Fiber with core

Abstract

An optical fiber ribbon core (1) is a discontinuously connected type of optical fiber ribbon core (1) in which an adhesive portion (2) and a non-adhesive portion (3) are intermittently arranged in the longitudinal direction (L) between adjacent optical fiber cores (10) by adhesive resin. The adhesive portion (2) is disposed on one side of the optical fiber ribbon core (10). A portion of the adhesive portion (2) protrudes beyond the tangent (T) of the surface of the one side of the adjacent optical fiber core (10). In the longitudinal direction (L), the height of at least one of the longitudinal direction ends (2c, 2d) of the adhesive portion (2) is greater than that of the central part of the adhesive portion (2). The composite elastic modulus of the adhesive resin at 23°C is 0.5 GPa or more and 6.0 GPa or less.

Description

Technical Field

[0001] This disclosure relates to optical fiber ribbon core. This disclosure claims priority based on Japanese Patent Application No. 2020-210491, filed on December 18, 2020, and invokes all the contents described in that application. Background Technology

[0002] Patent Documents 1 and 2 disclose so-called discontinuously connected fiber ribbon cores. Patent Document 1 discloses a fiber ribbon core obtained by coating an adhesive component for bonding the fiber optic strands forming the fiber ribbon core with equal amounts on both the top and bottom sides of the fiber ribbon core. Furthermore, it discloses that by setting the thickness of the adhesive component of the fiber ribbon core to "thickness = (√3-1) / 2 × D (D is the diameter of the fiber optic strand)," contact between the fiber optic strands and the adhesive components of other fiber optic strands can be prevented when the fiber optic strands are packed at their densest density.

[0003] Patent Document 2 also discloses that the fiber ribbon core is coated with adhesive components on both the top and bottom sides of the fiber ribbon core. Furthermore, Patent Document 2 discloses that the thickness of a portion of the adhesive component is set such that it protrudes beyond the tangent to the surface of each single-core coated fiber, at least at its central portion.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2016-133607

[0007] Patent Document 2: Japanese Patent Application Publication No. 2016-146003 Summary of the Invention

[0008] One aspect of this disclosure relates to the fiber optic ribbon core.

[0009] An intermittently connected fiber ribbon core, wherein, among a portion or all of the multiple fiber ribbons arranged side-by-side along a width direction orthogonal to the longitudinal direction, adhesive portions formed by bonding between adjacent fiber ribbons and non-adhesive portions not bonded by the adhesive resin are intermittently provided in the longitudinal direction.

[0010] The adhesive portion is disposed on one side of the optical fiber ribbon core.

[0011] A portion of the adhesive portion protrudes beyond the tangent to the surface of the single-sided side of the adjacent optical fiber core.

[0012] In the longitudinal direction, the height of at least one of the longitudinal ends of the adhesive portion is greater than that of the central portion of the adhesive portion.

[0013] The adhesive resin has a composite elastic modulus of 0.5 GPa to 6.0 GPa at 23°C. Attached Figure Description

[0014] [ Figure 1 ] Figure 1 This is a schematic plan view showing an embodiment of an optical fiber ribbon core.

[0015] [ Figure 2 ] Figure 2 This is a schematic cross-sectional view of an optical fiber core involved in an implementation method.

[0016] [ Figure 3 ] Figure 3 This is a schematic cross-sectional view of the adhesive portion in the fiber ribbon core according to one embodiment.

[0017] [ Figure 4 ] Figure 4 This is a schematic side view of the adhesive portion in the fiber ribbon core according to an embodiment. Detailed Implementation

[0018] [The problem this disclosure aims to solve]

[0019] Patent Document 1 describes an optical fiber ribbon core with equal amounts of adhesive resin on both sides. Furthermore, the thickness of the adhesive resin is set to a level that prevents it from contacting other optical fiber elements. Therefore, when a force is applied during the installation of the optical cable to cause the optical fiber ribbon core to curl and bend in its cross-sectional direction, damage to the adhesive resin on the bent outer side or peeling of the adhesive resin from the optical fiber element is likely to occur. As a result, there is a possibility that the optical fiber elements may become loose.

[0020] In the fiber ribbon core described in Patent Document 2, since the thickness of the adhesive portion on one of the two sides of the fiber ribbon core is set to be at least as thick as the thickness protruding through the tangent of the surface of each single-core coated fiber, the cross-sectional area of ​​the fiber ribbon core increases, which becomes disadvantageous in terms of high-density optical cables.

