JPS59196377A - Structural adhesive - Google Patents

Abstract

PURPOSE:To provide a solventless structural adhesive having excellent bond strength and heat resistance and suitable for use in bonding metals to each other, by incorporating a specified prepolymer having epoxy groups and a hardener for epoxy resin as essential ingredients. CONSTITUTION:An acrylonitrile/butadiene copolymer (A) having carboxyl groups in the molecule, an epoxy resin (B) and a bisphenol compd. (C) such as bisphenol A or bisphenol F are subjected to an addition reaction in such a proportion that the epoxy group is used in a quantity of at least 1.1 times by equivalent the combined quantity of the carboxyl and phenolic hydroxyl groups, thus obtaining a prepolymer having epoxy groups. The desired structural adhesive is obtd. by incorporating said prepolymer and a hardener (e.g. dicyandiamide or 2-methylimidazole) for epoxy resin as essential ingredients.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a structural adhesive, specifically a liquid acrylonitrile-butadiene copolymer having carboxyl groups (
NBR), an epoxy resin, and a bisphenol compound, and the epoxy group is obtained by addition reaction at an equivalent ratio of 1.1 times or more to the total number of equivalents of carboxyl group and phenolic hydroxyl group. The present invention relates to a heat-curable structural adhesive that can be manufactured without using a solvent in all manufacturing steps, and that also has excellent bonding workability.

Traditionally, the technology for making structural film adhesives has been to dissolve solid polymers such as NBR or solubilized nylon in a solvent and mix them with epoxy resin, etc., make a uniform solution, and then form it into a tingling flat shape, e.g. by separating it. There is a method of obtaining a film adhesive by coating it on a liner with good formability and thoroughly drying the solvent.

Dissolving solid NBR in a solvent, blowing hot air to dry the solvent, and recovering the solvent to prevent pollution requires fairly large-scale equipment and a considerable amount of energy. However, in today's world where energy prices have risen, there are many problems in terms of economic efficiency.

In addition, if more than 1% of the solvent remains, it may foam during curing, making the bond incomplete, so careful attention must be paid to the remaining solvent during manufacturing. Ta.

Conventionally, solvent-free film adhesives were produced by
- A combination of a solid or nearly solid epoxy resin and a latent curing agent as described in British Patent No. 15781, a liquid epoxy resin as described in British Patent No. 1185895, polyvinyl acetal, NBR
There is a combination of a latent curing agent and a latent curing agent, but when used as a structural adhesive in the manufacture of honeycomb sandwich panels, the viscosity of the adhesive decreases too much when it is heated and hardens, causing it to drip. It could not be used to manufacture panels.

The present invention has been made in order to overcome the drawbacks of the prior art, and aims to provide a solvent-free structural adhesive having excellent adhesive strength and heat resistance, and particularly for bonding metal to metal and/or metal honeycomb adhesives. It is used as a medium-temperature curing film adhesive for bonding metal surfaces.

This object of the invention is achieved by the following adhesive.

That is, the present invention contains (1) (A) an acrylonitrile-butadiene copolymer having a carboxyl group in the molecule, CB) an epoxy resin, and (C) a bisphenol compound, in which the epoxy group is a carboxyl group. 1.1 for the total number of equivalents of phenolic hydroxyl groups
A structural adhesive characterized by containing a prepolymer having an epoxy group obtained by addition reaction at an equivalent ratio of 2 times or more, and (2) an epoxy resin curing agent, and has a softening point determined by the durans mercury method. It is essential that it be semi-solid at 30°C or higher and at room temperature.

There is an invention disclosed in Japanese Patent Application Laid-Open No. 47-42899 that is relatively similar in structure and purpose to the present invention having such a structure. In Example 5 of the publication, Hyc
It contains a component obtained by terminally modifying arCT B N with an epoxy resin and epoxidizing it, an epoxy resin, bisphenol A, and dicyandiamide (DICY), which is an epoxy curing agent, and is used for joining aluminum alloys as in the present invention. Shows strong adhesion against shearing forces and peeling.

