EP0073191A4

EP0073191A4 - Heat stable molded phenolic resin article.

Info

Publication number: EP0073191A4
Application number: EP19810901736
Authority: EP
Inventors: Michael Dean Bertolucci; John Rudolf Bartolomucci
Original assignee: Plastics Engineering Co
Current assignee: Plastics Engineering Co
Priority date: 1981-03-02
Filing date: 1981-03-02
Publication date: 1983-08-23
Also published as: EP0073191A1; BR8108979A; JPS58500568A; WO1982003080A1

Abstract

A heat stable molded phenolic resin article comprising, in percent by weight, from about 20 to about 70 percent of a phenolic resin, from about 3 to about 25 percent of an acrylonitrilebutadiene elastomer, and from about 15 to about 70 percent of a silicate mineral. Also a molding composition comprising, in percent by weight, from about 20 to about 70 weight percent of a phenol-aldehyde thermosettable resin, from about 3 to about 25 weight percent of an acrylonitrilebutadiene elastomer, and from about 15 to about 70 weight percent of silicate mineral.

Description

HEAT STABLE MOLDED PHENOLIC RESIN ARTICLE

This application relates to thermoset plastics and to thermosetting plastic compositions. More particularly, it relates to a molded thermoset article containing a phenol-aldehyde resin, an acrylonitrile-butadiene copolymer, and a silicate mineral in fiber or particulate form; and to thermosetting molding compositions containing a thermosettable phenol-aldehyde prepolymer, an acrylonitrile-butadiene copolymer and a silicate mineral in fiber or particulate form.

BACKGROUND OF THE INVENTION

Phenolic-aldehyde resins are generally highly brittle low impact strength products of limited compatibility with other plastics. Plasticizers have been employed with these products to increase the flexibility, but increased flexibility has resulted in the diminution of other properties and processing difficulties. For example, to obtain any significant degree of flexibility relatively large amounts of up to or more than equal parts of glycols or glycerine must be used which diminishes the product strength and induces sweating out of the glycol and glycerine during the heat curing cycle. Further, plasticization by crosslinking with unsaturated thermoplastic polymers like polyvinylbutyral or compatible elastomers has not bees wholly satisfactory because of the lowered heat and solvent resistance of the resulting mixtures. These mixtures have improved impact strength, but still lack suitable flexibility. Furthermore, unsaturated oils like tung oil, even in substzntial amounts as resin modifiers, fail to provide sufficient flexibility.

The inclusion of finely divided fillers such as wood flour and walnut shell flour in these products adversely affects their heat resistance, dimensional stability and does little to improve impact strength. When the molded product contains long fibered fillers such as paper flock, cotton flock or sisal fiber, it has adequate impact strength but remains deficient in heat resistance and dimensional stability. Also, the surface qualities of the molded product are unsatisfactory for many applications.

Thus, there is a need for a molded product made from phenolic-aldehyde resins which has good impact strength, good heat resistance, good dimensional stability, good hot rigidity, high flexural modulus, good surface appearance, and good heat stability, i.e., the ability to retain its properties upon exposure to heat. The present invention provides such a molded article and a molding composition for making such an article.

DESCRIPTION OF THE INVENTION The present invention is based on the discovery that a phenolic molded article containing a phenolic resin, an acrylonitrile-butadiene copolymer, and a silicate mineral, either in partieulate or fiber form, possess good impact strength, good heat resistance, good dimensional stability, good hot rigidity, high flexural modulus, good surface appearance, and good heat stability.

Thus, one embodiment of this invention is a phenolic molded article containing a phenolic resin, an acrylonitrilebutadiene copolymer, and a silicate mineral. Another embodiment of the present invention is a phenolic molding composition containing a phenolic thermcsettiag resin, an acrylonitrilebutadiene copolymer, and a silicate mineral.