[0021] The purpose of this disclosure is to suppress the increase in the cross-sectional area of ​​the fiber core while making it difficult to cause damage to the adhesive resin or peeling of the adhesive resin from the fiber core, thereby reducing the possibility of the fiber core becoming loose.

[0022] [The Effects of This Disclosure]

[0023] According to the configuration of this disclosure, the increase in the cross-sectional area of ​​the optical fiber core can be suppressed, while it is difficult to cause damage to the adhesive resin or peeling of the adhesive resin from the optical fiber core, thereby reducing the possibility of the optical fiber core becoming loose.

[0024] [Description of embodiments of this disclosure]

[0025] Implementation methods of this disclosure are listed and described.

[0026] One aspect of this disclosure relates to the fiber optic ribbon core.

[0027] An intermittently connected fiber ribbon core, wherein, among a portion or all of the multiple fiber ribbons arranged side-by-side along a width direction orthogonal to the longitudinal direction, adhesive portions formed by bonding between adjacent fiber ribbons and non-adhesive portions not bonded by the adhesive resin are intermittently provided in the longitudinal direction.

[0028] The adhesive portion is disposed on one side of the optical fiber ribbon core.

[0029] A portion of the adhesive portion protrudes beyond the tangent to the surface of the single-sided side of the adjacent optical fiber core.

[0030] In the longitudinal direction, the height of at least one of the longitudinal ends of the adhesive portion is greater than that of the central portion of the adhesive portion.

[0031] The adhesive resin has a composite elastic modulus of 0.5 GPa to 6.0 GPa at 23°C.

[0032] Typically, because the adhesive resin application is interrupted, the thickness of the adhesive resin at the longitudinal end of the adhesive portion in the longitudinal direction is thinner than that at the center of the adhesive portion in the longitudinal direction. This makes it easy for the adhesive portion to break or peel off from the longitudinal end, where stress tends to concentrate. In the above configuration, since at least one of the longitudinal ends of the adhesive portion is thicker than the center of the adhesive portion in the longitudinal direction, breakage or peeling of the adhesive portion from that longitudinal end can be suppressed, thereby reducing the possibility of fiber core loosening. Furthermore, since the composite elastic modulus of the adhesive resin is 0.5 GPa or higher, it is more difficult for the adhesive resin to break, and since the composite elastic modulus is set to 6.0 GPa or lower, transmission loss at low temperatures can be suppressed. Additionally, since the adhesive resin is applied only to one side of the fiber ribbon core, the increase in the cross-sectional area of ​​the fiber ribbon core can be suppressed, thereby contributing to high-density optical cables.

[0033] In the fiber ribbon core.

[0034] The tear force when tearing the adhesive portion, as determined by the tear test specified in JIS C 6838:2019, is preferably 0.005 N or more and 0.200 N or less.

[0035] According to this configuration, since the tear force of the adhesive portion is set to 0.005N or more, it is less likely to cause damage to the adhesive resin, thereby further reducing the possibility of fiber core loosening. Furthermore, since the tear force of the adhesive portion is set to 0.200N or less, adhesive resin is less likely to remain on the fiber core when the operator tears the adhesive portion, thus suppressing any reduction in operability in subsequent processes such as the insertion of the fiber core into the protective tube.

[0036] In the fiber ribbon core.

[0037] The maximum value of the height of the protrusion of the adhesive portion from the tangent is preferably 10 μm or more and 100 μm or less.

[0038] According to this configuration, by setting the maximum protrusion height to 10 μm or more, the amount of adhesive resin used and the cross-sectional area of ​​the adhesive resin are increased, thus enabling a more secure bond between adjacent fiber cores. As a result, it is less likely for the adhesive resin to be damaged by external forces, thereby further reducing the possibility of fiber core loosening. In addition, by setting the maximum protrusion height to 100 μm or less, the degradation of transmission loss at low temperatures can be suppressed.

[0039] In the fiber ribbon core.

[0040] Preferably, in the width direction, each of the width-direction ends of the adhesive portion is located further outward than the center of the respective adjacent optical fiber core.

[0041] According to this configuration, since a sufficient amount of adhesive resin is used and the contact area between the adhesive resin and the optical fiber core is increased in the width direction, it is more difficult for the adhesive resin to be damaged or for the adhesive resin to peel off from the optical fiber core, thereby further reducing the possibility of the optical fiber core becoming loose.