The present invention and the invention disclosed in this publication have almost the same raw materials originally used before modification, and their uses are also the same, but the composition of the present invention contains ( C) The component does not exist in its original form,
While various epoxy resins, bisphenol A type resins, and CTBN skeleton epoxy resins have already been incorporated into molecules by arbitrarily linking them through addition reactions, in the invention of this publication, bisphenol A exists as is as eight bisphenol molecules, and in this respect they are different.

As a result, the composition of the present invention has a broader molecular weight distribution and a higher average molecular weight than the mixture of the invention of the publication that does not involve prepolymerization. By the way, (C
) component is a solid substance at room temperature, but when dissolved in epoxy, its molecules are smaller than epoxy, so it has the effect of lowering the overall viscosity. From this, the composition of the present invention has a higher viscosity and is closer to a solid than the composition of the invention disclosed in the publication, and the temperature change in the degree of viscosity is also smaller. In other words, even if the composition of the present invention and the composition of the invention of the publication have similar viscosities at room temperature,
Comparing the viscosity at a curing temperature 150°C higher, the composition of the present invention is much more viscous and can form a good fillet of honeycomb and face material without dripping, whereas the composition of the publication As can be seen from the explanation of honeycomb adhesion in Example 1, the viscosity of the product is so low that the composition applied to one side wets the uncoated surface, and with such a low viscosity, dripping is severe and it is difficult to actually apply it. It is presumed that it cannot be used.

In addition, in the invention disclosed in the publication, since the reaction of component (C) is carried out simultaneously with the curing reaction of epoxy, heat generation is large, curing time is long, and furthermore, the reaction of component (C) is caused by unreacted component (C). In some cases, the water resistance is inferior, and it cannot help but be said that the utility value is lower than that of the present invention. To summarize the comparison between the present invention described so far and the invention in this publication, both inventions have relatively common raw materials and uses, but (
C) The form of the component is different, and accordingly the molecular weight distribution and average molecular weight are different, and the properties such as dripping at the curing temperature, the time required for curing, and water resistance are different. The composition of the present invention is excellent in all of these different properties, and the invention disclosed in the publication has a fatal problem of sagging when used as a film adhesive for manufacturing honeycomb sand inch panels as in the present invention. occurs.

In the present invention, component (A) is a liquid acrylonitrile-butadiene copolymer having a plurality of carboxyl groups at the terminal end and/or in the molecular chain. There is a HycarCT BN series made by Manufacturer. These have a molecular weight of about 3500 and a carboxyl content of 2.4-3%.
The average number of carboxyl groups per molecule is 1.8 to 2.3
There are three types of acrylonitrile content of 10.18.27%.

In the present invention, the amount of component (A) used is (A) CB) (
5 to 40% by weight based on the total amount of each component of C), component CD) described below, curing agent, and organic diluent such as xylene resin.
, preferably 15 to 30% by weight. If the amount of component (A) used is less than 5% by weight, the adhesive will have poor peeling force and dynamic fatigue properties and cannot be used as a structural adhesive. Furthermore, if the amount used exceeds 40% by weight, the heat resistance will be significantly impaired, so it cannot be used as a structural adhesive.

The epoxy resin which is component CB) in the present invention is preferably a substantially bifunctional epoxy resin such as diglycidyl ether of bisphenol A. Trifunctional or higher functional epoxy resins, such as novolak epoxy, tend to cause the prepolymer to gel, so they are rarely used other than as a small part of the CB) component, but bisphenol A
Epoxy resins other than epoxy resins can be used alone or in a blend as appropriate as the CB) component as long as they are bifunctional.

The amount of component CB) to be used is determined when the epoxy group in component CB) is (
After completing the addition reaction with the carboxyl group and phenolic hydroxyl group contained in component A) and component (C), it is necessary to have as much as the remaining amount, and the epoxy group is equivalent to the carboxyl group and the phenolic hydroxyl group in an equivalent ratio. It is sufficient if it is in excess of 10% or more of the total amount.

Component (C) of the present invention is a bisphenol compound represented by bisphenol A1 bisphenol F and the like having the following structural formula.