The molded article of the present invention comprises from about 20 to about 70 percent by weight of a phenolic resin. The phenolic resin may be a one- or two-stage phenolic resin. The two-stage phenolic resins, the novolak resins, are well known and may in general be the condensation product of a phenol, such as phenol itself, the cresols, xylenols, cresylic acid or resorcinol or mixtures thereof, and an amount of an aldehyde such as formaldehyde, acetaldehyde, furfural and the like insufficient to cause complete crosslinking, or cure, and in which an acid or basic catalyst may be used to promote the reaction. The thermosettable resin produced by this reaction is mixed with an amount of curing agent, such as hexamethylenetetramine, to cause the mixture to harden and cure to an infusible, insoluble state when subjected to heat or to heat and pressure. Such a resin might be, for example, the reaction product of phenol and formaldehyde in the ratio of 0.85 mole of formaldehyde per mole of phenol, with sulfuric acid as the catalyst. The thermosettable resin so produced may then be mixed with hexamethylenetetramine, for example, in the ratio of 16 parts by weight of hexamethylenetetramine per 100 parts by weight of the novolak resin, to produce the final resin capable of being completely cured under beat or heat and pressure.

Typical of the two-stage resins suitable for use in the present invention are those prepared by placing one mole of phenol into a reactor with 1% by weight concentrated sulfuric acid and heating to a temperature of 97º-100ºC. While maintaining the temperature, 0.75 mole of formaldehyde as a 37% aqueous solution is slowly added, over a period of 30-60 minutes, using heat and vacuum, the reaction product then is dehydrated until a temperature of 120º-130ºC is reached at 27-28 inches of vacuum. The resin product is then cooled and ground with 14-18 parts by weight of hexamethylenetetramine per 100 parts by weight of resin with the resulting ground mixture being typical of the two-stage molding resin useful in the composition of this invention. The one-stage phenolic resins, the resole resins, are well known and may in general be the condensation product of a phenol, such as phenol itself, the cresol's, xylenols, cresylic acid or resorcinol or mixtures thereof, and an amount of an aldehyde such as formaldehyde, acetaldehyde, furfural and the like, which is sufficient to cause crosslinking or cure-when subjected to heat or heat and pressure. An alkaline catalyst may be used to promote the reaction. The product of this reaction is thermosetting without the addition of hardening or curing agents. An illustrative example of the production of a one-stage resin is the reaction of phenol with formaldehyde in the ratio of 1.5 moles of formaldehyde per mole of phenol, with caustic soda 'as the catalyst.

Exemplifying the one-stage resins found suitable for the present invention are those prepared by reacting one mole of phenol with a solution of formaldehyde in the presence of a 0.5-2 percent by weight based on the phenol of a hydroxide catalyst (sodium, calcium, barium, etc.) to yield a ratio of 1.0 to 1.3 moles of formaldehyde to one mole of phenol. The reaction is carried out by heating slowly (30-60 minutes} to a temperature of 70º-100ºC and holding at that temperature for another 30-60 minutes to carry out the condensation step. The resin product is recovered by dehydrating while heating under vacuum and then cooling.

The phenol resin component is present in the molded article in amounts generally ranging from about 20 to about 70 weight percent, preferably from about 25 to about 55 weight percent, more preferably from about 30 to about 50 weight percent, and most preferably from about 35 to about 45 percent by weight. The acrylonitrile-butadiene elastomers which are used as essential constituents of the molded articles are well known and are generally the eopolymerization products of acrylonitrile and butadiene monomers. Preferred acrylonitrile-butadiene copolymers are those formed from butadiene and acrylonitrile monomers wherein the weight ratio of butadiene monomers to acrylonitrile monomers is in the range of from about 95:5 to about 15:85. Generally, the acrylonitrile-butadiene constituent is present in the molded article in from .about 3 to about 25 percent by weight, preferably from about 4 to about 20 weight percent by weight, more preferably from about 5 to about 15 percent by weight, and most preferably from about 8 to about 12 percent by weight.

