Abstract:
A novel neopentyl α-cyanoacrylate is provided. It has superior adhesive properties even at high temperatures and whitening-preventing property.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a novel α-cyanoacrylate and a cyanoacrylate-based adhesive composition containing same. 
     α-Cyanoacrylates such as methyl α-cyanoacrylate and ethyl α-cyanoacrylate are polymerized and cured rapidly by the action of a small amount of water present on the surface of a material to be bonded and afford an adhesive force of an extremely high strength, so are widely used as room-temperature one-pack type instantaneous adhesives for the bonding of metals, plastics, rubber, wood and the like. 
     As α-cyanoacrylate there are known propyl α-cyanoacrylate, allyl α-cyanoacrylate, propargyl α-cyanoacrylate, 2,2,2-trifluoroethyl α-cyanoacrylate, 2,2,3,3-tetrafluoropropyl α-cyanoacrylate, 2-methoxyethyl α-cyanoacrylate, 2-ethoxyethyl α-cyanoacrylate and the like in addition to the above mentioned methyl and ethyl α-cyanoacrylates. 
     Generally, in the case where an α-cyanoacrylate is used as an adhesive, a portion thereof voltilizes and is polymerized by water contained in the air and adheres as white powder to the surrounding portion of a bonded part (whitening phenomenon), thus impairing the appearance of the bonded material. When used in the assembly of electric and electronic parts, the volatilized monomer contaminates a contact portion and causes defective contact, or cures in a moving part, thereby causing malfunction. Moreover, the thermal stability of a cured product is not sufficient and the bonding strength is reduced rapidly over 100° C. It is known that α-cyanoacrylates having an unsaturated bond in the ester portion have improved thermal stability. In this case the cured or adhered portion is heat treated at an appropriate temperature (100° C.-150° C.) in order to improve the thermal stability. However, the adhesive properties at a high temperature are not improved. 
     It is the object of the present invention to overcome the above mentioned drawbacks of the prior art. More concretely, it is the object of the present invention to provide a novel compound having superior adhesive properties as an instantaneous adhesive and superior in whitening-preventing property and thermal stability including high temperature adhesive properties. 
     SUMMARY OF THE INVENTION 
     The present invention resides in a novel neopentyl α-cyanoacrylate having the chemical structural formula: ##STR1## and an adhesive containing the above compound as an essential component. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The novel compound, neopentyl α-cyanoacrylate exhibits excellent instantaneous adhesive properties. It has a melting point of 40° C. and is a solid at a room temperature It can be used itself as a hot-melt type instantaneous adhesive and also used as a liquid instantaneous adhesive in admixture of conventional one or more cyanoacrylates in the same mananer as conventional instantaneous adhesives. The instantaneous adhesive containing neopentyl α-cyanoacrylate as an essential component does not induce the whitening phenomenon and is superior in thermal stability, especially in high temperature-bonding strength. 
     Neopentyl α-cyanoacrylate may be used alone or in combination with conventional one or more α-cyanoacrylates. 
     Such conventional α-cyanoacrylates are those represented by the following general formula: ##STR2## wherein R is a hydrocarbon group such as alkyl, alkenyl, or alkynyl, or an alkoxy hyrocarbon group such as alkoxyalkyl. Examples are methyl α-cyanocrylate, ethyl α-cyanoacrylate, isopropyl α-cyanoacrylate, those wherein R is alkoxyalkyl, e.g. 2-methoxyethyl α-cyanoacrylate and 2-ethoxyethyl α-cyanoacrylate, those wherein R is alkenyl, e.g. allyl α-cyanoacrylate, and those wherein R is alkynyl, e.g. propargyl α-cyanoacrylate. 
