JP3222957B2 - Metal / rubber composite vibration insulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal / rubber composite vibration isolator in which a metal fitting is adhered to a vibration isolating rubber body exhibiting a vibration isolating effect, and relates to a vibration isolator for an automobile such as a mount for an engine or a bush for a suspension link. Used as a body or as an anti-vibration support for other machinery.

[0002]

2. Description of the Related Art As a metal / rubber composite vibration isolator, a galvanized film is formed on the surface of a metal fitting made of a steel plate, and a chromate film is formed on the film by a chromate treatment.
It is known that a rubber vibration insulator is vulcanized and bonded to the surface of the chromate film via a vulcanizing adhesive after washing with hot water (see JP-A-3-182339).

[0003]

However, in the case of a metal / rubber composite vibration insulator using the above-mentioned chromate-treated metal fittings, the chromating treatment can prevent the metal fittings from rusting, but the chromium ion causes pollution. There is a problem of occurrence. Further, the chromate film tends to cause fine cracks due to heat (100 ° C. or more) at the time of vulcanizing and bonding the rubber, and there is also a problem that salt water or the like invades from the cracks and causes corrosion.

Further, in order to enhance the bonding stability between the metal fitting and the vibration-proof rubber body, a cationic electrodeposition coating is performed after the above-mentioned chromate treatment. However, the chromate treatment itself involves alkali degreasing of the metal fittings → water washing → It requires a number of steps of pickling, washing with water, removing smut, washing with water, chromate treatment, washing with water, washing with hot water, and drying.In addition, the above electrodeposition coating is required, so the number of steps is very large, It is disadvantageous in terms of productivity.

[0005] That is, an object of the present invention is to prevent rust of metal fittings without causing pollution problems and manufacturing difficulties, and to improve the adhesion stability between the metal fittings and the rubber vibration insulator. is there.

[0006]

SUMMARY OF THE INVENTION The present invention provides
As a result of intensive research on such problems, it has been found that the above-mentioned problems can be solved by treating the surface of the metal fitting with a silane coupling agent and a corrosion inhibitor,
It has been completed.

That is, a first means for solving the above-mentioned problem is a metal / rubber composite vibration isolator in which a metal member is adhered to a vibration-proof rubber member exhibiting a vibration-proof action, and the surface of the metal member is made of silane. A surface treatment film formed by a coupling agent and a corrosion inhibitor is formed, and the vibration-proof rubber body is bonded to the surface of the surface treatment film via a simultaneous vulcanization type adhesive layer. Things.

In this means, the surface treatment film of the metal fitting is
It has an organic silane compound by a silane coupling agent, and the organic silane compound film not only provides the corrosion resistance of the metal fitting, but also the adhesion stability of the adhesive layer to the metal fitting surface. That is, the organic silane compound has a hydrolyzable substituent such as an alkoxy group or a halogen, and a group that easily reacts with an organic substance such as a vinyl group, an epoxy group, or an amino group. While bonding protects the fitting from corrosion, the latter is bonded to the adhesive layer by a group that easily reacts with the organic substance, thereby improving the adhesion of the adhesive layer to the surface of the fitting.

However, the silane coupling agent does not always bond to metal atoms on the entire surface of the metal fitting.
On the other hand, the corrosion inhibitor (inhibitor) adsorbs or binds to a portion of the surface of the metal fitting where the organosilane compound is not formed, thereby completing the surface treatment film. Thereby, the corrosion resistance of the surface of the metal fitting is enhanced.
In this case, the corrosion inhibitor electrochemically suppresses the corrosion reaction, that is, reduces the electrolytic starting force between the anode and the cathode and suppresses the corrosion of the metal fitting.

As the above-mentioned metal fittings, those made of a non-ferrous metal, for example, made of aluminum, an aluminum alloy, or a magnesium alloy are preferably used. An oxide film bonded to the non-ferrous metal and an organic silane compound (silane coupling agent) are used. A silane coupling reaction is performed between the two to form an organic silane compound film.

As the vibration-proof rubber member, natural rubber (N
R) and synthetic rubber (for example, styrene butadiene rubber (S
(BR) or butadiene rubber (BR), etc., or by blending natural rubber and styrene butadiene rubber (NR / SBR) or blending natural rubber and butadiene rubber (NR / BR). It can also be molded.