The silicate minerals which are used as essential constituents of the molded article ar e also well known and are selected from glass, both glass fibers and particulate glass, the alkali and alkaline earth metal silicates, aluminum silicate, and mixtures thereof. Illustrative of the alkali and alkaline earth metal silicates are sodium silicate, potassium silicate, magnesium silicate, calcium silicate and lithium silicate. The silicate mineral constituent may comprise only one silicate mineral, i.e., glass, or a mixture of two or more silicates, i.e., glass and calcium silicate or calcium silicate and aluminum silicate. One particularly useful silicate constituent contains a mixture of glass and calcium silicate in a weight ratio of 1:1. A particularly useful calcium silicate is a silane modified calcium silicate which contains a minor amount, i.e., from about 0.5 to about 2 weight percent, of silane and a major amount, i.e., from about 93 to about 99.5 weight percent, of calcium silicate. Generally, the silicate mineral constituent is present in the molded article in from about 15 to about 70 weight percent, preferably from about 20 to about 65 weight percent, more preferably from about 30 to about 60 weight percent, and most preferably from about 40 to 50 weight percent.

The molded article may also optionally include other materials such as dyes, pigments, fillers, lubricants and the like, all of which are well known in the art.

In the practice of the instant invention, the acrylonitrile- butadiene copolymer and the silicate mineral are added to the phenol-aldehyde resin prepolymer prior to the compounding of the resin into a molding composition. Generally, in the case wherein the novolak resin is used as the resin component. of the molded article, the phenol and aldehyde are first reacted in the presence of heat and a catalyst to form a prepolymer; the prepolymer is ground and a suitable curing agent, such as hexamethylenetetramine, is added thereto; the mixture of the curing agent and prepolymer is further ground to powder form; the powdered mixture of prepolymer and curing agent is then mechanically mixed, in an extruder or roll system, with the acrylonitrile-butadiene copolymer and silicate mineral to form the molding composition; and this molding composition is fed into a molding apparatus wherein, by the application of heat, the prepolymer is cured to the phenol novolak resin. Another method of making the novolak resin containing molded article comprises using a liquid phenol-aldehyde prepolymer. In this process, the liquid prepolymer obtained by reacting the phenol and aldehyde in the presence of a catalyst and heat is blended with a curing agent with the silicate mineral and acrylonitrile-butadiene copolymer, in an extruder or roll system, to form the molding composition; and the molding composition is fed to a molding apparatus wherein the orepolymer is cured, by the application of heat, to the ahenol novolak resin. Generally, in the case wherein the resole resin is used as the phenolic resin component of the molded article, the phenol and aldehyde are partially reacted in the presence of heat and a catalyst to form, a prepolymer. The prepolymer is then ground to powder form; the powdered prepolymer is then mechanically mixed, in an extruder or roll system, with the silicate mineral and the acrylonitrile-butadiene copolymer to form a molding composition; and this molding composition is then molded in a molding apparatus wherein the prepolymer is cured, through the application of heat, i.e., further condensed and crosslinked, to form the phenol resole resin.

It is understood, however, that the method of preparing the composition of this invention is not critical and can vary depending on the desired method to be employed or the form of the composition herein claimed.

When the term prepolymer is used herein, it is meant to include the further curable, i.e., further crosslinkable or thermosettable, partial condensation product of a phenol and an aldehyde. In the case of the resole prepolymer, curing or thermosetting occurs by further application of heat to the partial condensation product of a phenol and an aldehyde. In the ease of a novolak prepolymer, further curing or thermosetting occurs by heating the partial condensation product of a phenol and aldehyde in the presence of a curing agent such as hexamethylenetetramine.

Thus, another embodiment of the present invention comprises a molding composition comprising a prepolymer of a phenolic resin. specifically a prepolymer of a novolak or resole resin, an acrylonitrile-butadiene copolymer, and a silicate mineral. The phenolic resin prepolymer component is present in the molding composition in amounts generally ranging, in percent by weight. the prepolymer is cured, by the application of heat, to the phenol novolak resin.

