JPH0641507B2 - Epoxy resin powder composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to an epoxy resin powder composition, and more specifically to an epoxy resin powder composition containing an epoxy resin and a phenol-based curing agent.

[Conventional technology]

In recent years, powder compositions such as powder coatings are pollution-free, resource-saving,
As an energy-saving paint, it is being replaced by a conventional solvent-based paint over a wide range. However, since general powder coatings have a high viscosity when melted, they have the advantage of enabling thick film finishing with a single coating operation, but on the other hand, wettability with the object to be coated and penetration into details, that is, gaps. It has a drawback that it is inferior in filling property, thin film coating property, and the like, and with the expansion of applications in recent years, improvement of the above-mentioned defects as well as improvement of heat resistance and adhesiveness have been demanded. Development is needed.

On the other hand, epoxy resins come in various forms from liquid to solid, and they can be used in a wide range of fields because they can exhibit various physical properties of cured products depending on the selection of the type of curing agent used in combination with the type. Among these epoxy resins, solid bisphenol A type, bisphenol F type, novolac type epoxy resins and the like are known as those used for the above-mentioned powder coating.

However, since such a conventional epoxy resin generally has a relatively large molecular weight, it has a high melt viscosity, and when used in a powder coating, the wettability with the object to be coated, the gap filling property, and the thin film described above. It is inferior in paintability and is not suitable for adhering complex structures or filling narrow gaps. Therefore, it is conceivable to reduce the molecular weight in order to lower the melt viscosity, but it is difficult to make a powder coating. Further, in the solid bisphenol A type and bisphenol F type epoxy resins, the cross-linking density of the cured product is low due to the long chain length between the epoxy groups that are functional groups, and there is the disadvantage that the heat resistance is inferior to that of liquid resins. Adhesion is insufficient with novolac type epoxy resin.

In addition to the above, trisglycidyl isocyanurate is known as an epoxy resin which has a low molecular weight and a low melt viscosity and is solid at room temperature, but this has a drawback that the adhesive strength is extremely low. Further, when a liquid epoxy resin is used for a powder coating material, it is necessary to semi-cure for powderization, which causes a problem that the molecular weight increases and the melt viscosity increases. In addition, the same problems as described above also occur in the case of powder compositions other than powder coating materials, such as adhesives and molding materials.

[Problems to be Solved by the Invention]

The present invention pays attention to the above problems when using an epoxy resin as a powder composition, and has continued research to solve these problems, but in this research, as an epoxy resin, When a certain crystalline epoxy resin was used, it was found that a powder composition having a low melt viscosity and an excellent void filling property was obtained, and an invention based on this was completed and an application has already been filed.

On the other hand, the present inventor, while continuing research on this type of epoxy resin powder composition, especially its curing agent, identified a phenolic curing agent, which is a type of ordinary epoxy resin curing agent, as above. When used as a curing agent for a crystalline epoxy resin, particularly when a curing agent obtained by co-condensing two types of phenolic compounds having a specific group with formaldehyde is used, the synergistic action of these two groups causes remarkable moisture absorption. It was found that the anti-blocking property is improved together with the improved property. It was also found that the use of this co-condensate can eliminate the problem that when a crystalline epoxy resin is used and heat cured, it tends to cause foaming or decrease in high temperature adhesive strength. .. The present invention has been completed based on these new facts.

[Means for solving problems]

The present invention is a composition comprising a crystalline epoxy resin and a phenolic curing agent, wherein the phenolic curing agent has the formula (Where R is an alkyl group having 1 to 3 carbon atoms), and a compound (A) represented by the formula (Wherein R'is an alkyl group having 1 to 3 carbon atoms), the compound (B) is contained in a weight ratio of 30 to 80: 100.
The present invention relates to an epoxy powder composition, which is a novolac-type phenolic resin curing agent obtained by co-condensing an aldehyde with formaldehyde in a ratio such that

[Action]

The crystalline epoxy resin used in the present invention has a melting point of 50 to 50.
It is a solid crystalline epoxy resin having a temperature of 150 ° C., and so-called crystalline epoxy resin conventionally used in this kind of field can be widely used. The crystalline epoxy resin referred to here is a solid epoxy resin in which a large number of crystal peaks appear by X-ray diffraction, and has a physically sharp melting point and almost no molecular interaction at the time of melting. It has a property of extremely decreasing the viscosity. Particularly in the present invention,
An epoxy resin having a melt viscosity of 5 poise or less at a temperature higher by 10 ° C. than its melting point is preferable. Specific examples of these include, for example, 4,4'-bis (2,3 epoxypropoxy) 3,3 ', 5,5'-tetramethylbiphenyl,
Examples thereof include diglycidyl terephthalate and diglycidyl hydroquinone. More specifically, for example, diglycidyl hydroquinone represented by the following general formula (I) will be described as a representative example.