Bisphenol A: H3 Bisphenol F: The amount of component (C) used is limited by the equivalence ratio mentioned above, but apart from that, each component of (A), (B), and (C),
The amount is 1 to 20% by weight based on the total amount of component (D), curing agent, and organic diluent such as xylene resin, which will be described later. If it is less than 1% by weight, the molecular weight distribution and average molecular weight will be modified, resulting in honeycomb adhesion. It is not possible to impart suitable flow characteristics to the 2
If it exceeds 0% by weight, the average molecular weight becomes too high and it becomes hard, resulting in poor bonding workability and poor adhesive properties, especially water resistance.

In addition, solid epoxy resin and (A) without using component (C)
) components, a film suitable for bonding work can be obtained, but the adhesive properties are insufficient and this is not preferred.1 In the present invention, the above components (A), CB), and (C ) components are prepolymerized (1
) In addition to the ingredients, an epoxy resin curing agent is added.

This epoxy resin curing agent is a general curing agent for epoxy resins, and its type, combination, loading, etc. should be appropriately selected depending on the purpose, and there are no special restrictions. Considering the heat-curable adhesive that is the object of the present invention, it is preferable to use a latent curing agent. There is no need to limit it to latent curing agents.

Examples of curing agents include guanidine curing agents represented by dicyandiamide (DICY), BF3, BF3 represented by monoethylamine, amine compounds, imidazoles represented by 2-methylimidazole, and imidazoles such as imidazole metal salts and imidazole acid compounds. Examples include, but are not limited to, various compounds such as, acid anhydrides typified by anopyromellitic acid, diamines typified by diethylenetriamine (DETA), and tertiary amines typified by benzyldimethylamine.

Preferred methods for producing component (J) in the present invention include a prepolymerization method, which is not shown below.

It is widely known that the carboxyl groups and phenolic hydroxyl groups contained in components (A) and CC) undergo an addition reaction with epoxy groups at a temperature of around 170°C or slightly lower and the action of a catalyst. The reaction between a carboxyl group and an epoxy group occurs, for example, when curing epoxy with an acid, and the reaction between a phenolic hydroxyl group and an epoxy group is also used, for example, when making solid epoxy from liquid epoxy and bisphenol A. ing. Two to three examples of methods for producing prepolymers using these reactions are as follows.

That is, the total amount of each component (A) CB) and (C) is 1
When mixed at 50°C, component (C) is dissolved to obtain a uniform brown transparent liquid. When a small amount of triphenylphosphine is added as a catalyst, the reaction heat reaches the maximum temperature in about 10 minutes, and the reaction is substantially completed in several tens of minutes, completing the prepolymerization.

In addition, as another method, the material to be prepolymerized (A)
CB) A prepolymer is obtained by keeping each component of (C) at 200°C for 10 hours. The catalyst may be charged from the beginning and heated to homogenize it. In this case, the reaction is rapidly activated when the temperature reaches 150°C.

Furthermore, prepolymerization is also possible by mixing component (A) and component CB) at 150° C., adding a catalyst to react, and then adding component (C). Also commercially available (
A material made by reacting component A) and component CB) with a catalyst and (C)
Similar prepolymerization can be obtained by adding the ingredients and heating to 150°C. Among the prepolymerization reactions, the reaction between carboxyl groups and epoxy groups is mostly completed within 10 to 20 minutes, but the reaction between phenolic hydroxyl groups and epoxy groups needs to be maintained for several tens of minutes to complete. is necessary.

The adhesive used in the present invention is obtained by uniformly dispersing a curing agent in this prepolymer, and appropriately mixing epoxy resin, fillers, coupling agents, etc. to adjust the tack and softening point.

The adhesive of the present invention can be formed into a film by, for example, the method described in Japanese Patent Publication No. 57-15781 mentioned above.

Earlier, component (1) obtained by prepolymerizing components (A), CB, and (C) and a curing agent were shown as essential components for the present invention. For the purpose of finely adjusting the temperature according to the application, an epoxy resin, which is a component CD), can be added.

Crystalline organic voice cars such as polyoxymethylene, organic fillers such as crystalline cellulose powder, inorganic fillers such as titanium oxide, calcium carbonate, finely powdered silica, tar, etc.
Optional ingredients such as dyes such as phthalocyanine blue and oil dyes, fiber reinforcing agents such as chopped glass fibers and chopped aromatic polyamide fibers, silane coupling agents, and titanium coupling agents may be blended depending on the purpose.