As the silane coupling agent, X-
Various silane coupling agents represented by the general formula of R-Si- (OR ') ₃ can be used. in this case,
X is a methacryloxy-based, amine-based, epoxy-based, or mercapto-based active group, and R and R 'are alkyl groups. For example, γ-methacryloxypropyltrimethoxysilane,
γ-aminopropyltriethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, γ
-Use of glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane or the like is preferred.

As the corrosion inhibitor, any of an inorganic inhibitor and an organic inhibitor can be employed. For example, inorganic inhibitors include K ₂ CrO
₄ and NiCrO ₄ are preferable, and hexamethylenetetramine, oleic acid amide, stearic acid and the like can be used as the organic inhibitor.

As the simultaneous vulcanizing adhesive, a two-part curable adhesive such as a phenolic resin-based adhesive or a chlorinated rubber-based adhesive, or a one-part curable adhesive can be used.

The above-mentioned metal / rubber composite vibration isolator can be produced, for example, by undercoating a metal fitting (alkaline degreasing → water washing → water washing → drying).
After that, an organic silane treatment with a silane coupling agent is carried out, followed by an inhibitor treatment with a corrosion inhibitor, and then a simultaneous vulcanizing adhesive is applied to the surface of the surface treatment film, dried, and then protected. It can be carried out by a method in which an unvulcanized rubber for a vibration rubber body is provided on the adhesive layer and vulcanized.

In the above-mentioned organic silane treatment, immersion of a metal fitting in a silane coupling agent solution, brush coating or spray coating of the same solution on the metal fitting can be employed. Further, the inhibitor treatment can also be performed by immersing the organosilane treatment product in a solution of a corrosion inhibitor, and of course, brush coating or spray coating can also be employed. Also, by dissolving the corrosion inhibitor in the organic silane treatment liquid, and immersing the metal fittings,
The organic silane treatment and the inhibitor treatment can be performed simultaneously.

Further, a second means for solving the above problems is as follows.
A metal / rubber composite vibration isolator in which a metal member is bonded to an anti-vibration rubber member also exhibiting an anti-vibration effect, and a surface treatment film of a silane coupling agent and a corrosion inhibitor is formed on the surface of the metal member. In addition, an adhesive cured layer formed by thermosetting a thermosetting adhesive is formed on the surface of the surface treatment film that is bonded to the vibration-proof rubber body, and the adhesive cured layer of the metal fitting is formed on the adhesive cured layer. The surface-activated bonding surface of the rubber vibration insulator is bonded with an isocyanate-based adhesive.

[0018] In this means as well, for the same reason as in the first means, the surface of the metal fitting is treated with a silane coupling agent and a corrosion inhibitor to obtain the corrosion resistance of the metal fitting, and the surface of the metal fitting is protected against the surface of the metal fitting. The adhesive stability of the cured adhesive layer is obtained.

As the above-mentioned metal fittings and vibration-proof rubber members, those similar to those of the first means described above can be used. As the thermosetting adhesive, the same adhesive as the simultaneous vulcanizing adhesive in the first means can be used.

The surface activation treatment of the vibration-proof rubber body is for activating the vulcanized rubber surface with an organic acid, an inorganic acid or a physical treatment, and includes a halogenation treatment, a nitration treatment, and a cyclization treatment. , Methylene iodide treatment or plasma treatment.

In the case of the halogenation treatment, halogenated isocyanuric acid, halogenated succinimide,
Among halogenated isocyanates, N-halogensulfonamides or halogenated hydantoins, etc., a halogenation treating agent such as hydrochloric acid, hypochlorous acid, sodium hypochlorite, iodine chloride or iodine bromide as an inorganic acid. select. Among them, isocyanate iodide, dichloroisocyanuric acid, trichloroisocyanuric acid, N-dichloro-P-toluenesulfonamide and the like are preferable in terms of surface treatment performance, processing safety, treatment speed and the like. The selected halogenating agent is dissolved in a suitable organic solvent and diluted to a concentration of 0.1 to 30%, preferably 1 to 20% to obtain a halogenated solution. As the organic solvent, toluene, xylene, isooctane, dimethyl ether, ethyl acetate, methyl ethyl ketone, carbon tetrachloride, industrial thinner, or the like may be used. Then, after defatting each end surface 1a of the vibration-isolating rubber body 1 which is a vulcanized rubber, it is immersed in the halogenated solution or sprayed or coated with the halogenated solution, and is baked for a relatively short time (for example, 2, (3 seconds to 3 minutes). In this case, rinsing of the surface is often not necessary.