Generally, in the case wherein the resole resin is used as the phenolic resin component of the molded article, the phenol and aldehyde are partially reacted in the presence of heat and a catalyst to form a prepolymer. The prepolymer is then ground to powder form; the powdered prepolymer is then mechanically mixed, in an extruder or roll system, with the silicate mineral and the acrylonitrile-butadiene copolymer to form a molding composition; and this molding composition is then molded in a molding apparatus wherein the prepolymer is cured, through the application of heat, i.e., further condensed and crosslinked, to form the phenol resole resin.

When the term prepolymer is used herein, it is meant to include the further curable, i.e., further crosslinkable or thermosettable, partial condensation product of a phenol and an aldehyde. In tha ease of the resole prepolymer, curing or thermosetting occurs by further application of heat to the partial condensation product of a phenol and an aldehyde. In the ease of a novolak prepolymer, further curing or thermosetting occurs by heating the partial condensation product of a phenol and aldehyde in the presence of a curing agent such as hexamethylenetetramine.

Thus, another embodiment of the present invention comprises a molding composition comprising a prepolymer of a phenolic resin, specifically a prepolymer of a novolak or resole resin, an acrylonitrile-butadiene copolymer, and a silicate mineral. The phenolic resin prepolymer component is present in the molding composition in amounts generally ranging, in percent by weight, from about 20 to about 70 percent, preferably from .about 25 to about 55 percent, more preferably from about 30 to about 50 percent, and most preferably from about 35 to about 45 percent. The acrylonitrile-butadiene copolymer component of the molding composition is generally present, in percent by weight, from 3 to about 25 percent, preferably from about 4 to about 20 percent, more preferably from about 5 to about 15 percent, and most preferably from about 8 to about 12 percent. The silicate mineral component of the molding composition is generally present, in percent by weight, in from about 15 to about 70 percent, preferably from about 20 to about 65 percent, more preferably from about 30 to about 60 percent, and most preferably from about 40 to about 50 percent.

The molding composition may also optionally include other materials such as dyes, pigments, fillers, lubricants and the like, all of which are well known in the art. The molding compositions are molded into various shapes using conventional molds, molding conditions and techniques of operation. PREFERRED EMBODIMENT OF THE INVENTION

In order to more fully and clearly illustrate the present invention, the following examples are presented. It is intended that the examples be considered as illustrative rather than limiting the invention disclosed and claimed herein. In the examples, all parts and percentages are on a weight basis unless otherwise specified.

EXAMPLE 1

This example illustrates a molded article outside the scope of the instant invention molded from a molding composition containing a typical two-stage phenolic thermosetting molding resin and silicate minerals but not containing the acrylonitrile-butadiene copolymer. The formulation employed was as follows: Percent by Weight

Resin 40

Silicate Minerals (a 1:1 weight 56. 5 ratio of glass to silane modified calcium silicate}

Lubricants 1.5 Colorants 2. 0 -

The above ingredients were comixed on a conventional roll-mill system and molded into test samples using a pressure of about 1,000 psi and a temperature of about 165ºC for about one minute.

EXAMPLE 2 This example illustrates a molded article outside the scope of the instant invention molded from a molding composition containing a typical two-stage phenolic thermosetting molding resin and acrylonitrile-butadiene copolymer but not containing the silicate minerals. The formulation employed was as follows:

Percent by Weight Resin 40

Acrylonitrile-butadiene Copolymer 10 Cellulosic Filler 46.5

Lubricants 1.5

Colorants 2.0

EXAMPLE 3 This example illustrates a molded article outside the scope of the instant invention molded from a molding composition containing a typical two-stage phenolic thermosetting molding resin and the silicate minerals but containing Elvaloy (an ethylene vinyl acetate copolymer sold by E.I. DuPont de Nemours and Company) in place of the acrylonitrile-butadiene copolymer. The formulation employed was as follows: Percent by Weicht

Resin 40

Elvaloy (ethylene vinyl 10 acetate) 46.5

Silicate Minerals (a 1:1 weight ratio of glass to silane modified calcium silicate)

Lubricants 1.5

Colorants 2.0

The above ingredients were comixed on a conventional roll-mill system and molded into test samples using a pressure of about 1,000 psi and a temperature of about 165ºC for about 1 minute.