[0042] [Details of the embodiments disclosed herein]

[0043] Hereinafter, examples of embodiments related to this disclosure will be described with reference to the accompanying drawings. It should be noted that in the following description, even in different drawings, the same or equivalent elements are labeled with the same symbols, and repeated descriptions are appropriately omitted. Furthermore, in the drawings used in the following description, the scale has been appropriately changed to make the components identifiable.

[0044] First, use Figure 1 and Figure 2 The present disclosure provides a general description of the optical fiber ribbon core 1 and the optical fiber core 10 contained therein. Figure 1This is a schematic plan view showing the fiber optic ribbon core 1 according to this embodiment. The fiber optic ribbon core 1 includes multiple (12 in this example) fiber optic cores 10 (including 10A and 10B). The multiple fiber optic cores 10 are arranged side by side in the width direction W orthogonal to the longitudinal direction L. The fiber optic ribbon core 1 is an intermittently connected type of fiber optic ribbon core, wherein adhesive portions 2 formed by bonding adjacent fiber optic cores 10 with adhesive resin and non-adhesive portions 3 not bonded by adhesive resin between adjacent fiber optic cores 10 are intermittently arranged along the longitudinal direction L.

[0045] It should be noted that, in Figure 1 In the illustrated fiber optic ribbon core 1, each individual single-core fiber optic core 10 is bonded together in pairs using adhesive resin, but this is not a limitation; it can also be bonded together in groups of three or more. Alternatively, the fiber optic ribbon core 1 can be formed by using multiple fiber optic cores that are assembled from multiple single-core fiber optic cores 10 and integrally coated with a coating resin and connected together. Furthermore, the intermittently provided bonding portions 2 and non-bonding portions 3 can be between a portion of the fiber optic cores 10 or between all of the fiber optic cores 10.

[0046] Figure 2 This is a schematic cross-sectional view of the optical fiber core 10 according to this embodiment. Specifically, Figure 2 It is Figure 1 The illustrated fiber core 10 is a schematic cross-sectional view when it is cut in a plane that includes the thickness direction perpendicular to the longitudinal direction L and the width direction W.

[0047] Figure 2 The optical fiber core 10 shown includes an optical fiber 11, a primary resin layer 12, a secondary resin layer 13, and a colored resin layer 14. There is no particular limitation on the outer diameter of the optical fiber core 10; for example, it can be around 200 μm, or larger, or smaller.

[0048] Optical fiber 11 includes a core and a cladding. Optical fiber 11 is, for example, glass fiber. A primary resin layer 12 covers the outer periphery of optical fiber 11. The primary resin layer 12 is formed, for example, of a soft UV-curable resin with a low Young's modulus. A secondary resin layer 13 covers the outer periphery of the primary resin layer 12. The secondary resin layer 13 is formed, for example, of a hard UV-curable resin with a high Young's modulus. A colored resin layer 14 covers the outer periphery of the secondary resin layer 13. The colored resin layer 14 is a layer used to improve the identification of the optical fiber core 10, and is formed, for example, of a colored UV-curable resin.

[0049] Next, use Figure 3 and Figure 4 The adhesive portion 2 in the fiber optic ribbon core 1 will be described in detail. Figure 3 This is a schematic cross-sectional view of the adhesive portion 2 in the optical fiber ribbon core 1 according to this embodiment. Specifically, Figure 3 It is Figure 1 The diagram shows a schematic cross-sectional view of optical fiber cores 10A and 10B, and the adhesive portion 2 formed between optical fiber cores 10A and 10B, cut in a plane including the aforementioned thickness direction. It should be noted that... Figure 3 In the diagram, the layers contained in fiber cores 10A and 10B are omitted.

[0050] The adhesive portion 2 is formed by curing the adhesive resin. There are no particular restrictions on the type of adhesive resin as long as the composite elastic modulus meets the above requirements; for example, acrylic UV-curable resin or epoxy UV-curable resin can be used. Alternatively, the adhesive resin can also be a thermosetting resin.

[0051] The composite elastic modulus of the adhesive resin after curing at 23°C is 0.5 GPa or more and 6.0 GPa or less. Furthermore, from the viewpoint of minimizing damage to the adhesive resin, the aforementioned composite elastic modulus is preferably 1 GPa or more, more preferably 2 GPa or more. Additionally, from the viewpoint of further suppressing transport losses at low temperatures, the aforementioned composite elastic modulus is preferably 4.5 GPa or less, more preferably 3.0 GPa or less. The composite elastic modulus of the adhesive resin can be adjusted, for example, by the type of adhesive resin, the molecular weight of the oligomer, the number of functional groups contained in the monomer, and their proportions. It should be noted that the composite elastic modulus in this specification is the composite elastic modulus in the thickness direction, measured based on the test method of ISO 14577.