In the case of the above-mentioned nitration treatment, a nitrating agent is selected from among iodine nitrate, iodine azide, bromine azide, nitric acid and a mixed acid. Then, a low-concentration nitrating solution is applied to each end surface 1a of the vibration-proof rubber body 1 for a short time, and thereafter, the applied surface is sufficiently washed with water. In the case of this nitration treatment, since the reactivity is relatively large, it is necessary to perform the treatment in a sufficient safety facility.

In the case of the above cyclization treatment, a concentrated sulfuric acid solution is used as the cyclization treatment solution, and each end face 1a of the vibration-proof rubber member 1 is immersed or coated in the cyclization treatment solution at room temperature for 2 to 20 minutes. Thereafter, the attached concentrated sulfuric acid is washed off with water.

In the case of the above-mentioned methylene iodide treatment, methylene iodide is dissolved in an appropriate solvent to form a solution of 0.1 to 10%
To a methylene iodide-treated solution, and this solution is applied to the surface 1a of the rubber vibration insulator 1.

Further, in the case of the plasma treatment, 100 to 60,000 Wsec / l is applied to each end face 1a of the rubber vibration insulator 1.
Of low temperature plasma.

[0026]

Therefore, according to the first means, a surface treatment film formed by a silane coupling agent and a corrosion inhibitor is formed on the surface of the metal fitting, and the simultaneous vulcanizing adhesive is formed on the surface of the surface treatment film. Since the vibration isolating rubber body is bonded through the layer, the corrosion resistance of the metal fitting can be improved without complicating the manufacturing process and causing no pollution problem, and the bonding to the metal fitting surface can be performed. The adhesive stability of the agent layer can be obtained, and even when used in a corrosive environment, strong adhesion between the metal fitting and the vibration-proof rubber body can be maintained for a long period of time.

Also, in the second means, a surface treatment film formed by a silane coupling agent and a corrosion inhibitor is formed on the surface of the metal fitting, and the surface of the surface treatment film that adheres to the vibration-proof rubber body has heat. Because an adhesive cured layer formed by curing the curable adhesive by heat is formed, and the activated surface of the vibration-proof rubber body is bonded to the cured adhesive layer with an isocyanate-based adhesive. The same effect as the first means can be obtained.

[0028]

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1> FIG. 1 shows a metal / rubber composite vibration isolator (engine mount of an automobile) according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a columnar vibration-proof rubber body;
Are aluminum alloy fittings bonded to both ends of the vibration-proof rubber body 1. The entire surface of the metal fitting 2 is provided with a surface treatment film 3 formed of a silane coupling agent and a corrosion inhibitor, and as shown in FIG.
Is bonded to the surface of the surface treatment film 3 via a lower layer 4 and an upper layer 5 made of a simultaneous vulcanizing adhesive.

The lower layer 4 is made of a phenol resin-based primer adhesive, and the upper layer 5 is made of a chlorinated rubber-based adhesive containing chlorosulfonated polyethylene as a main component.

The production of the metal / rubber composite vibration insulator was carried out by the following steps.

-Base treatment of metal fitting 2-Base treatment of metal fitting 2 was performed in the following order. Alkaline degreasing (70-80 ° C x 5 minutes) → water washing (1 minute) → water washing (1 minute) → hot water washing (60-70 ° C x 1 minute)
→ Dry (100 ° C x 20 minutes)

-Surface Treatment- First, as an organic silane treatment, the above-mentioned undercoated metal fitting 2 was immersed in a silane coupling agent solution to form an organic silane compound film on the surface of the metal fitting 2.
The composition of the silane coupling agent solution is as follows.

Alcohol 1 liter Silane coupling agent 20 ml Water 10 ml The above immersion conditions were 30 minutes at room temperature, and the drying conditions after immersion were 100 ° C. × 20 minutes.

