JPH0332591B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION This invention relates to certain liquid adhesive and sealant compositions that have excellent structural strength properties at high temperatures when cured and excellent resistance to thermal decay. Adhesive and sealant compositions based on cyanoacrylate monomers are known in the prior art. Representative patents for cyanoacrylates are US Pat. No. 2,784,215, US Pat. No. 2,794,788 and British Patent No. 1,196,069. Cyanoacrylate adhesive compositions are extremely sensitive and therefore their formulation must be very careful. Curing (polymerization) is generally believed to be initiated by an anionic mechanism, with water being a strong enough base to initiate curing in most cases. These adhesives are self-stable products as long as they are properly packaged, but when placed on the substrate to be bonded and thus exposed to atmospheric air and surface moisture, curing is generally relatively short. period, approximately 1
Begins within minutes and on many surfaces, almost within seconds. This extraordinary curing rate provides a number of advantages, particularly for applications using adhesive bonds in production line applications. however,
A major drawback that has traditionally limited the range of applications of cyanoacrylate adhesives has been the relatively low heat resistance of the cured adhesive; the bonded assembly is often exposed to continuous use temperatures above about normal room temperature. exposed and therefore the adhesive assembly must retain adequate strength for a considerable period of time at these high temperatures in order to retain its effective performance. In addition to strength retention by adhesives at elevated temperatures (i.e., hot strength), their adhesive layers must not be unduly affected by continuous or repeated exposure to elevated temperatures ( resistance to thermal decay). Even when difunctional acrylate monomers were used in the prior art, it was not possible to create acrylate adhesive compositions that produced significant crosslinking upon curing. Furthermore, due to the extreme reactivity of cyanoacrylate monomers, there have been considerable limitations on the addition of other components such as crosslinkers or copolymers to improve the heat resistance mentioned above. In U.S. Pat. No. 3,832,334, the issue of heat resistance is
The solution is the addition of maleic anhydride and their substitution products. Additionally, it was known in the prior art to include crosslinking agents such as allyl-2-cyanoacrylate or polymerizable acrylate esters, thus improving heat resistance. However, none of the prior art provides improved heat resistance at about 121°C (250°C) as demonstrated by the present invention. The need for such useful adhesives is therefore obvious and will prove useful in many applications. Adhesive and sealant compositions are provided which are normally liquid in the uncured state and, upon curing, have significantly improved hot strength at elevated temperatures and improved resistance to thermal decay. The composition comprises a composition of (a) at least one cyanoacrylate and (b) at least one difunctional or monofunctional polymerizable acrylate ester.
and (c) 0.1 to 10% by weight of the composition of an additive selected from the group consisting of the following compounds:
weight% and

【formula】

【formula】 【formula】

Here, R ⁷ and R ⁸ are alkyl, cycloalkyl,
selected from aralkyl, alkaryl, (d)
An anionic polymerization inhibitor and (e) an optional free radical polymerization inhibitor. The present invention overcomes the problems of prior art adhesives, in particular their failure to maintain structural integrity (hot strength) at high temperatures and their low resistance to thermal decay due to heat aging. The compositions disclosed herein are useful on a variety of surfaces, particularly steel, aluminum, phenolics, epoxies, and thermoplastic materials. The shelf life stability of curing rate is also excellent. Cyanoacrylate monomers useful in the present invention are represented by the general formula: Here, R is C _1-16 alkyl, cycloalkyl,
Alkenyl, cycloalkenyl, phenyl, or a heterocyclic group. A preferred monomer meeting this general formula is ethyl cyanoacrylate, but mixtures of the above may be used. The polymerizable acrylate ester monomers useful in the present invention may be mono- or polyfunctional, or a mixture of both, and conform to the general formula or formulas below. That is, where R ¹ is H, CH ₃ or lower alkyl, R ² is H, alkyl, alkoxy, cycloalkyl, alkenyl, arykyl, aryl, alkaryl, allyloxy group, Here, R ³ is H, C _1-4 alkyl or hydroxyalkyl, or R ⁵ OCH ₂ -, R ⁶ is H, halogen or C _1-4 alkyl, and R ⁴
is H, OH or R ⁵ O-, and R ⁵ is CH ₂ =
CR ⁶ C=0, m is an integer, preferably from 1 to 8, k is an integer, preferably from 1 to 20, and p is 0 or 1. At least one acrylate ester monomer should be present in the present compositions, generally in an amount of about 0.1 to about 10% by weight of the total composition. A preferred amount is about 1 to about 5% by weight, most preferably about 1% by weight. Among the useful monofunctional polymerizable acrylate ester monomers (formula) are hydroxyethyl methacrylate, hydroxypropyl methacrylate, isobornyl methacrylate, methyl methacrylate, tetrahydrofurfuryl methacrylate, and butyl methacrylate; Oxypropyl and methyl methacrylate and allyl methacrylate are said to be preferred. Polymerizable polyacrylate esters used according to the invention and falling under the general formula above are exemplified by, but not limited to, the materials listed below. namely, diethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, dibropylene glycol dimethacrylate, di-(pentamethylene glycol) dimethacrylate, tetramethylene dimethacrylate, ethylene dimethacrylate, neopentyl glycol diacrylate and trimethiolpropane triacrylate. , among these,
Preferred monomers are triethylene glycol dimethacrylate and polyethylene glycol dimethacrylate. Another component essential to the invention is an additive selected from the group consisting of any of the following structures: That is,