     When using conventional cyanoacrylates in combination with neopentyl α-cyanoacrylate, the latter is preferably in an amount of 85 wt% or less, more preferably 5 to 85 wt% based on the weight of adhesive components. If the amount of neopentyl α-cyanoacrylate is more than 85 wt%, the composition becomes a solid at a room temperature (i.e. 20° C.). 
     Neopentyl α-cyanoacrylate of the present invention may be prepared by the following reactions. 
     Neopentyl α-cyanoacetate having the following structural formula: ##STR3## is prepared and then it is reacted with formaldehyde or paraformaldehyde in the presence of a basic catalyst to produce a condensation polymer, and then the condensation polymer thus produced is heat-depolymerized or thermally decomposed to produce nelpentyl α-cyanoacrylate. 
     Neopentyl α-cyanoacrylate thus obtained is a solid at a room temperature but it is desirable to add thereto a stabilizer in order to store it more stably. Examples of such stabilizer include, as anionic polymerization inhibitors, fulfurous acid (SO 2 ), sultone compounds, organic sulfonic acids, mercaptans, trifluoroacetic acid, and fluoroboric acid, and as radical polymerization inhibitors, quinones, catechol, pyrogallol, and 2,6-di-t-butylphenol. The amount of these stabilizers differs depending on the respective inhibiting abilities, but is preferably in the range of 1 to 10,000 ppm, more preferably 10 to 1,000 ppm, relative to the monomer. 
     The following examples are given to illustrate the present invention in more detail. The &#34;part&#34; and &#34;%&#34; in the following description are all by weight. 
     EXAMPLE 1 
     Preparation of Neopentyl α-Cyanoacetate 
     51 g (0.6 mole) of cyanoacetic acid, 74 g (0.84 mole) of neopentyl alcohol, 1 g of sulfuric acid and 100 g of toluene were reacted under reflux and water produced was removed by azeotropic distillation. Thereafter, the mixture thus produced was cooled to a room temperature and filtered to remove insoluble matter. The filtrate was washed with water and dried overnight with magensium sulfate. Then, the desiccant was filtered off and the solvent was removed under a reduced pressure, followed by vacuum distillation to afford 87.1 g of neopentyl α-cyanoacrylate (b.p. 79°-81° C./ 3 mmHg, yield 94%). 
     1 R (neat)cm -1  : 2262, 1751 
     60 MHz  1  H-NMR (CDCl 3  /TMS) δ(ppm): 3.87 (s, 2 H), 3.46 (s, 2 H), 0.97 (s, 9 H) 
     90 MHz  13  C-NMR (CDCl 3 ) δ(ppm): 162.91, 113.06, 75.41, 31.03, 25.86, 24.30 
     Preparation of Neopentyl α-Cyanoacrylate 
     46.5 (0.3 mole) of neopentyl α-cyanoacetate, 8.1 g (0.27 mole) of paraformaldehyde, 140 g of toluene and 46.5 mg of triethylenediamine were reacted together under reflux and water was removed by azeotropic distillation. Then, 23.5 g of dioctyl phthalate, 0.465 g of hydroquinone and 0.93 g of phosphorus pentoxide were added and depolymerization allowed to take place at 150°-210° C. under a reduced pressure to afford 21.65 g of crude neopentyl α-cyanoacrylate. Redistillation thereof afforded (8.3 g of neopentyl α-cyanoacrylate (b.p. 65°-67° C./2 mmHg, m.p. 40°-41° C., yield 36%). 
     60 MHz  1  H-NMR (CDCl 3  /TMS) δ(ppm): 7.01 (s, 1 H), 6.61 (s, 1 H), 3.95 (s, 2 H) 1.20 (s, 9 H) 
     90 MHz  13  C-NMR (CDCl 3 ) δ(ppm): 160.14, 142.78, 116.44, 114.08, 75.46, 31.22, 25.95 
     EXAMPLE 2 
     Adhesives were prepared by mixing neopentyl α-cyanoacrylate (NPCA) and ethyl α-cyanoacrylate (ECA) as a conventional α-cyanoacrylate in such proportions as shown Table 1 below and then incorporating therein 20 ppm of BF 3 . ethyl ether complex and 1,000 ppm of hydroquinone. Their adhesive properties are as set forth in Table 1. 
     
