GB2314084A

GB2314084A - Toughened modified phenolic resin

Info

Publication number: GB2314084A
Application number: GB9612061A
Authority: GB
Inventors: Chen-Chi Martin Ma; Hew-Der Wu
Original assignee: National Science Council
Current assignee: National Science Council
Priority date: 1996-06-10
Filing date: 1996-06-10
Publication date: 1997-12-17
Anticipated expiration: 2016-06-10
Also published as: GB9612061D0; GB2314084B

Abstract

A toughened modified phenolic resin is prepared by mixing a phenoxy resin having a weight average molecular weight of 10,000-1,000,000 and phenol at an elevated temperature to form a glutinous mixture; mixing the glutinous mixture and an acid catalyst or catalytic electrolyte to obtain a viscous mixture having a relatively low viscosity compared to the glutinous mixture and mixing the viscose mixture and a resole type phenolic resin to form a modified phenolic resin.

Description

Toughened Modified Phenolic Resin The present invention is related to a modified phenolic resin, in particular to a modified phenolic resin which is toughened by phenoxy resin.

Conventional resins used in a pultrusion process for making a fiber reinforced resin composite are thermoset resins, such as unsaturated polyester resin and epoxy resins. Phenolic resin which is known to have excellent mechanical properties and electrical properties, especially at elevated temperatures, has been used to produce fiber reinforced products by prepreging, compounding, reaction injection molding or pultrusion processes, but phenolic resin used as a binder in the fabrication of a fiber reinforced composite product so far is still not so popular compared to the others due to its brittle nature which causes its poor coupling with fiber, its slow curing rate, and due to the side product (water) which may be generated causing void defects. Therefore there is a need in the composite industry to improve the quality and properties of a pultruded fiber reinforced phenolic based resin composite.

Several methods have been developed to toughen phenolic resin. For examples, US Patent 2,267,390 uses China wood oil (tung oil), Japanese Patent No. 29-7595 uses rosin, US Patent 2,675,335 uses alkyl phenol, US Patent 4,125,502 uses vinyl acetate and US Patent 4,157,324 uses high ortho etherified resole type phenolic resin for toughening phenolic resin. However, these methods all require the modifying agent to react with phenolic resin for a period of time in order to obtain the desired toughening effect.

At present meta-hydroxyl phenol catalyst is used to shorten the gel time of phenolic resin so that it can be used in manufacturing a fiber reinforced composite product; however, the addition of meta-hydroxyl phenol catalyst also decreases the storage stability of phenol resin and pot life of phenolic resin.

It is known that the coupling between phenol resin and the surface of a common fiber is poor, and filaments having a special surface treatment are necessary for the fabrication of a fiber reinforced phenolic resin, e.g.

filaments having a special surface treatment by isocyanate based coupling agent are available from the fiber glass manufacturers, e.g. Clark-Schwebel Fiberglass Corp., US.

These special treated filaments result in more stocks and production costs, and an additional operation procedure of changing different filaments.

Phenoxy resin is a bisphenol-A type resin preferably having the following formula (1):

wherein n is integer of at least 38, preferably 38 to 60.

Phenoxy resin unlike a common liquid type epoxy resin which has a n value lower than 15 is a solid type resin. Phenoxy resin is useful in manufacturing molded articles by an injection molding process similar to the thermoplastic resin, and can also be used as a thermoset resin by mixing a curing agent therewith.

To our knowledge there is no one in the prior art who taught or suggested using phenoxy resin to toughen phenolic resin, increase the curing rate of phenol resin without adversely affecting the storage stability thereof, and enhance the coupling between phenol resin and fiber at the same time. There is no method developed so far by which one can successfully blend the phenoxy resin in the phenolic resin.

The present inventors are the first ones to successfully develop a new technique to blend phenoxy resin in phenolic resin, whereby a modified phenolic resin having improved toughness, storage stability and interfacial coupling with other substrates is obtained.

The primary objective of the present invention is to provide a modified phenol resin toughened by phenoxy resin.

In order to achieve the objective a modified phenol resin accomplished in accordance with the present invention is prepared by the following steps: a) mixing a phenoxy resin having a weight average molecular weight of 10,000-1,000,000 and phenol, preferably in a weight ratio of phenoxy resin : phenol = 1.5 : 1 - 1 : 1, at an elevated temperature to form a glutinous mixture; b) mixing the glutinous mixture of step a) and an acid catalyst or catalytic electrolyte to obtain a viscous mixture having a relatively low viscosity compared to the glutinous mixture; c) mixing the viscose mixture of step b) and a resole type phenolic resin to form a modified phenolic resin.

