GB2141455A - Flame-resistant core stock - Google Patents

Abstract

A flame-resistant paper useful in forming decorative and industrial laminates free of asbestos comprising a web formed from an inorganic non-combustible filler, an organic fiber and optionally a binder and a non- combustible fiber, wherein the web is impregnated with a resin such as a phenol-formaldehyde resin or an amine-formaldehyde resin. The aforesaid paper is typically laminated with other layers of the same or different paper and used as core stock, decorative and/or paper to provide products useful for a wide variety of applications in the decorative and industrial laminating field where flame resistance is required.

Description

SPECIFICATION Flame-Resistant Core Stock The present invention is directed to a paper having among its utilities the formation of flame resistant laminates.

A standard decorative laminate consists of a core of several laminated paper sheets impregnated with phenolic resin and decorative and overlay sheets of paper impregnated with melamine formaldehyde resin. These laminates have a wide variety of uses including as a veneer for desks, tables and other furniture and as wall covering. They are often used in ship and aircraft interiors where is it particularly important that they be fire resistant so as to prevent the spread of fire in an emergency.

One practice that frequently has been used in the past to make flame-resistant decorative laminates is to form the core Iaminae from an asbestos fiber stock. In cases where asbestos is undesirable, various efforts have been directed to developing a flame-resistant asbestos-free core stock. U.S. Patent No. 3,383,267 to Sunden (1968) and U.S. Patent No.3,647,595 to Sunden (1972) disclose a core stock formed by impregnating kraft paper with phenol formaldehyde resin containing an aminephosphate salt as a flame retardant. U.S. Patent No.4,288,491 to Surzhenko et al (1981) discloses a core stock similar to that of Sunden wherein the flame retardant is the reaction product of an aluminum of copper compound with phosphoric acid and nitrogen bases.

Previous core stocks have a number of disadvantages. In some cases the combustibility index of the core stock may be too high. The fire code of the U.S. Coast Guard is one of the most stringent in the industry. In other cases, the capacity of the web forming the core stock for the impregnating resin (pick up) may not be sufficient to form an adherent tightly bound laminate. One particularly disadvantageous feature of most prior core stocks is that the composition from which the web is formed is not compatible with standard papermaking procedures so as to facilitate fabrication of the core stock.

Thus, one object of the present invention is to provide a flame-resistant paper with the required physical and mechanical properties (e.g., strength, absorbancy, heat and flame resistance, etc.) and which is more compatible with established papermaking practices.

The present invention provides a paper comprising a web impregnated with a resin wherein the web is characterized in that it is formed from about 1 5 to 90% of a noncombustible inorganic filler, about 5 to 30% of an organic fiber, and up to about 20% of a binder.

Unless otherwise indicated all percentages are by dry weight. In accordance with a preferred embodiment, up to 30% of a noncombustible fiber is added to the web composition to impart burn out strength to the paper. The aforesaid paper can be used in forming decorative laminates as one or more layers of the core stock or as a decorative sheet. It has been found that the paper of the present invention has acceptable printing properties especially after it has been calendered.

The present invention also provides laminates wherein the aforesaid paper comprises at least one layer of the laminate and, more preferably, at least one of the surface layers or one of the layers which immediately underlies the decorative and/or overlay sheets.

The inorganic filler component of the paper of the present invention may be any noncombustible inorganic granule which improves the fire-resistant properties of the stock.

Representative examples include all types of clays (e.g., bentonite and kaolin clays), wollastonite, talc, silica, alumina, mica, hydrated alumina, vermiculite (preferably exfoliated), diatomite, etc.

Among these mica alone or mica in combination with vermiculite are preferred. The combination of mica and vermiculate is advantageous because it gives good control over density and absorbancy.

The inorganic filler must have a particle size which can be homogeneously dispersed in the pulp and retained by the paper. Vermiculate granules may range from powder size to coarse grains, e.g., from about 8 mesh down to 100% through 100 mesh. Larger grain vermiculite can be used if the filler is aground to smaller particle sizes upon forming the pulp. Smaller particle vermiculite tends to undesirably reduce water absorbancy. The particle size of the mica is less critical than that of vermiculite and can range from 100% through 50 mesh to 100% through 325 mesh. Best results have been achieved using 200 mesh mica and No. 4 vermiculite (6090% larger than 50 mesh).