【formula】

【formula】

【formula】

The nature of R ⁷ and R ⁸ is non-critical for the purposes of the present invention and therefore any group that does not contain any group that would have an adverse effect on the compositions suitable for the purposes disclosed herein. It may be an organic group. Most commonly ^R7 and ^R8 are alkyl, cycloalkyl,
selected from the group consisting of aralkyl, alkaryl, aryl, allyloxy, alkoxy, any of which may be exceptionally large, for example containing about 200 carbon atoms or more;
Preferably it contains 6 to about 100 carbon atoms, most preferably 6 to about 50 carbon atoms. It has been found that thermal oxidative decay resistance is improved if R ⁷ or R ⁸ are made aromatic; however, this is not required to be realized for the general improvement of the present invention. . of course,
It will be appreciated that both R ⁷ and R ⁸ can consist of relatively complex ingredients, provided that neither R 7 nor R 8 contain functionality that would interfere with the additive's efficacy for its intended purpose. Useful concentration ranges for this additive include about 0.1% to about 20% by weight of the total composition;
Preferably it is about 1 to about 5% by weight and more preferably about 2% by weight. Without wishing to be bound by any theory, it is believed that the improved hot strength properties obtained from the present compositions are due to the unique combination of polymerizable acrylate esters and the maleimides described above, both of which is believed to be an important component of cyanoacrylate adhesive compositions. Theoretically speaking, maleimide additives react with cyanoacrylate monomers during polymerization. The maleimide ring is
It is cooperatively released during the reaction and grafted onto the cyanoacrylate during its polymerization. Without wishing to be bound by any particular chemical theory, it is believed that as the cyanoacrylate cures, the maleimide is incorporated into the cyanoacrylate chain. The subsequent high temperature is believed to induce a second stage of polymerization between the grafted maleimides, allowing them to form unsaturated moieties,
Therefore, it contains acrylic acid ester monomers. Crosslinks are thus formed. This unique interaction is responsible for its superior ability to withstand the common effects of heat aging and maintain structural properties such as tensile strength at temperatures of about 120°C (250F) or higher for extended periods of time. should be returned. Generally, the amount of maleimide additive that should be used is
from about 0.1 to about 20% by weight of the composition,
However, the preferred amount is about 1 to about 5% by weight, and the most preferred amount is about 2%. Amounts of about 2% or less are readily soluble in the cyanoacrylate and acrylic ester polymers at room temperature. Above this amount, the additive will remain suspended in the liquid composition and still perform its function and develop the desired properties. Among the preferred maleimide additives are the following structures. That is, Here R ⁸ is a phenyl group. This compound is
Trademarked by HVA and manufactured by E.I. DuPont de Tamour Company. It is important to maintain adequate stability of the composition without losing its rapid curing advantages. This stability can be adjusted through the use of known inhibitors of anionic polymerization. Standard acid gases such as sulfur dioxide, sulfur trioxide and nitrogen oxide are added as conventional inhibitors of anionic polymerization. However, it is preferred that a combination of sulfur dioxide and acids selected from sulfonic acids, phosphoric acids, phosphonic acids, and carboxylic acids are used in the PKa range of about -12 to 7. The most preferred combination of ingredients is methanesulfonic acid and sulfur dioxide, both of which make up about
It is present in the range of 0.005 to 10% by weight, but most preferably in the range of about 0.005 to about 0.1% by weight. The preferred ratio of _SO2 to methanesulfonic acid is 20:50. Hydroquinone, benzoquinone, naphthoquinone,
It is optional, but recommended, that an inhibitor of free radical polymerization selected from the group consisting of phenanthraquinone, anthraquinone and substituted compounds of any of the foregoing be added to the adhesive as well.
Hydroquinone is most preferred. Generally, the amount of this type of inhibitor will be approximately
0.17 to about 10% by weight, preferably 0.17 to 5% by weight, and most preferably 0.95% by weight. Other chemical agents, such as thickeners, plasticizers, diluents, etc., are likewise known to those skilled in the art, and only if these agents do not interfere with the action of the additives, which are important for their intended purpose. It is advantageously added when the conditions are favorable for operation. The compositions have good shelf life stability, eg, the compositions typically remain liquid in the uncured state at room temperature. Of course, this can be determined by simple experimental methods. The following examples are presented to demonstrate several compositions within the scope of the invention disclosed herein. These examples are not intended to be limiting as to the scope of the invention. Below is a table of each component of the composition used in each example. All percentages are by weight based on the amount of ethyl cyanoacrylate comprising the remainder of the adhesive composition.

