WO1997008230A1

WO1997008230A1 - Process for producing phenolic foams

Info

Publication number: WO1997008230A1
Application number: PCT/US1996/013387
Authority: WO
Inventors: Byron J. Hulls; Vyacheslav S. Grinshpun; Jennifer M. Willson
Original assignee: Owens Corning
Priority date: 1995-08-28
Filing date: 1996-08-19
Publication date: 1997-03-06
Also published as: AU6778596A; KR19990044126A; JPH11512131A

Abstract

This invention relates to the production of low-density resol foams from resol resins. The resol foams have a density of 9.0 pounds per cubic foot (144.166 kg/m3) or less and are produced with halogen-free hydrocarbon blowing agents such as pentane.

Description

PROCESS FOR PRODUCING PHENOLIC FOAMS

TECHNICAL FIELD This invention relates to a process for producing low-density phenolic foams having good thermal properties, high thermal retention, and good fire performance. The process uses non-ozone-depleting blowing agents.

BACKGROUND Recent awareness ofthe damage done to the ozone layer by chlorofiuorocarbons (CFCs) and to a lesser degree by their replacements the hydrochlorofluorocarbons (HCFCs), as well as the activity of these materials as greenhouse gases has raised issues of their future viability as blowing agents for foam materials. The development of non-ozone-depleting hydrofluorocarbons (HFCs) is underway, but the availability of a suitable candidate with acceptable properties at a reasonable cost is in question. A drawback of alkanes is that their thermal conductivities are inferior to the CFCs. With an increased trend towards higher energy efficiency requirements, the insulating role of foam materials is increasing in importance. Consequently, meeting these requirements with less efficient insulating gases is a major challenge to the foam production art.

Phenolic foams have been used for years as insulating materials. Their good thermal and aged thermal performance is well known. Closed-cell phenolic foams retain blowing agent gases longer and have slower air ingress than urethane, isocyanurate, and polystyrene foams. The retention of thermal conductivity over time, due to the lower permeability ofthe phenolic foam to the blowing agent and atmospheric gases, provides improved thermal insulating performance over the life span ofthe product. Phenolic materials have also been recognized as having excellent fire properties and low smoke evolution compared to other types of foam materials.

DISCLOSURE OF INVENTION We have discovered that producing phenolic foams with alkane blowing agents results in a resol foam that self extinguishes. Alkane blowing agents have a significantly higher flammability than the CFCs and HCFCs. Many currently produced foams made with nonflammable blowing agents are themselves flammable, and the use of alkanes as blowing agents for these foams will increase their flammability in the absence of flame-retardant additives. This invention is a significant improvement to the technology available in the production of low-density insulating materials with highly flammable blowing agents. The low permeability ofthe phenolic matrix provides an excellent barrier to both blowing agents and air, and yields good thermal performance even at extremely low densities. The fire performance of these materials is far superior to urethane foams made with equivalent blowing agents.

BEST MODE FOR CARRYING OUT THE INVENTION Our process includes the steps of providing a foaming composition of: (a) a phenol formaldehyde resol resin having little or substantially no free formaldehyde and having a water content of 4 to 8% and a viscosity ranging from 5,000 cps to 40,000 cps at 40°C, (b) a blowing agent, (c) a surfactant, and (d) a catalyst; mixing the composition to initiate foaming and to produce a resol foam; and curing the resol foam to a density ranging from 0.5 to 9.0 pounds per cubic foot (8.01 to 144.166 kg m³). This process allows us to foam phenol formaldehyde resins which have a high viscosity, and cure the foams to a very low density.

The blowing agents we use generally are hydrocarbons, including aliphatic and alicyclic alkanes. Preferred blowing agents are aliphatic alkanes, including pentane. Preferably, the aliphatic alkanes contain at least 4, but no more than 7 carbon atoms. Examples include pentane, hexane, heptane, isobutane, and isopentane. Unsaturated hydrocarbons such as pentene and hexene also are included.

The cycloaliphatic (or alicyclic) hydrocarbons containing at least 4, but no more than 7 carbon atoms, can be saturated or unsaturated. Illustrative saturated cycloaliphatic hydrocarbons are cyclopentane, methylcyclopentane, cyclohexane, and methylcyclohexane. Illustrative unsaturated cycloaliphatic hydrocarbons are cyclopentene, cyclohexene, and 1,3-cyclohexadiene.