It is surprising that the viscosity of the glutinous mixture in step a) can be significantly reduced by the addition of the acid catalyst. It is believed that the acid catalyst causes the phenoxy resin in the glutinous mixture to become charge-carrying, and thus enhances its solubility in the polar phenol solvent, thereby facilitating the blending of the phenoxy resin with the resole type phenolic resin.

Contemplated as the functional, or operative, equivalent to the acid catalyst for purpose of the present invention is an electrolyte having catalytic ability.

According to the present invention, there is provided a toughened modified phenolic resin prepared by a process comprising the following steps: a) mixing a phenoxy resin having a weight average molecular weight of 10,000-1,000,000 and phenol, preferably in a weight ratio of phenoxy resin phenol = 1.5 : 1 - 1 : 1, especially about 1 : 1, and heating the resulting mixture to form a glutinous mixture; b) mixing the glutinous mixture of step a) and an acid catalyst or catalytic electrolyte to obtain a viscous mixture having a relatively low viscosity compared to the glutinous mixture; c) mixing the viscose mixture of step b) and a resole type phenolic resin to form a modified phenolic resin.

Preferably, the resole type phenolic resin has a solid content of 60-75 wt and a free aldehyde content of 5-10 wtW; the amount of the acid catalyst mixed is 2-10 wtk; the amount of the phenoxy mixed is 3-25 wtk, preferably 10-15 wt%, based on the resole type phenolic resin; and the phenoxy resin has a weight average molecular weight of 10,000 to 100,000.

A suitable phenoxy resin for use in the present invention has the above formula (1) and is available from the market, which can be prepare by reacting bisphenol-A with epichloro hydrin such as epi-[1,2]-chloro-[3]propane.

The preparation of this phenoxy resin is well known in the art. Phenoxy resin has an excellent mechanical strength at room temperature. In addition, phenoxy resin has an ether linkage and hydroxyl radical, both of which can form a hydrogen bond with the phenol group of the resole type phenolic resin if the phenoxy resin is substantially mixed with the resole type phenolic resin. Therefore, the present invention not only provides a modified phenolic resin toughened by phenoxy resin but a compatible polymer blend consisting of a resole type phenol resin and phenoxy resin. The ether linkage and hydroxyl radical of the phenoxy resin can also enhance the coupling between the modified phenolic resin and a substrate when it is used as a coating composition, adhesive or binder of a fiber reinforced resin composite.

A suitable process for preparing the resole type phenolic resin is by carrying out a condensation reaction of an excess amount of formaldehyde and phenol in the presence of an alkaline catalyst. This process is well known in the art, such as the process described in US Patent 4,419,400, the disclosure of which is incorporated herein by reference.

The acid catalyst, also known as curing agent, is well known in the art, and includes the organic acid catalyst disclosed in UK patent 1,363,277, details thereof are incorporated by reference. A preferred catalyst is selected from p-toluenesulfonic acid, phenolsulfonic acid, benzoic acid and phosphoric acid. The amount of said acid catalyst used usually ranges from 2 to 10 wtk based on the weight of the resole type phenolic resin, and preferably is about 5 wt%.

A suitable phenol for use in the present invention includes (but is not limited to) phenol, ortho-cresol, meta-cresol, para-cresol, dimethyl phenol, ethyl phenol, para-phenyl phenol, para-butyl phenol, para-pentyl phenol, bisphenol-A and meta-dihydroxyl benzene.

In one of the preferred embodiments of the present invent ion, phenoxy resin and phenol were mixed and stirred at 1500C to form a glutinous material, to which p-toluenesulfonic acid was then added while stirring, and a viscose mixture having a viscosity of 200 cps (mPa.s) at 1500C was obtained. The viscose mixture was cooled to 900C while a resole type phenolic resin was being heated to the same temperature, and then they were mixed with each other and well stirred to obtain a modified phenolic resin of the present invention. This modified phenolic resin has a viscosity of 500-2800 cps (mPa.s) after being cooled to 300C, which increases to 2100-4250 cps (mPa.s) after a period of 28 hours. The viscosity was measured according to the method of ASTM D2393 with a Brookfield Viscometer.

As it is well known in the art, mineral fillers such as talc, silica, and clay, may be added into the liquid resin in order to improve the mechanical properties of the pultruded composites. The amount of said mineral fillers added usually is 10-20 wt based on the weight of the modified phenolic resin.

The present modified phenolic resin can be used at least in the fabrication of a coating composition, adhesive composition and fiber reinforced resin composite. In each of the applications, the present modified phenolic resin used generates significantly less amount of water side product during the cross-linking thereof such that the void content resulting from evaporation of water is decreased, and thus the toughness and mechanical strength of the final products are remarkably enhanced.