Table: Example 1 From Table 1, the hot strength of control compositions A and B was measured at about 121°C (250°). Grit blasted and solvent washed steel laps were used to prepare lap shear samples with these compositions and the samples were then aged and aged to approx.
Tested at 121℃ (250〓). The lap shear samples were cured for 24 hours at room temperature before heat aging. After 1 hour, the lap shear tensile strength of composition A is:
It was about 91Kg/cm ² (1300psi). After 25 hours, the strength decreased to approximately 49Kg/cm ² (700psi), and after 48 hours,
Its strength was approximately 46 kg/cm ² (650 psi). Composition B was similarly tested and the results are shown in the table below. That is,

[Table] As seen from the above data, approximately 121℃
In the strength properties measured by lap tensile shear at (250〓) there is a large decrease starting in the first hours of aging and decreasing continuously until there is almost no structural integrity in the adhesive layer. These compositions are representative of the prior art and clearly demonstrate a collapse in tensile strength upon temperature release. This example is presented for comparison with the compositions of the present invention. (See Examples 2 and 3) Example 2 Compositions C and D from Table 1 are used to prepare Zagrit-blasted steel lap shear samples and the samples are heated at approximately 121°C (250°). Aged and tested. The results are displayed in the table below. That is,

【table】

TABLE The table shown above shows that the formulations of the present invention have excellent retention of hot tensile properties. This improvement is evident from a comparison of the hot strength of the prior art adhesive and the hot strength of the adhesive of the invention. Example 3 Lap shear samples were prepared as in the previous example using compositions E and F and C.

TABLE As shown, Composition E is similar to Control Composition A except that it has allyl methacrylate as an added ingredient. Composition F is also similar to Control Composition A except that it contains the added ingredient HVA. Composition C is an example of the invention. The results in the table above demonstrate that the use of HVA or acrylic ester additives alone produces very similar hot strength results in adhesive compositions. The compositions of the invention have proven to have excellent strength, especially after 6 days at elevated temperatures. Fourth Example This example demonstrates the excellent heat resistance properties of the composition of the present invention. Steel lap shear specimens were prepared as in the previous example with compositions A, F, and G, and for up to 5 days approximately 121
Heat aged at ℃ (250〓). The lap shear samples were then cooled to room temperature and stretched.
The results are shown below. That is,

TABLE As revealed by the table above, the composition G of the present invention outperforms the prior art compositions in its heat resistance ability. Composition A was a representative prior art cyanoacrylate adhesive composition, and Composition F had HVA in its formulation (see Table). This example clearly shows that the compositions of the present invention provide superior heat resistance properties over prior art compositions. Example 5 This final example shows the results from a thermal stability test (thermogram). This test consists of heating a sample of the cured composition and measuring its weight loss. This weight loss is proportional to the disintegration of the polymer. This analysis was performed using a PerkinElmer TGS using the following conditions. Temperature range 40°C to 400°C Heating rate 20°C/min Sample size Approximately 9 mg Barge gas Air flow at 40 c.c./min Speed 10 mm/min The results in the following table show that the composition of the present invention G is 280
It has been shown to retain almost 50% of its weight at 300°C and 40% of its weight at 300°C. It is clear from the table below and from Figures 1 and 2 that the composition of the invention undergoes a two-stage decomposition, the first stage starting at 160°C and representing 48% of the total sample, and the second stage at 280°C. and represents 42% of the sample weight. Contrast this with the one-step decomposition of the prior art. The prior art composition (Control A) showed total disintegration at 260°C;
Showing a weight loss of 98.8%.