Mixtures such as cyclopentane and acetone, while not preferred, also can be used. While mixtures of halogen-free hydrocarbons and CFCs and HCFCs have been suggested for foams other than resol foams, we prefer that our blowing agents for resol foams be CFC- and HCFC-free. The foams are prepared from resols which have been made using conventional starting mole ratios of phenol to formaldehyde, in the present case in the range of 1 : 1 to 1 :4.5, preferably 1 : 1.5 to 1 :2.5. The high mole ratio materials are the basis for resins which are substantially free of phenol and which can be treated with a formaldehyde co-reactant or scavenger, to reduce the initially high free formaldehyde content.

The resin is concentrated to reduce the free water content ofthe resin. A typical resin used for manufacturing resol foam has a viscosity in the order of 4,000 to 40,000 cps and a free water content of 4 to 8%. However, during the manufacture of phenolic foams from high viscosity resins in accordance with the present invention, the resin utilized will preferably have a viscosity in the order of 5,000 to 20,000 cps at 40°C.

The foamable resol mixture (resin, surfactant, blowing agent, catalyst) can be dispensed in either a batch or continuous process. In the batch process, the foamable mixture is poured into an 80°C preheated mold, enclosed, and cured in an oven at 80°C for 20 minutes. Following demolding, the foam is additionally cured for 2 hours at 80°C. In the continuous process the foamable composition is dispensed from evenly spaced tubes and nozzles onto a moving carrier sheet. Parallel lines of foam froth knit together as the froth expands to form a continuous sheet which moves through a conveyor oven at approximately 80°C. The boards are transferred to a separate oven for additional curing. The cured resol foam has a density ranging from 0.5 to 9.0 pounds per cubic foot (8.01 to 144.166 kg/m³).

Example 1 - Preparation of Resol The resol resin used in the production of these foams used a formaldehyde:phenol (F P) mole ratio of 2.3:1, using 52% formaldehyde and 99% phenol. The reaction was carried out under basic conditions at elevated temperatures with 50% caustic solution. When the Ostwald viscosity ofthe resin reached 62cst (measured at 25°C), the reaction was cooled and neutralized with 50% aqueous aromatic sulphonic acid. Urea was added as a formaldehyde scavenger at a level of 77% by mole ofthe residual formaldehyde. The resin was passed through a thin film evaporator to reduce the water content from about 30% to 4-8%. The final viscosity ofthe resin was 4,000-12,000 cps (measured at 40°C).

Example 2 - Preparation of Resol Foam We took 47.75g of a phenolic resol prepared according to Example 1 having a formaldehyde/phenol ratio of 2.3, containing 7% water and having a viscosity of 5,200 cps at 40°C and mixed it with 2.25g of a surfactant blend of 1:1 (w:w) ethoxylated alkylphenol, Harfoam PI (Huntsman Chemical Co.) and ethylene oxide-propylene oxide block copolymer Pluronic F127 (BASF). To this blend, in a cup, with stirring we added resol and surfactant. Next, we added rapidly with stirring 5g of a catalyst consisting of a blend of toluene and xylene sulfonic acids, diethylene glycol, and resorcinol. The contents ofthe cup were then transferred to a rectangular steel mold of dimensions 8x8x2 in³ 5 (203x203x51 mm³) preheated to 75°C. The mold was closed and placed into an oven preheated to 75°C. After 20 minutes, the foam was demolded and further cured at 70°C for 3 hours. Properties ofthe resultant foam are shown in Table 1. The foam had a density of 1.54 pcf (24.668 kg/m³) and had a thermal conductivity of 0.145 Btu.in/hft^F (0.021 w/m.K). After 200 days of room-temperature aging, the thermal conductivity was

10 found to be 0.164 Btu.in hft^F (0.024 w/m.K). A sample ofthe foam was placed over a laboratory Bunsen burner. When it was removed from the burner flame, the flame on the foam extinguished.