The invention will be further illustrated by a pultrusion process in the following Example in which parts and percentages are by weight unless otherwise indicated.

Example: I) Preparation of modified phenolic resin: The modified phenolic resin was prepared in accordance with the formulation listed in the following Table 1.

Table 1 Constituent weight (aran) 1) phenoxy resin 15 2) phenol 15 3) p-toluenesulfonic acid 5 4) resole type phenolic resin 100 1) The phenoxy resin is manufactured by Union Carbide Company, US, and has a weight average molecular weight of 23,000.

2) The phenol is a reagent grade compound and available from Japan Pure Chemicals Industrial Co. (Japan).

3) The p-toluenesulfonic acid is a reagent grade compound and available from Japan Pure Chemicals Industrial Co.

(Japan).

4) The resole type phenolic resin is a commercial phenol formaldehyde resole type resin having a solid content of 70-75 wtW and sold under a code of PF-750 from Chang Chun Plastics Co., Ltd., Taiwan.

15 g phenoxy resin and 15 g phenol were mixed and stirred under nitrogen purge at 1500C for one hour, and a miscible glutinous material was obtained. 5 g p-toluenesulfonic acid was then added to the glutinous material, the resulting mixture was thoroughly stirred for about 3 minutes, and a solution having a viscosity of about 200 cps (mPa.s) at 1500C was obtained. This solution was kept in an oven at 900C and ready for mixing with the resole type phenolic resin.

100 g of resole type phenolic resin was heated in an oven at 900C for 15 minutes, then added to the 900C solution while gently stirring, and miscible viscose solution was formed.

The aforesaid procedures were repeated except that the weight of the phenoxy resin was changed to prepare modified phenol resin products having different percentages (phr) of phenoxy resin based on the weight of the resole type phenolic resin.

II) Pultrusion: The modified phenolic resin product prepared above was placed in an impregnating tank and maintained at a room temperature of 300C. 20 rovings of 764-NT-218 glass fiber (PPG Co., US) were drawn into a bath of the impregnating resin which was maintained at 300C. 764-NT-218 glass fiber has a specific gravity of 2.54, and a single strand of this fiber has a diameter of 13.1 ym and a tensile strength of 2.2 x 105 psi (1.5 GPa). The impregnated glass fiber rovings were passed through a squeeze orifice to remove excess resin and air and through a 82-cm long, 1.27-cm wide and 0.319-cm thick curing die. Two sets of individually controlled electrical plate heaters were installed on both top and bottom of the die, where the first and the second set of plate heaters have a length of 30 cm, and a temperature of 1800C and 2000C respectively. The pulling rate was fixed at 30 cm/min. The final pultruded composite product has a fiber content of 50 vol and a specific gravity of 1.60.

III) Test specimens of the pultruded composites: The glass fiber reinforced modified phenol resin composites pultruded according to the above-described process with modified phenolic resins containing different contents of resole type phenolic resin were tested in accordance with the method of ASTM D3039, ASTM D79 and ASTM D256 to obtain their tensile strength, flexural strength and notched Izod impact strength, respectively. The results are shown in Table 2.

Table 2 Phenoxy resin content, phr 0 3 6 9 12 15 18 Tensile strength, MPa 323 451 453 572 694 669 618 Fl exural strength, GPa 571 518 531 546 548 541 595 Notched Izod impact strength, ft-lb/in 19.5 24 36 38 60 54 48 (J/cm) (10.4) (12.8) (19.2) (20.3) (32) (28.8) (25.6) The final pultruded composites were further subjected to a postcuring treatment at a temperature of 1800C for a period of one hour. The tensile strength, flexural strength and notched Izod impact strength o the postcured composites are also shown in Table 3.

Table 3 Phenoxy resin content, phr 0 3 6 9 12 15 18 Tensile strength, MPa 363 547 567 667 770 812 694 Flexural strength, GPa 693 679 697 703 706 732 660 Notched Izod impact strength, ft-lb/in 33 39 49 55.5 75 71.3 69 (J/cm) (17.6) (20.8) (26.2) (29.6) (40) (38.1) (36.8) As it can be seen from the data in Tables 2 and 3 that the tensile strength of the glass fiber/modified phenolic resin composite is enhanced when the percentage (phr) of phenoxy resin based on the weight of the resole type phenolic resin increases from 0 to 12 or 15% phr. Similar observation is also found in the flexural strength of the composites. The results show that the blending of phenoxy resin in the resole type phenol resin has a good toughening effect.

The following Table 4 lists the variation of viscosity of the modified phenolic resin products prepared above.

The viscosity was measured according to the method of ASTM D2393 with a Brookfield Viscometer.