[0052] like Figure 3 As shown, a portion of the adhesive portion 2 protrudes upward beyond the tangent line T of the single-sided surfaces (tangent points Q1 and Q2) of the adjacent optical fiber cores 10A and 10B. This protrusion can be achieved, for example, by adjusting the amount of adhesive resin applied. Here, "single-sided" refers to either above or below the line connecting the centers of the adjacent optical fiber cores.

[0053] Furthermore, the maximum value H of the height of the adhesive portion 2 protruding from the tangent T is preferably 10 μm to 100 μm, more preferably 20 μm to 50 μm. This maximum value H of the protrusion height can be set, for example, by adjusting the amount of adhesive resin applied.

[0054] Furthermore, the protrusion height is preferably greatest near the center of the adhesive portion 2 in the width direction W. That is, the protrusion height is preferably greatest near the straight line P3 passing through the tangent point of optical fiber core 10A and optical fiber core 10B. In addition, the adhesive portion 2 preferably slopes gently in a curved shape in the width direction W from near the center of the adhesive portion 2 toward the width direction ends 2a and 2b.

[0055] Furthermore, in the width direction W, each of the width-direction ends 2a and 2b of the adhesive portion 2 is located further outward than the center of each of the adjacent optical fiber cores 10A and 10B. Specifically, the width-direction end 2a is located further outward than the straight line P1 connecting the center point O1 and the tangent point Q1 of the optical fiber core 10A. Similarly, the width-direction end 2b is located further outward than the straight line P2 connecting the center point O2 and the tangent point Q2 of the optical fiber core 10B. It should be noted that the aforementioned "outer outward" refers to the outer side with the straight line P3 as the center. When the adhesive portion 2 is formed by bonding three or more optical fiber cores 10, the width-direction ends 2a and 2b are formed between the two outermost optical fiber cores 10 and one of their inner optical fiber cores 10, respectively.

[0056] For example, from the viewpoint of minimizing damage to the adhesive resin, the distance U between the width-direction end 2a and the center of the optical fiber core 10A (the distance between line P4 and line P1, which passes through the width-direction end 2a and is parallel to line P1) in the width direction W is preferably 1 / 10R (where R is the radius of the optical fiber cores 10A and 10B) or more, more preferably 1 / 5R or more. Furthermore, from the viewpoint of suppressing the degradation of transmission loss at low temperatures, the distance U is preferably 2 / 3R or less, more preferably 1 / 2R or less. The distance U can be controlled, for example, by adjusting the viscosity or coating amount of the adhesive resin. It should be noted that the same applies to the distance between the width-direction end 2b and the center of the optical fiber core 10B (the distance between line P2, which passes through the width-direction end 2b and is parallel to line P2).

[0057] Furthermore, the tear force of the adhesive portion 2 in the width direction W is preferably 0.005N to 0.200N, more preferably 0.02N to 0.10N. It should be noted that the tear force in this specification is determined based on the tear test specified in JIS C 6838:2019 (IEC 60794-1-23:2019 Ribbon tear test).

[0058] Figure 4 This is a schematic side view of the adhesive portion 2 in the fiber optic ribbon core 1 according to this embodiment. Preferably, in the longitudinal direction L, at least one of the longitudinal direction ends 2c and 2d of the adhesive portion 2 protrudes at a greater height than the central portion of the adhesive portion 2. Furthermore, as... Figure 4As in the example, more preferably, the protrusion height of the longitudinal ends 2c and 2d of the adhesive portion 2 in the longitudinal direction L is greater than that of the central portion of the adhesive portion 2 in the longitudinal direction L. The protrusion height of the longitudinal ends 2c and 2d of the adhesive portion 2 can be set, for example, by adjusting the amount of adhesive resin applied. As for the protrusion height from the central portion of the adhesive portion 2, it is preferably 20 μm or more and 100 μm or less.

[0059] [Example]

[0060] The following describes embodiments related to this disclosure, and further details this disclosure. It should be noted that this disclosure is not limited to the following embodiments.

[0061] The structure and physical properties of the manufacturing examples shown below were determined by the following methods.