                       TABLE 1______________________________________  Adhesive Properties (iron/iron)Mixing Ratio    Tensile Shear                Hot Tensile(parts)  Strength    Shear StrengthNPCA/ECA (kgf/cm.sup.2)                (kgf/cm.sup.2)                             Whitening______________________________________ 1/100    70          5           Whitened(Comparativeexample)20/80     83          7           slightly                             whitened40/60     85         10           slightly                             whitened60/40    112         40           not whitened80/20    124         45           not whitened100/0    130         45           not whitened______________________________________ 
    
     EXAMPLE 3 
     Adhesives were prepared by mixing neopentyl α-cyanoacrylate (NPCA) and allyl α-cyanoacrylate (ACA) as a conventional α-cyanoacrylate in such proportions as shown in Table 2 below and then incorporating therein 20 ppm of BF 3 .ethyl ether complex and 1,000 ppm of hydroquinone. Their adhesive properties are as set forth in Table 2. 
     
                       TABLE 2______________________________________  Adhesive Properties (iron/iron)Mixing Ratio    Tensile Shear                Hot Tensile(parts)  Strength    Shear StrengthNPCA/ACA (kgf/cm.sup.2)                (kgf/cm.sup.2)                             Whitening______________________________________ 0/100   100          5           Whitened(Comparativeexample)20/80    110         12           slightly                             whitened40/60    113         23           slightly                             whitened60/40    129         45           not whitened80/20    130         45           not whitened100/0    130         45           not whitened______________________________________ 
    
     EXAMPLE 4 
     Adhesives were prepared by mixing neopentyl α-cyanoacrylate (NPCA) and 2-ethoxyethyl α-cyanoacrylate (EECA) as a conventional α-cyanoacrylate in such proportions as shown in Table 3 below and then incorporating therein 20 ppm of BF 3 .ethyl ether complex and 1,000 ppm of hydroquinone. Their adhesive properties are as set forth in Table 3. 
     
                       TABLE 3______________________________________   Adhesive Properties (iron/iron)Mixing Ratio     Tensile Shear                Hot Tensile(parts)   Strength   Shear StrengthNPCA/EECA (kgf/cm.sup.2)                (kgf/cm.sup.2)                             Whitening______________________________________ 0/100     74         5           slightly(Comparative                      whitenedexample)20/80      80         6           slightly                             whitened40/60      82         8           not whitened60/40     116        28           not whitened80/20     125        45           not whitened100/0     130        45           not whitened______________________________________ 
    
     Comparative Example 
     The adhesive properties of neopentyl α-cyanoacrylate were compared with those of n-amyl α-cyanoacrylate (n-AmCA) and iso-amyl α-cyanoacrylate (i-AmCA). The results are as set forth in Table 4. 
     
                                           TABLE 4__________________________________________________________________________                 Adhesive Properties (iron/iron)                 Tensile Hot Tensile   Chemical      Shear Strength                         Shear StrengthCyanoacrylate   Structure     (kgf/cm.sup.2)                         (kgf/cm.sup.2)__________________________________________________________________________NPCA    ##STR4##     130     45n-AmCA    ##STR5##     23      0i-AmCA    ##STR6##     68      0__________________________________________________________________________ 
    
     Testing Method 
     Tensile Shear Strength 
     Measured at 25° C. after aging 24 hours at 43±1° C., 60±2% RH, according to JIS K6861. 
     Hot Tensile Shear Strength 
     Measureds at 150° C.×1 hr after agint 24 hours at 43±1° C., 60±2% RH, according to JIS K6861. 
     Whitening 
     A schale which had been made clean was placed on black paper, and each adhesive was dropped one drop into the schale. After standing 24 hours at 43° C., 60% RH, the presence or the state of whitening was checked.