Next, an inhibitor treatment was carried out by immersing the metal fitting 2 having been subjected to the organosilane treatment in a corrosion inhibitor solution. The corrosion inhibitor solution was prepared by dissolving a corrosion inhibitor in a solvent so as to have a predetermined concentration. The metal fitting 2 was immersed for a predetermined time, taken out, and heated and dried at 100 ° C. for 20 minutes. As a result, a surface treatment film 3 of the organosilane compound and the corrosion inhibitor was formed on the entire surface of the metal fitting 2.

In this case, most parts of the surface of the metal fitting 2 are covered with the organosilane compound, and the remaining parts of the surface are covered with the corrosion inhibitor.
That is, it can be recognized that the silane coupling agent is coupled with Al ₂ O _{3 on} the surface of the metal fitting 2 by its hydrolyzable substituent to form Al—O—Si—RX. However, Al ₂ O ₃ is not formed on the entire surface of the metal fitting 2, and an organic silane compound film is not formed on such a portion. Then, the corrosion inhibitor adsorbs or binds to such a part, and the metal fitting 2
It is recognized that the corrosion-resistant surface treatment film 3 is completed.

-Adhesive application- The phenolic resin-based primer adhesive is applied to the surface of the surface treatment film 3 to be bonded to the vibration-isolating rubber body 1, and after this is dried, the chlorinated rubber-based adhesive is applied. And dried. The drying conditions are all 70 ° C. × 5 minutes.

-Vulcanized Adhesion- The metal fitting 2 coated with the adhesive is placed in a vulcanizing mold, the unvulcanized rubber for the vibration-proof rubber body 1 is injected, and then heated to heat the vibration-proof rubber body 1. Was vulcanized and bonded to the metal fitting 2.

(Test) The following test was conducted to confirm the effects of the above embodiment.

-Specimens-Specimens were prepared for each of Examples a to e and Comparative example a in accordance with Section 8.3.1 of JIS K6301. The composition of the rubber part corresponding to the vibration-proof rubber body 1 in each test piece is as shown in Table 1.

[0041]

[Table 1]

The material of the metal part corresponding to the metal fitting 2 in each of the test pieces is an aluminum alloy (JIS40).
A5052), and the above-described undercoating treatment was applied to each of them. ΓAPS (γ-aminopropyltriethoxysilane) or γMPS (γ-
Methacryloxypropyltrimethoxysilane)
For the inhibitor treatment, K ₂ CrO ₄ , hexamethylenetetramine (hexamine), oleic acid amide (oleamide) or stearic acid was used. That is, Examples a to
“e” is different from each other in the type of the silane coupling agent or the type of the corrosion inhibitor, and in Comparative Example a, the inhibitor treatment was not performed (see Table 2). Each of the above corrosion inhibitor solutions was prepared as follows.

In the case of K ₂ CrO ₄ , 100 to 1000 p
pm aqueous solution. In addition, each of hexamethylenetetramine, amine oleate and stearic acid was dissolved in ethanol to form 100 ppm to 1%
The solution was used.

For each of the test pieces of the above Examples and Comparative Examples, Chemlock 205 (trade name, manufactured by Road Co., USA) was used as a phenolic resin-based primer adhesive for the lower layer 4.
As the chlorinated rubber-based adhesive for the upper layer 5, Chemlock 252 (trade name, manufactured by Road Co., USA) was used.

-Contents of Test- Each of the above test pieces was subjected to a 90 degree peel test based on 8.3 of JIS K6301. The peel test was performed in combination with a salt spray test (SST) according to JISZ2371. That is, the peel test was carried out at the initial stage (without salt spray), 600 hours after salt spray, 720 hours after salt spray, and 1000 hours after the salt spray.

-Test results- The test results are shown in Table 2. In the same table, the meaning of each symbol of R-RC-CP-M in the item of the peeled state is as follows.