Diglycidyl hydroquinone is a compound in which the number of repeating units in formula (I) is substantially n = 0, and it has crystallinity. However, in the present invention, the above n
May be contained in an amount of about 1 to 5 or a compound in which the terminal is not epoxidized, 20% or less, preferably 5% or less.

A particularly preferred crystalline epoxy resin has the following structural formula (II) (R ″ represents H, CH ₃ or a halogen atom.) R ″ in this epoxy resin
When CH ₃ is CH ₃ , the melting point is 105 ° C. When it is melted, it exhibits a very low viscosity of about 0.02 poise at 105 ° C.

In the present invention, as the crystalline epoxy resin, one having a melting point of 50 to 150 ° C. is used as described above, but if it does not reach 50 ° C., the target powder composition causes blocking. When the temperature is higher than 150 ° C, workability tends to deteriorate. A preferable melting point is about 80 to 120 ° C.

The curing agent used in the present invention is a novolac type phenolic resin curing agent having the formula (Wherein R is an alkyl group having 1 to 3 carbon atoms), and (Wherein R'is an alkyl group having 4 to 9 carbon atoms), the compound (B) is co-condensed with an aldehyde, preferably formaldehyde. (A) and (B) at this time
And the weight ratio thereof is 30 to 80: 100.

The novolac type phenolic resin curing agent used in the present invention usually has a softening point of about 70 to 130 ° C. and a viscosity of 1 to
15 poise (melt viscosity at 150 ° C.) is preferred. At this time, if the viscosity is too low, blocking tends to occur, and if it is too high, the flowability tends to deteriorate. However, other aldehydes such as paraformaldehyde and benzaldehyde may be used in place of formaldehyde as long as the weight ratio is within the above range and the viscosity of the resin after novolak is within the above range.

As the compound (A) used in the present invention, an alkyl-substituted phenol having 1 to 3 carbon atoms is used, and it is preferable that R is CH ₃ from the viewpoint of flowability after novolac formation. Further, as the compound (B), a phenol having an alkyl group having 4 to 9 carbon atoms is used, and R'is R from the viewpoint of moisture resistance after novolac formation. Is preferred.

Further, particularly in the present invention, R is CH ₃ , R ′ is Is preferred.

In the present invention, a novolac resin obtained by co-condensing two kinds of phenols (A) and (B) with an aldehyde, especially formaldehyde is used. At this time, the compound (A) is condensed with formaldehyde and the compound ( When B) is condensed with formaldehyde and each condensate is mixed in a predetermined ratio, the co-condensation exhibits an excellent blocking resistance. Further, as compared with the case where each condensate is further co-condensed, the viscosity at the time of melting can be easily controlled and set to a low level.

The use ratio of the curing agent of the present invention is usually about 0.5 to 1.5 equivalents of the functional group of the curing agent per equivalent of epoxy group contained in the epoxy resin.

In the epoxy resin powder composition of the present invention, for example, bisphenol A type, bisphenol F type, novolak, etc. may be used together with the crystalline epoxy resin as an epoxy resin component for the purpose of adjusting melt viscosity and improving adhesive strength. Other epoxy resins such as molds can be used together. However, these other epoxy resins can be used in a proportion of 50% by weight or less in the total epoxy resin components depending on the purpose of use.

Further, in the present invention, in order to accelerate the curing, a curing accelerator suitable for the type of the curing agent to be used may be added to the powder composition, if necessary. As such a curing accelerator, conventionally known ones can be used, for example, imidazole,
Examples include tertiary amines such as imidazoline and benzyldimethylamine. However, dicyandiamide is not used in the present invention. The curing accelerator used here is usually about 0.3 to 8 parts by weight with respect to 100 parts of the epoxy resin, though it varies depending on the purpose of use of the curing agent and the like. Further, in the composition of the present invention, various additives which have been conventionally used in this kind of powdery epoxy resin composition can be used, and for example, talc, silica sand, silica, calcium carbonate, barium sulfate can be filled. Examples thereof include agents, carbon black, red iron oxide, titanium oxide, chromium oxide, pigments such as cyanine blue and cyanine green, and other flow control agents. The mixing ratio of these additives varies depending on the type and application, but is usually 0.5 to 200 parts by weight, preferably 0.5 to 50 parts by weight.