【table】 [Brief explanation of the drawing]

FIG. 1 is a thermograph diagram showing the two-stage collapse of composition G described in the present invention in relation to temperature and weight loss, and FIG. 2 is a thermograph diagram similarly shown for composition A. .

Claims (1)

[Scope of Claims] 1. An adhesive composition having improved heat resistance, comprising: (a) at least one polymerizable cyanoacrylate monomer represented by the general formula; (Herein, R is C _1-16 alkyl, cycloalkyl, alkenyl, cycloalkenyl, phenyl, or a heterocyclic group.) (b) At least one polymerizable acrylate ester monomer represented by the general formula or 0.1 to 20% by weight of the total composition, (Here, R ¹ is H, CH ₃ or lower alkyl, and R ² is H, alkyl, alkoxy,
It is a cycloalkyl, alkenyl, aralkyl, aryl, alkaryl, or allyloxy group. ) or Here, R ³ is H, C _1-4 alkyl or hydroxyalkyl, or R ⁵ OCH ₂ -,
R ⁶ is H, halogen or C _1-4 alkyl, R ⁴ is H, OH or R ⁵ O-, and R ⁵ is
CH ² = CR ⁶ C = 0, m is an integer, preferably 1 to 8, and k is an integer, preferably 1 to 20.
and p is 0 or 1. ) (c) 0.1 to 20% by weight of the total composition of additives selected from the group consisting of: (where R ⁷ and R ⁸ are alkyl, cycloalkyl, aralkyl, alkaryl, aryl,
selected from the group consisting of aryloxy and alkoxy. ) (d) an anionic polymerization inhibitor present in an amount of from 0.1 to 10% by weight of the total composition; and (e) optionally from 0.1 to 10% by weight of the total composition.
An adhesive composition comprising a free radical polymerization inhibitor present in an amount of . 2. The adhesive composition according to claim 1, wherein the polymerizable cyanoacrylate monomer is ethyl cyanoacrylate. 3. Adhesive composition according to claim 1, characterized in that the polymerizable acrylate ester monomer is allyl methacrylate present in an amount of 1 to 5% by weight of the total composition. 4. The adhesive composition according to claim 1, wherein the additive (c) is represented by the following formula. (wherein R ⁸ is a phenyl group) 5. Adhesive according to claim 4, characterized in that the additive (c) is present in an amount of 2% by weight of the total composition. Composition. 6. Adhesive composition according to claim 1, characterized in that the anionic polymerization inhibitor is a combination of acid and sulfur dioxide in a ratio of 50:20. 7. Adhesive composition according to claim 6, characterized in that the acid is a sulfonic acid present in a concentration between 0.005 and 0.002% by weight of the composition. 8. The adhesive composition according to claim 7, wherein the sulfonic acid is methanesulfonic acid. 9. The adhesive composition according to claim 8, wherein the sulfonic acid is hydroxypropanesulfonic acid. 10 The optimal free radical polymerization inhibitor is hydroquinone,
Adhesive composition according to claim 1, characterized in that it is selected from the group consisting of benzoquinone, naphthoquinone, phenanthraquinone, anthraquinone and substituted compounds of any of the above. The polymerizable acrylate ester monomer corresponding to formula 11 is hydroxyethyl methacrylate,
The adhesive composition according to claim 1, characterized in that it is hydroxypropyl methacrylate, isobornyl methacrylate, methyl methacrylate, tetrahydrofurfuryl methacrylate or butyl methacrylate. 12. The adhesive according to claim 1, wherein the polymerizable acrylate ester monomer corresponding to formula 12 is tetraethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene, or glycol dimethacrylate. Composition. 13. Adhesive according to claim 1, characterized in that the composition optionally contains a sulfimide or a tertiary amine present in an amount of 0.1 to 10% by weight of the composition as a promoter of free radical polymerization. Composition.