[0062] (Composite elastic modulus)

[0063] The composite elastic modulus in the thickness direction of the cured adhesive resin was determined using a nanoindenter (BRUKER HYSITRON TI950 Tribolndenter) and a test method based on ISO 14577. The indentation depth was set to 100 nm, and the measurement was performed using a Berkovich indenter.

[0064] (The presence or absence of protrusions, their height, and the position of their ends)

[0065] The presence or absence of a protrusion from the tangent T in the width direction W of the adhesive portion 2, the maximum height H of the protrusion, and the positions of the width-direction ends 2a and 2c were determined using a laser microscope. The same method was used to determine whether the longitudinal ends 2c and 2d of the adhesive portion 2 in the longitudinal direction L protruded.

[0066] (Resistance to loosening)

[0067] The fiber ribbon core 1 was evaluated based on the torsion test specified in IEC 60794-1-2. The evaluation criteria are shown below.

[0068] A: It won't loosen even after being twisted 20 times at 180°.

[0069] B: Loose after 15 to 20 rotations of 180°.

[0070] C: Loose after 10 to 15 rotations of 180°.

[0071] D: Loose after being twisted 5 to 10 times at 180°.

[0072] E: Loose after being twisted less than 5 times at 180°.

[0073] (low temperature characteristics)

[0074] A thermal cycling test was conducted on the fiber ribbon core 1, repeating one cycle six times from room temperature (23℃) to -40℃ to -60℃. At 23℃ and -60℃, the attenuation per unit distance of the fiber 11 contained within the fiber ribbon core 1 was measured, and the difference between the measurements at the two temperature environments was used for evaluation. The evaluation criteria are shown below.

[0075] A: The difference in measured values ​​is less than 0.05 dB / km.

[0076] B: The difference in measured values ​​exceeds 0.05 dB / km but is less than 0.1 dB / km.

[0077] C: The difference in measured values ​​exceeds 0.1 dB / km but is less than 0.3 dB / km

[0078] D: The difference in measured values ​​is greater than 0.3 dB / km.

[0079] (Tearing force)

[0080] Tear strength was determined based on the tear test specified in JIS C 6838 (2019). In this tear test, the sample length was set to 150 mm (with an adhesive portion in the center), the chuck distance was set to 70 mm, and the tensile speed was set to 200 mm / min. Furthermore, the peak value was used as the measured value, and the measured values ​​of 5 samples for each manufacturing example were calculated, and their arithmetic mean was taken as the tear strength.

[0081] (Manufacturing Examples 1 to 42)

[0082] Using six adhesive resins with different composite elastic moduli, the presence or absence of a protrusion at the tangent T or at the longitudinal end of the adhesive portion 2 was varied, and optical fiber ribbon cores 1 were manufactured in Manufacturing Examples 1 to 42. In Manufacturing Examples 1 to 42, the tear strength was approximately 0.03 N. Furthermore, the maximum height H of the protrusion was approximately 30 μm. Additionally, the distance U in the width direction W was in the range of 0 to 1 / 2R.

[0083] For the fiber ribbon cores 1 of Manufacturing Examples 1 to 42, anti-loosening and low-temperature characteristics were evaluated. The results are shown in Table 1. In Table 1, Manufacturing Examples 8, 9, 14, 15, 20, 21, 26, 27, 32, 33, 38 and 39 are exemplary examples, and the other manufacturing examples are comparative examples.

[0084] [Table 1]

[0085]

[0086] (Manufacturing Examples 43 to 52)

[0087] Six adhesive resins with different composite elastic moduli were used to create different tear forces in the adhesive portion 2, and fiber ribbon cores 1 were manufactured in Manufacturing Examples 43 to 52. In Manufacturing Examples 43 to 52, the adhesive portion 2 had a protrusion from the tangent T, and the distance U of the adhesive portion 2 in the width direction W was between 0 and 1 / 2R. Furthermore, the maximum height H of the protrusion was approximately 30 μm. Additionally, the longitudinal ends 2c and 2d of the adhesive portion 2 in the longitudinal direction L protruded more than the central portion of the adhesive portion 2 in the longitudinal direction L. The anti-loosening properties of the fiber ribbon cores 1 in Manufacturing Examples 43 to 52 were evaluated. The results are shown in Table 2. It should be noted that Manufacturing Examples 43 to 52 are all examples.