The composition of the present invention can be obtained by mixing the above components by a known means such as a dry mixing method or a melt mixing method, and pulverizing and classifying them. The particle size at this time is preferably one that passes through 30 mesh.

The composition of the present invention thus obtained has a low viscosity when melted, is excellent in gap filling properties, has good wettability with respect to an object to be coated and thin film coatability, and exhibits excellent heat resistance and adhesiveness after curing. It can be suitably used for a wide range of applications such as paints, molding materials and adhesives.

Hereinafter, the present invention will be described more specifically with reference to examples.

[Examples 1 to 5] Epoxy resin powder compositions were obtained by mixing predetermined components shown in Table 1 below in predetermined proportions, then pulverizing and classifying with a 40-mesh sieve.

[Comparative Examples 1 to 5] Compositions were prepared in the same manner as in Examples 1 to 4. However, in Comparative Examples 1 and 2, a curing agent having the same production method as that of the Examples was used, and in Comparative Examples 3 to 4, o-cresol and t-butylphenol were each independently novolacized and mixed, and Comparative Example 5 was used. o-cresol novolac resin (softening point 105 ° C)
And octylphenol novolac resin (softening point 110
(° C) was used after being co-condensed with a predetermined ratio.

With respect to the epoxy resin powder compositions of the above Examples and Comparative Examples, melt viscosity at 150 ° C., gelation time, gap filling property, foaming, high temperature adhesive strength and blocking property were measured by the following methods. The results are also shown in Table 1. The above measuring methods are as follows.

(A) Melt viscosity Temperature measured by Brookfield viscometer 150 ° C, rotor
It was measured under the conditions of No. 21.

(B) Gelation time 0.1 g of the sample powder is sprinkled on a copper plate for gelation time measurement heated to 150 ± 1 ° C. and stirred with a needle tip. The time from when all of the sample powder was melted until stirring with a needle became impossible was measured with a stopwatch, and was taken as the gelation time.

(C) Gap filling rate Two 0.5 mm thick spacers are sandwiched between two steel plates with a width of 15 mm, a length of 100 mm and a thickness of 1.0 mm at intervals of 10 mm, and the steel plates are heated to 150 ° C. At that time, the powder composition is sprinkled into the slit-shaped gap formed between the steel plates and the spacers, the melt is poured, and then the powder composition is held at 180 ° C. for 30 minutes to be cured at room temperature. The shear adhesive strength was measured after cooling to room temperature, and indicated as the ratio (%) of the shear adhesive strength measured by this method to the shear adhesive strength at room temperature by the conventional method.

(D) Foaming 3 g of powder was sprayed on a steel plate heated to 180 ° C. and cured, and the presence or absence of foaming of the cured product was examined.

(E) High temperature adhesive strength The shear adhesive strength of the shear adhesive strength test piece obtained by the usual method was measured in an atmosphere of 150 ° C.

(F) Blocking resistance When about 50 g of the powder composition was squeezed with a hand, it was examined whether or not it became a lump.

However, the epoxy resin- (I) and the epoxy resin- (II) used in Table 1 above are as follows.

Epoxy resin- (I): (However, n is 0.3) Epoxy resin- (II): [Effect] As is clear from Table 1 above, the composition of the present invention is excellent not only in the gap filling property but also in the foaming property and the sag.

Further, although not particularly shown in Table 1, it is extremely excellent in moisture absorption resistance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takahira et al., 1-2, Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denki Kogyo Co., Ltd. (56) Reference JP-A-61-261371 (JP, A) JP Sho 62-70416 (JP, A) JP-A 63-227622 (JP, A)

Claims (1)

[Claims] 1. A composition comprising a crystalline epoxy resin, a phenolic curing agent, and optionally a curing accelerator (except dicyandiamide), wherein the phenolic curing agent is of the formula (Where R is an alkyl group having 1 to 3 carbon atoms)
(A) and formula (Where R'is an alkyl group having 4 to 9 carbon atoms)
Epoxy resin powder, which is a novolac-type phenolic resin curing agent obtained by co-condensing (B) with aldehyde in a ratio of (A) :( B) of 30 to 80: 100 by weight. Body composition.