Example 3 - Preparation of Resol Foam We also blended 38.0g ofthe resol of Example 1 with 1.7g ofthe surfactant

15 in Example 2. To this was added 5. lg of n-pentane which was then stirred until the pentane was equally distributed. To the blend, we added quickly with stirring 5g ofthe catalyst material of Example 2. The resultant blend was transferred to the mold as in Example 2 preheated to 70°C. The mold was placed in an oven at 70°C for 20 minutes, demolded, and further cured at 70°C for 3 hours. The foam had a density of 1.12 pcf (17.941 kg/m³), an

20 initial thermal conductivity of 0.154 Btu.in hft^F (0.022 w/m.K), and a thermal conductivity of 0.166 Btu.in/hft^F (0.024 w/m.K) after 200 days of room-temperature aging.

Example 4 - Preparation of Resol Foam We also blended 30.0g of a blend ofthe resol of Example 1 and the surfactant in Example 2

25 at a ratio of 3.5% to the total with 5.0g of n-pentane containing 2% by mass perfluoroalkanes (3M performance fluid 5050). To this, we added rapidly with stirring 5.0g ofthe catalyst of Example 2. The resultant mix was transferred to a steel mold as described in Example 2 preheated to 80°C, and the mold was then transferred to an oven preheated to 80°C. After 20 minutes, the foam was demolded, and the foam was further cured 2 hours at

30 80°C. The foam had a density of 0.87 pcf (13.94 kg/m³) and a thermal conductivity of 0.171 Btu.in/hft^F (0.025 w/m.K). Example 5 - Preparation of Foam fcontroD We blended 20g of Alkapol SOR 490 (Rhone Poulenc) with 4g of n- pentane. To this blend, we added 20g of Mondur MR (Mobay). The mixture was fully mixed. Next, we added 4 drops of DabcoT9 (Air Products) to the mixture with stirring. The blend then was transferred from a cup to a flat sheet of aluminum foil and allowed to cure.

A sample ofthe foam was placed in a Bunsen burner flame. On removal, the foam continued to burn vigorously.

Table 1 - Test Results

Thermal Conductivity

Initial Btu.in/hft²°F

Thermal (w/m.K)

Conductivity after 200 days

Density Btu.in hft^2oF at Room

Example pcf (kg/m³) (w/m.10 Temperature Flammabilitv¹

2 1.54 (24.668) 0.145 (0.021) 0.166 (0.024) X

3 1.12 (17.941) 0.154 (0.022) 0.166 (0.024) -

4 0.87 (13.940) 0.171 (0.025) - - 5 _ -. _ 0

¹ X = material extinguishes 0 = material maintains flame

Table 1 shows that low-density resol foams can be produced with non- ozone-depleting alkane blowing agents. Both the initial thermal conductivity and the thermal performance after 200 days are excellent, illustrating the high thermal efficiency of the low-density resol foam. Furthermore, as Table 1 shows, the foam in Example 2 had excellent flame-resistant properties, extinguishing on removal of a flame source, whereas comparative Example 5, a rigid polyisocyanurate foam, continued to burn upon removal of the flame.

Claims

CLAIMS 1. A process for producing a closed-cell resol foam comprising the steps of: providing a foaming composition of (a) a phenol formaldehyde resol resin having substantially no free formaldehyde and having a water content of 4 to 8% and a viscosity ranging from 4,000 cps to 40,000 cps at 40°C;

(b) a halogen-free hydrocarbon blowing agent;

(c) a surfactant; and (d) a catalyst mixing the composition to initiate foaming and to produce a resol foam; and curing the resol foam to a density ranging from 0.5 to 9.0 pounds per cubic foot (8.01 to 144.166 kg m³).

2. A process according to claim 1 wherein the blowing agent is an aliphatic or alicyclic alkane.

3. A process according to claim 1 wherein the blowing agent contains 4 to 7 carbon atoms.

4. A process according to claim 1 wherein the blowing agent is saturated or unsaturated.

5. A process according to claim 1 wherein the blowing agent is pentane, isopentane, or cyclopentane.

6. A process according to claim 1 wherein the resol resin has a viscosity ranging from 5,000 cps to 20,000 cps at 40°C.

7. A process according to claim 1 wherein phenolic foam density ranges from 0.5 to 2.0 pounds per cubic foot (8.01 to 32.037 kg/m³).

8. A process according to claim 1 wherein phenolic foam density ranges from 0.7 to 1.8 pounds per cubic foot (11.21 to 28.833 kg/m³).

9. A low-density resol foam produced according to the process of claim 1.

10. A low-density resol foam produced according to the process of claim 5.