Hereinafter, the present invention will be specifically explained based on Examples and Comparative Examples. The blending values in Table 1 are parts by weight, and the numbers in parentheses indicate equivalent ratios.

Example 1 First, components (A), CB, and (C), which are raw materials for a prepolymer, were weighed into a 300 cc stainless steel beaker using the formulations and amounts shown in Table 1. When this is stirred while being heated in an oil bath at 150°C, the crystals of the bisphenol compound (C) component are no longer visible and it becomes a brown transparent and uniform liquid, when 0.3 weight of trinoenylphosphine is added as a catalyst. When adding %, the temperature reaches 200℃ in about 10 minutes.
When the temperature rises to nearly 100%, the reaction substantially ends and a prepolymer is obtained. When a portion of this was sampled and returned to air temperature, it became a brown transparent solid with no tack and elasticity, but when it was poured into the prepolymer at 150° C. again, it dissolved and mixed uniformly with the prepolymer.

Next, component CD), which had been melt-blended in advance, was added to the prepolymer heated in an oil bath and stirred uniformly to obtain a composition containing no curing agent. Although this composition was tacky at room temperature, it was not sticky, translucent, brown in color, and could be easily bent by hand, showing plasticity.

A curing agent was added to this curing agent-free composition and kneaded in a heated three-roll mill at 50 to 60°C to uniformly disperse the mixture to obtain the adhesive of Example 1. And this adhesive, 80
A sheet of adhesive is extruded with a coarse nonwoven fabric of 0.10 mm in thickness by sandwiching it between two rolls rotating at a constant speed while circulating warm water at a temperature of °C between two pieces of release paper. did. In addition, the gap between the rolls is set to 0.15a,
When the extrusion speed was set to 1 cyn/sec, a supported film with a thickness of about 0.25 twyn was obtained. Like before it was made into a sheet, it is tacky at room temperature and sticks to the highly active aluminum surface, which has been surface-treated for adhesion, when pressed lightly, but peels off cleanly when pulled with normal force. In addition, the films stick together when lightly pressed together, and peel off cleanly when pulled slowly, making it possible to correct adhesion failures and improve workability during bonding.

In addition, when we used this film to bond an aluminum honeycomb core and an aluminum plate, it became soft due to heat before it hardened, so the resin gathered on the tangent to the core on both the top and bottom plates, forming a fillet in good condition. Was. And no resin dripped along the nodes of the honeycomb core. From this, it was found that the adhesive of Example 1 was suitable for bonding the honeycomb core and the face plate.

0.5 mm to evaluate the adhesive strength of the adhesive of Example 1
T-peel and tensile shear adhesion test specimens were prepared using 1.6 mm thick chromic acid etched clad aluminum as adherends.

T-type peeling involves sandwiching a 0.25 to 0.31 thick sheet adhesive containing a nylon knit carrier between two adherends, and exposing the test piece to 120°C under a pressure of approximately 1.5 kg/cyf.
After pressing for 30 minutes, the pieces were cut into 1-inch pieces using shearing, and 5 pieces excluding both ends were used for testing. On the other hand, the tensile shear test was conducted after 1/2 inch overlap and curing in an air oven at 120°C for 60 minutes, followed by standing in an atmosphere of 23°C and 80°C for 10 minutes, respectively.

The tensile shear test was conducted using six test pieces for each test item. Note that T-shaped peeling was performed at a tensile speed of 50 wnn/min, and tensile shearing was performed at a tensile speed of 1 mm/min.

The results of each test are shown in Table 1.

Also, when I investigated the shelf life of this adhesive, I found that it was 4.
7 days in a 0℃ atmosphere, and an additional 6 months at -18℃
The appearance and adhesive strength did not change even when the film was sealed and stored in a refrigerator.

Examples 2-5 Adhesives were prepared in a manner similar to Example 1 and T-peel at 23°C and tensile shear at 23°C and 80°C were measured. The results are shown in Table 1. In addition, the shelf life of Example 2 is 4.
7 days for Examples 3 and 4, and 1 day for Example 5.