[0088] [Table 2]

[0089]

[0090] (Manufacturing Examples 53 to 67)

[0091] Six adhesive resins with different composite elastic moduli were used to manufacture fiber ribbon cores 1 in Examples 53 to 67, resulting in different maximum values ​​H of the protrusion height in the adhesive portion 2. In Examples 53 to 67, the protrusion from the tangent T in the adhesive portion 2 was "present," and the distance U of the adhesive portion 2 in the width direction W was between 0 and 1 / 2R. Furthermore, the tear strength was approximately 0.03 N. Additionally, the longitudinal ends 2c and 2d of the adhesive portion 2 in the longitudinal direction L protruded more than the central portion of the adhesive portion 2 in the longitudinal direction L. The anti-loosening and low-temperature characteristics of the fiber ribbon cores 1 in Examples 53 to 67 were evaluated. The results are shown in Table 3. It should be noted that Examples 53 to 67 are examples.

[0092] [Table 3]

[0093]

[0094] (Manufacturing Examples 68 to 87)

[0095] Six adhesive resins with different composite elastic moduli were used to fabricate fiber ribbon cores 1 in Manufacturing Examples 68 to 87, with varying distances U in the width direction W. In Manufacturing Examples 68 to 87, the adhesive portion 2 protrudes from the tangent T. The tear strength is approximately 0.03 N. The maximum height H of the protrusion is approximately 30 μm. Furthermore, the longitudinal ends 2c and 2d of the adhesive portion 2 in the longitudinal direction L protrude more than the center portion of the adhesive portion 2 in the longitudinal direction L. The anti-loosening and low-temperature characteristics of the fiber ribbon cores 1 in Manufacturing Examples 68 to 87 were evaluated. The results are shown in Table 4. In Table 4, a distance U less than OR means that the width end 2a of the adhesive portion 2 in the width direction W is located inside line P1, and the width end 2b is located inside line P2. It should be noted that Manufacturing Examples 68 to 87 are examples.

[0096] [Table 4]

[0097]

[0098] The present invention has been described in detail above with reference to specific embodiments. However, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. Furthermore, the number, position, shape, etc., of the constituent components described above are not limited to the above embodiments and can be changed to a number, position, shape, etc., suitable for implementing the present invention.

[0099] Explanation of symbols

[0100] 1: Fiber optic cable with core wire

[0101] 2: Adhesive part

[0102] 2a, 2b: End points in the width direction

[0103] 2c, 2d: Ends in the longitudinal direction

[0104] 3: Non-adhesive parts

[0105] 10, 10A, 10B: Fiber optic core wires

[0106] 11: Fiber optic

[0107] 12: Primary resin layer

[0108] 13: Secondary resin layer

[0109] 14: Colored resin layer

[0110] T: Tangent

[0111] H: Maximum height of the protrusion

[0112] L: Vertical direction

[0113] W: Width direction

[0114] U: Distance

[0115] O1, O2: Center point

[0116] P1, P2, P3, P4: Straight lines

[0117] Q1, Q2: Tangent Point

[0118] R: radius

Claims

1. An optical fiber ribbon core, which is an intermittently connected type, wherein, among a portion or all of the multiple optical fiber ribbon cores arranged side-by-side along a width direction orthogonal to the longitudinal direction, adhesive portions formed by bonding between adjacent optical fiber ribbon cores and non-adhesive portions not bonded by the adhesive resin between adjacent optical fiber ribbon cores are intermittently provided in the longitudinal direction. The adhesive portion is disposed on one side of the optical fiber ribbon core. A portion of the adhesive portion protrudes beyond the tangent to the surface of the single-sided side of the adjacent optical fiber core. In the longitudinal direction, the height of at least one of the longitudinal ends of the adhesive portion is greater than that of the central portion of the adhesive portion. The adhesive resin has a composite elastic modulus of 0.5 GPa to 6.0 GPa at 23°C. The composite elastic modulus is the composite elastic modulus in the thickness direction determined by a test method based on ISO 14577.

2. The optical fiber ribbon core according to claim 1, wherein, The tear force when tearing the adhesive portion, as determined by the tear test specified in JIS C 6838:2019, is 0.005 N to 0.200 N.

3. The optical fiber ribbon core according to claim 1 or claim 2, wherein, The maximum height of the protrusion of the adhesive portion from the tangent is between 10 μm and 100 μm.

4. The optical fiber ribbon core according to claim 1 or claim 2, wherein, In the width direction, each of the width-direction ends of the adhesive portion is located further outward than the center of the respective adjacent optical fiber core.

5. The optical fiber ribbon core according to claim 3, wherein, In the width direction, each of the width-direction ends of the adhesive portion is located further outward than the center of the respective adjacent optical fiber core.

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