Table 4 viscosity (cDs) (mPa.s) Storage time, h 0 8 16 24 Phenoxy resin content, phr 0 310 500 650 910 6 500 1000 1600 2100 12 1400 1900 2000 3500 18 2800 3200 3950 4250 Pure resole type phenolic resin 1400 7800 -- - * The resole type phenolic resin is a commercial phenol formaldehyde resole type resin having a solid content of 70-75 wt and sold under a code of PF-750 from Chang Chun Plastics Co., Ltd., Taiwan.

The data in Table 4 show that the viscosity of the modified phenolic resin increases with the increase of the phenoxy content thereof; however, the increasing rate of viscosity is rather low so that the modified phenol resin has a long pot life which is even longer than that of the pure resole type phenolic resin, and thus has a good storage stability.

Claims

Claims:

1. A toughened modified phenolic resin prepared by a process comprising the following steps: a) mixing a phenoxy resin having a weight average molecular weight of 10,000-1,000,000 and phenol at an elevated temperature to form a glutinous mixture; b) mixing the glutinous mixture of step a) and an acid catalyst or catalytic electrolyte to obtain a viscous mixture having a relatively low viscosity compared to the glutinous mixture; and c) mixing the viscose mixture of step b) and a resole type phenolic resin to form a modified phenolic resin.

2. A toughened phenolic resin according to Claim 1, wherein the phenoxy resin has a weight average molecular weight of 10,000-100,000.

3. A toughened resin according to Claim 1 or Claim 2, wherein the weight ratio of phenoxy resin : phenol is 1.5 : 1 to 1 : 1.

4. A toughened resin according to Claim 3, wherein the weight ratio of phenoxy resin : phenol is about 1 : 1.

5. A toughened resin according to any one of the preceding claims, wherein the resole type phenolic resin has a solid content of 60 to 75 wt% and a free aldehyde content of 5 to 10 wt%.

6. A toughened resin according to any one of the preceding claims, wherein the amount of the acid catalyst or catalytic electrolyte is 2 to 10 wt%.

7. A toughened resin according to Claim 6, wherein the amount of the acid catalyst or catalytic electrolyte is about 5 wt% based on the weight of the resole type phenol resin.

8. A toughened resin according to any one of the preceding claims, wherein the amount of the phenoxy resin is 3 to 25 wt based on the resole type phenolic resin.

9. A toughened resin according to Claim 8, wherein the amount of the phenoxy resin is 10 to 15 wt based on the resole type phenolic resin.

10. A toughened resin according to any one of the preceding claims, wherein said acid catalyst is selected from p-toluenesulfonic acid, phenolsulfonic acid, benzoic acid and phosphoric acid.

11. A toughened resin according to any one of the preceding claims, wherein said phenol is selected from phenol, ortho-cresol, meta-cresol, para-cresol, dimethyl phenol, ethyl phenol, para-phenyl phenol, para-butyl phenol, para-pentyl phenol, bisphenol-A and meta-dihydroxyl benzene.

12. A toughened resin according to any one of the preceding claims, wherein the phenoxy resin has the following formula (1)

wherein n is an integer of at least 38.

13. A toughened resin according to Claim 12, wherein n is 38 to 60.

14. A toughened resin according to Claim 1, and substantially as described in the Examples.

15. A process for preparing a toughened resin which comprises: a) mixing a phenoxy resin having a weight average molecular weight of 10,000-1,000,000 and phenol at an elevated temperature to form a glutinous mixture; b) mixing the glutinous mixture of step a) and an acid catalyst or catalytic electrolyte to obtain a viscous mixture having a relatively low viscosity compared to the glutinous mixture; and c) mixing the viscose mixture of step b) and a resole type phenolic resin to form a modified phenolic resin.

16. A process according to Claim 1, wherein the components used are as defined in any one of Claims 2 to 14.

17. A process according to Claim 15 and substantially as described in the Example.

18. The use of a phenoxy resin to toughen a phenolic resin.

19. A use according to Claim 18, wherein the phenoxy resin is as defined in any one of Claims 1, 2 and 12.

20. A use according to Claim 18 or Claim 19, wherein the phenolic resin is as defined in Claim 1 or Claim 5.

21. A use according to Claim 18, wherein the phenolic resin is toughened by a process as defined in Claim 1.

22. A use according to Claim 21, wherein said process is as defined in any one of Claims 2 to 14.

23. A coating composition formed from a toughened resin as defined in any one of Claims 1 to 14.

24. An adhesive composition formed from a toughened resin as defined in any one of Claims 1 to 14.

25. A fiber reinforced resin composite wherein the binder is formed from a toughened resin as defined in any one of Claims 1 to 14.