EXAMPLE 4 This example illustrates a molded article of the present invention molded from a molding composition containinc a typical two-stage phenolic thermosetting molding resin, acrylonitrile-butadiene copolymer, and the silicate minerals. The formulation employed was as follows:

Percent by Weicht

Resin 40

Aerylonitrile-butadiene 10 Copolymer

Silicate Minerals (a 1:1 weight 46.5 ratio of class to silane modified calcium silicate)

Lubricants 1.5

Colorants 2.0

The above ingredients were comixed on a conventional roll-mill system and molded into test samples using a pressure of about 1,000 psi and a temperature of about 165ºC for about cse minute.

The properties of the molded products of Examples 1-4 were compared and the comparative results are set forth in fable I.

Several test specimens comprising a 4 inch diameter by 1/3 inch thick disc were subjected to a Drop Ball Imoact Test. In this test, the disc was placed in a dropped ball impact tester and the center of the disc was struck with a 1/2-pound weight. The weight was dropped repeatedly from a height sequentially raised in 1-inch increments and the point at which the specimen shattered was recorded.

Several test specimens one-half inch wide and one-half inch thick were subjected to the Izod impact test. The Izod impact test was performed in accordance with the ASTM standards D256-A. Briefly, the specimen is notched and placed in a holder and a fixed pendulum swings down and breaks the sample. The value of the energy expended in breaking the specimen expressed in ft. lbs. /in. of notch is recorded.

Several test specimens comprising a transfer molded 1/2" × 1/2" × 5" bars were subjected to the Bar Impact Test. In this test, the bar was placed in a fixture supporting the bars at their ends and the center of the bar was struck with a 1/2-pound Gardner-type dart. The dart was raised in 2 inch increments after each strike and the point at which the specimen cracked was recorded.

Several test specimens 1/4" × 1/2" × 5" were tested for flexural strength, both before and after heat aging, according to ASTM standard D-790.

The results of these tests are set forth in Table I.

Table I

Test Formulation (EXAMPLE) 1 2 3 4

Drop Ball Impact {1/2 Ib.wt.) as molded 15" 8" 24" 25" 5 hrs./350ºF post baked 12" 9" 26" 24"

Bar Impact (1/2 lb.wt.) as molded 18.9" - - 29.6" 5 hrs./350ºF post baked 15.2" 37.7"

Notehed Izod (ft.lb./in.) as molded 0.45 0.38 0.52 0.60 5 hrs./350ºF post baked 0.40 0.48 0.53 0.60

Unnotched Izod (ft. lb./in.) as molded 1.7 1.7 2.1 2.7

Heat Distortion Temperature ºF at 264 psi 410º 348º 363º 550º+

Flexural Strength (psi) as molded 15,200 8,000 10,900 12,200

5 hrs./350ºF post baked 17,770 9,500 11,000 15,300 5 hrs./350ºF & 48 hrs./ 16,530 6,000 9,100 17,850

450ºF post baked

As can be seen from Table I, phenolic molded articles containing both the acrylonitrile-butadiene copolymer and the silicate mineral exhibit an increase in impact strength, heat distortion temperature, and flexural strength after exposure to heat, over those phenolic molded articles which do not contain the combination of both the acrylonitrile-butadiene. copolymer and silicate mineral.