R: Breakage of rubber part RC: Breakage between rubber part and adhesive CP: Breakage of adhesive part M: Breakage between metal and adhesive

[0048]

[Table 2]

According to Table 2, there is no difference in the results of the initial peel test in each example. Then, as the salt water spray time becomes longer, breakage between the metal part and the adhesive in any of the examples is observed, but in the case of the comparative example, the rate of breakage between the metal part and the adhesive is determined. Greater than that of the example. From this, when the surface treatment film 3 formed by the silane coupling agent and the corrosion inhibitor is formed on the surface of the metal fitting 2 as in the present invention, the corrosion resistance or the adhesion stability of the metal fitting is higher than when only the organic silane treatment is performed. It turns out that it becomes high.

<Embodiment 2> The metal / rubber composite vibration isolator of this embodiment is a cylindrical bush, which is shown in FIGS. In the figure, reference numeral 21 denotes a cylindrical anti-vibration rubber body, 22 denotes an aluminum alloy inner metal fitting adhered to the inner peripheral surface of the anti-vibration rubber body 21, and 23 denotes an outer peripheral surface of the anti-vibration rubber body 21. This is an aluminum alloy outer cylinder fitting. The same vulcanization bonding as in the first embodiment is employed for bonding the inner cylindrical member 22 to the vibration isolating rubber body 21.

On the other hand, a surface treatment film formed by a silane coupling agent and a corrosion inhibitor is formed on the entire surface of the outer cylindrical member 23, and as shown in FIG.
A lower layer 25 and an upper layer 26 formed by thermosetting a thermosetting (simultaneously vulcanizing) adhesive on the surface of the surface to be bonded to the vibration isolating rubber body 21 are formed. Further, the vibration-proof rubber body 21
Is subjected to a predetermined surface activation treatment. Thus, the surface of the vibration-proof rubber body 21 that has been subjected to the surface activation treatment is adhered to the adhesive cured layer 26 of the outer tube fitting 23 by the isocyanate-based adhesive layer 27.

The adhesion between the vibration-proof rubber member 21 and the outer sleeve 23 was performed by the following steps. -Base treatment, organic silane treatment and inhibitor treatment of the outer tube fitting 23-The base treatment, organic silane treatment and inhibitor treatment of the outer tube fitting 23 were performed in the same manner as in Example 1.

-Formation of Adhesive Cured Layer- The above-mentioned Chemloc 205 was applied as a lower layer 25 to the surface (inner peripheral surface) of the surface treatment film 24 of the outer cylindrical metal member 23 bonded to the vibration-proof rubber body 21 and dried. Thereafter, Chemrock 220 (chlorinated rubber-based adhesive) manufactured by US Road Co., Ltd. was applied as the upper layer 26 and dried. Drying condition is 7
0 ° C. × 5 minutes. Then, these adhesives were thermally cured at 150 ° C. for 20 minutes to form the cured adhesive layers 25 and 26.

-Surface Activation Treatment- After the outer peripheral surface of the vibration isolating rubber body 21 is subjected to a degreasing treatment with a solvent, a 3% solution of trichloroisocyanuric acid (a diluent is an organic solvent) is applied to the outer peripheral surface. Was activated.

-Adhesion- After an isocyanate-based adhesive is applied to the outer peripheral surface of the vibration-proof rubber body 21, the vibration-proof rubber body 21 is press-fitted into the cylindrical hole of the outer metal fitting 23 and compressed radially inward. The isocyanate-based adhesive was cured under a heating condition of 120 ° C. for 20 minutes while the elastic restoring force of the rubber was applied. As a result, the isocyanate-based adhesive layer 27 was formed, and the vibration-proof rubber body 21 and the outer sleeve 23 were integrated.

(Test) The following test was performed to confirm the effect of the above embodiment.

-Test piece-The test piece is the above-mentioned cylindrical bush, and was prepared for each of Examples f to h and Comparative example b according to the method described above. Table 1 shows the rubber composition of the vibration-proof rubber body in each test piece. The materials of the metal fittings 22 and 23 were aluminum alloy (A5052, A6063 or A7003 in JIS H4000), the above-mentioned γAPS was used as the silane coupling agent, and oleic amide was used as the corrosion inhibitor. Did not undergo inhibitor treatment (see Table 3).

Each of the test pieces of the above Examples and Comparative Examples was provided with the above Chemlock 2 for the cured adhesive layers 25 and 26.
No. 05 and No. 220 were used, and a urethane bond was used as an isocyanate adhesive. The baking condition of the isocyanate-based adhesive was 150 ° C. for 20 minutes.

