the coating layer is coated with unvulcanized rubber.

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