'L'l Kaisho 59-19 [:37'/ (6) *1: Trade name CT B N 1300x 13, liquid acrylonitrile-butadiene copolymer with an average of 1.9 functionalities and having a carboxyl group at the end, molecular weight approx. 3500, 27% acrylonitrile amount (manufactured by BF Gutdrich) *2: Trade name CT B N 1300 ff110% (manufactured by BF Gutdrich) *3
:Product name Epicote 828, epoxy equivalent approximately 190,
Liquid at room temperature, average molecular weight about 380 (manufactured by Yuka Shell Epoxy Co., Ltd.), *4: Product name Ebiko 1-834, Epoxy Toichi 230-270, semi-solid at room temperature, average molecular weight about 470 (manufactured by Yuka Shell Epoxy Co., Ltd.), *5: Product name Epicote 10
07, Epoxy equivalent: about 1750-2200° Melting point: about 13
0°C, average molecular weight approximately 380 (manufactured by Yuka Sil Eboxy Co., Ltd.)
, *6: Imidazole compound, manufactured by Shikoku Kasei Co., Ltd. *7:
Imidazole compound, manufactured by Shikoku Kasei Co., Ltd. In parentheses is (A
) and (C) component, when the total equivalent of carboxyl groups and phenolic hydroxyl groups contained in component (C) is 1.0.
Numerical values indicating the proportions contained in component (A), component (C), and the proportion of epoxy groups contained in component CB).

According to the U.S. Federal Standard MMM-'A-132 for metal-to-metal structural epoxy adhesives, Type 1,
In class 2, the tensile shear is 24 ± 3 °C and -55 ± 3 °C.
2500PS I (175,75kg/cn?) or more, 1250PS I (87,875k at 82±3℃)
g/c-of) or above, T-peel must be above 15 lb/in (6,75 ka/in) g at 24±3°C, but in Examples 1 to 5, the data at -55°C is Although it is chipped, it satisfies this required value at room temperature (23°C) and 82°C, and the T-shaped peeling is within the desired range, so it can be suitably used as a structural adhesive.

Comparative Example 1 Carboxyl group-containing NBR (CT B
N 1300x 13) 20% and epoxy resin (Epicoat 1004: Epoxy 875-975
, melting point: about 100°C, molecular weight: about 1600) was uniformly concentrated at 150°C, and as in Example 1, triphenylphosphine was added to carry out an addition reaction to obtain something similar to a prepolymer. This product was tack-free at room temperature, brown and translucent, and had an appearance similar to that of the example. However, 50% of epoxy resin (Epicoat 828) was added to this product.
When 0% by weight was added and mixed, the compatibility was poor and a stain was produced. Sheeting was possible in the same way as in Examples 1 to 5, but the adhesive strength was poor and it could not be used as a structural adhesive.

Comparative Example 2 Carboxyl group-containing NBR (CT B
N 1300x 15) 20 parts by weight of bisphenol A, 1 part by weight of bisphenol A, and 45 parts by weight of epoxy resin (Epicoat 828) were made into a prepolymer, but gelation occurred within 10 minutes after adding a catalyst, and the adhesive It was impossible to manufacture. At this time, the equivalent ratio of the epoxy groups is about 1.0.

From Comparative Examples 1 and 2, it can be seen that the blending of a bisphenol compound is essential to obtain an adhesive having excellent adhesive strength and appropriate hardness, and the amount used must also be within a specific range.

As explained above (carboxyl group-containing liquid NBR,
The adhesive of the present invention, which contains an epoxy resin and a bisphenol compound modified in a specific range, and further contains a curing agent, does not use any solvent, so it does not require a drying process.
Since it does not require a solvent recovery process, manufacturing costs can be significantly reduced, and it is also excellent in workability with adhesive saws and bonding, so it is suitably used as an adhesive for I-building.

Patent applicant: Yokohama Rubber Co., Ltd. Representative Patent Attorney Tatsuo Ito Representative Patent Attorney Tetsuya Ito

Claims (1)

[Claims] (1) Contains (A) an acrylonitrile-butadiene copolymer having a carboxyl group in the molecule, CB) an epoxy resin, and (C) a bisphenol compound, in which the epoxy group is the sum of the carboxyl group and the phenolic hydroxyl group. 1.1 for the number of equivalents of
A structural adhesive characterized by containing a prepolymer having an epoxy group obtained by addition reaction at a double or more equivalent ratio, and (2) an epoxy resin curing agent.