-Contents of Test- For each of the above test pieces, the outer cylindrical fitting 23 is held, and an axial load is applied to the anti-vibration rubber body 21 and the inner cylindrical fitting 22 to punch them out. The test was performed.
The punching test was also performed in combination with the salt spray test as in the test in Example 1.

-Test results- The test results are shown in Table 3. In the same table, the meaning of each symbol in the item of the peeled state is the same as in the case of Table 2.

[0061]

[Table 3]

According to Table 3, in the case of this test also, Example 1 was used.
The same tendency as in the case of the test is shown. That is, in each case, there is no difference between the initial test results. Then, as the salt water spraying time becomes longer, the breakage between the metal fitting 23 and the isocyanate-based adhesive layer 27 is observed in all the examples. Greater than that of the example. From this, the usefulness of the present invention is also supported in Example 2.

In particular, instead of directly bonding the vibration-isolating rubber body 21 to the surface of the aluminum alloy fitting 23 with an isocyanate-based adhesive, the surface-treating film 24 and the heat-cured adhesive cured layers 25 and 26 are used. Since the isocyanate-based adhesive is applied after covering the ground, the anti-vibration rubber body 21 which is a vulcanized rubber can be firmly bonded without subjecting the metal fitting to chromate treatment or cationic electrodeposition coating. Can be done.

In this case, the organosilane compound of the surface treatment film 24 is bonded to the inorganic metal fitting 23 and the phenol-based adhesive cured layer 25 to bridge the two, and furthermore, the phenol-based adhesive cured layer 25 and the chloride are cured. Rubber adhesive cured layer 2
6, between the cured layer of the chlorinated rubber-based adhesive 26 and the isocyanate-based adhesive layer 27, and between the isocyanate-based adhesive layer 27 and the activated surface of the vibration-isolating rubber body 21, respectively. The above-mentioned fitting 23
It is recognized that the vibration-proof rubber body 21 and the vibration-proof rubber body 21 are firmly bonded.

The method of manufacturing the vibration isolator described in each of the above embodiments is merely an example, and the conditions of each step are determined by the material of the bracket,
Needless to say, it can be appropriately changed according to the type of the adhesive used.

Regarding the second embodiment, the isocyanate-based adhesive may be applied to the metal fitting, or may be applied to both the metal fitting and the vibration-proof rubber body.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a vibration isolator according to a first embodiment.

FIG. 2 is a cross-sectional view of a bonding portion of the vibration isolator according to the first embodiment.

FIG. 3 is an exploded sectional view of the vibration isolator according to the second embodiment.

FIG. 4 is a cross-sectional view of a bonding portion of the vibration isolator according to the second embodiment.

[Explanation of symbols]

 1,21 Anti-vibration rubber body 2,22,23 Metal fitting 3,24 Surface treatment film 4,5 Simultaneous vulcanization type adhesive layer 25,26 Adhesive cured layer 27 Isocyanate type adhesive layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B32B 1/00-35/00 C08J 5/12 F16F 15/00-15/36

Claims (2)

(57) [Claims] 1. A metal / rubber composite vibration isolator comprising a metal member bonded to a vibration-proof rubber member exhibiting a vibration-proof action, wherein the surface of the metal member is treated with a silane coupling agent and a corrosion inhibitor. A metal / rubber composite vibration isolator, wherein a film is formed, and the vibration isolating rubber body is adhered to the surface of the surface treatment film via a simultaneous vulcanization type adhesive layer. 2. A metal / rubber composite vibration isolator having a metal member adhered to a vibration-isolating rubber member exhibiting a vibration-proofing effect, wherein a surface-treated film of a silane coupling agent and a corrosion inhibitor is provided on the surface of the metal member. Is formed, and an adhesive cured layer formed by thermosetting a thermosetting adhesive is formed on the surface of the surface treatment film that adheres to the vibration-proof rubber body. A metal / rubber composite vibration isolator, characterized in that the surface of the vibration isolating rubber body that has been subjected to the surface activation treatment is bonded to the cured layer with an isocyanate-based adhesive.