It can be seen from Table I that while the flexural strength of a phenolic molded article of the instant invention, i.e., one containing both the crylonitrile-butadiene copolymer and the silicate mineral, continues to increase after exposure to heat, the flexural strengths of the prior art phenolic molded articles, i.e., articles of Examples 1-3, tend to first increase after mild heating but then decrease after exposure to more severe heating conditions. Thus, while the initial flexural strength of the molded article of Example 1, which contains the silicate mineral but not the acrylcnitrile-buradiene copolymer, is greater than the initial flexural strength of the molded article of Example 4, which contains both the acrylonitrile-butadiene copolymer and the silicate mineral, the flexural strength of the article of Example 4 continually increases upon exposure to heat until after being heated for 5 hours at 350ºF and for an additional 43 hours at 450 ºF, it is greater than both the initial and identically heat aged flexural strengths of the article of Example 1.

Table I clearly illustrates the criticality of the presence of both the acrylonitrile-butadiene copolymer and the silicate mineral in obtaining a phenolic article having improved properties, particularly improved heat stability.

Although the above examples have shown one embodiment of the present invention, variations thereof are possible in light of the above teachings. It is, therefore, to be understood that changes may be made in the particular embodiments of the invention described which are within the full intended scope of the invention as defined by the appended claims.

Claims

1. A heat stable molded article comprised of, in percent by weight, (i) from about 20 to about 70 percent of a phenolic resin; (ii) from about 3 to about 25 percent of an acrylonitrile-butadiene copolymer; and, (iii) from about 15 to about 70 percent of a silicate mineral.

2. The article according to Claim 1 wherein the phenolic resin is the condensation product of a phenol and an aldehyde.

3. The article according to Claim 1 wherein said aldehyde is formaldehyde.

4. The article according to Claim 2 wherein said phenolic resin is a novolak resin.

5. The article according to Claim 2 wherein said phenolic resin is a resole resin.

6. The article according to Claim 2 wherein said silicate mineral is selected from the group consisting of glass, the alkali and alkaline earth metal silicates, aluminum silicate, and mixtures thereof.

7. The article according to Claim 2 wherein said silicate mineral is a mixture of glass and silane modified calcium silicate.

8. The article according to Claim 2 wherein said acrylonitrile-butadiene copolymer is the copolymerization product of acrylonitrile and butadiene monomer.

9. The article according to Claim 8 wherein the weight ratio of the butadiene monomers to the acrylonitrile monomers is from about 95:5 to about 15:85.

10. The article accordinα to Claim 2 wherein said article contains inert additives.

11. The article according to Claim 10 wherein said additives are lubricants and colorants.

12. A molding composition comprising: (i) from about 20 to about 70 weight percent of a thermosettable phenol-aldehyde resin; (ii) from about 3 to about 25 weight percent of an acrylonitrile-butadiene copolymer; and, (iii) from about 15 to about 70 weight percent of a silicate mineral.

13. The composition according to Claim 12 wherein said thermosettable phenol-aldehyde resin is the partial, further curable, condensation product of a phenol and an aldehyde.

14. The composition according to Claim 13 wherein said aldehyde is formaldehyde.

15. The composition according to Claim 13 wherein said thermosettable phenol-aldehyde resin is a thermosettable novolak resin.

16. The composition according to Claim 13 wherein said thermosettable phenol-aldehyde resin is a thermosettable resole resin.

17. The composition according to Claim 13 wherein said silicate mineral is selected from the group consisting of glass, the alkali and alkaline earth metal silicates, aluminum silicate, and mixtures thereof.

18. The composition according to Claim 17 wherein said silicate mineral is a mixture of glass and silane modified calcium silicate.

19. The composition according, to Claim 13 wherein said acrylonitrile-butadiene copolymer is the copolymerization product of acrylonitrile and butadiene monomers.

20. The composition according to Claim 18 wherein the weight ratio of the butadiene monomers to the acrylonitrile monomers is from about 95:5 to about 15:35.

21. The composition according to Claim. 13 wherein said composition contains colorants and lubricants.