The a-mount of inorganic filler in the paper can be adjusted throughout a range of from about 1 5 to 90% depending upon the fire code specifications which must be satisfied. Similarly the amount of organic fiber in the paper can be adjusted in the range of about 5 to 30%. Irigeneral the amounts of filler and organic fiber are coordinated to adjust the balance between flame resistance and strength. At filler contents on the order of 90%, the paper is highly flame-resistant but exhibits low tensile strength. As the amount of organic fiber is increased, the strength of paper improves but flame-resistance declines due to the higher content of organic matter in the stock. For most applications it has been found desirable to use about 9 to 20% organic fiber with about 75 to 85% filler.

Substantially any organic fibrous material commonly used in making water laid fibrous webs or sheets can be used in making the paper of the present invention. Representative examples of useful fibers include cellulosic fibers and synthetic organic fibers such as acrylics, regenerated cellulose, polyesters, phenolics and the like.

Cellulosic fibers having fine, strong fibers providing good strength and retention characteristics are preferred such as those obtained in a northern softwood kraft pulp.

It is also desirable to include inorganic fibers in the paper to enhance burn out strength; that is to prevent a laminate of the paper from crumbling when the organic component has been combusted. Glass fibers are the inorganic fiber of preference, but ceramic fibers, zirconia-silica fibers, crystalline alumina whiskers, alumina silicate fibers, metal filaments, etc. may also be useful. These fibers may be used in the web in amounts up to 30% and need not be included if burn out strength is not important. Generally, the fibers used range from about 0.5 to 1 cm in length and about 8 to 12 microns in diameter.

Larger fibers are more difficult to disperse and smaller fibers are more costly.

A binder is optional but included in the web forming composition to add strength and to retain the filler so that it is not lost during fabrication.

Any of the common, preferably flame-resistant, latexes and binders conventionally used in papermaking can be used in the present invention. Some representative examples of flame-resistant binders and latexes include halogen-containing organic polymers such as polyvinylidene chloride, polyvinyl chloride, ethylene vinyl chloride copolymer, neoprene, and copolymers of the monomers forming the aforesaid polymers with vinyl acrylae, vinyl acetate, styrene, butadiene, acrylonitrile, etc.

Polyvinylidene chloride is most preferred.

Representative examples of suitable but nonflame-resistant binders include starch, polyvinyl alcohol copolymer, acrylic polymers, ethylenevinyl acetate copolymers, styrene-butadiene rubber, acrylonitrile-butadiene rubber, natural rubber and the like.

The amount of binder is not particularly critical.

It is usually employed in an amount up to about 20% (solids). If the paper is prepared without a binder it is desirable to use more organic fiber for additional strength (e.g., about 20 to 50%).

The paper of the present invention is manufactured using conventional paper or millboard production techniques. Broadly the steps used in forming the web are: (i) mixing the furnish ingredients (i.e., fiber, mica, and binder) in standard papermaking beaters, pulpers or stock chests; (ii) forming the web on a standard wet cylinder machine, cylinder board machine or Fourdrinier machine; and (iii) drying the web in conventional drying ovens or drums. Where the web is to be printed, it is preferably calendered. It may be desirable to refine the organic fiber material prior to adding the inorganic filler since after the inorganic filler has been added there can be equipment wear and stock handling problems.

One practice that has been used is to add the glass fiber to the refined cellulose fiber and blend the fiber with the filler and binder in a stock chest.

The pulp is usually mixed such that it has a consistency of about 1% when it is put on the paper machine. Alum, retention aids, wet strength resins and/or other additives can be added to the paper composition in a conventional manner depending on the properties desired.

The capacity of the web for the impregnating resin (absorbency) can be adjusted by controlling various factors such as the nature of the filler, the extent to which the web is pressed and the degree to which the cellulosic fibers have been refined. It is desirable for most applications to manufacture a paper having a resin capacity of about 25 to 60% based on the total weight of the resin impregnated paper. If the resin capacity is too low a laminate formed from the paper may not have good structural integrity. Higher resin capacity is functional but unnecessary and a waste of resin in many cases.

The desirable resin capacity depends on whether the paper is used as a core lamina or as a decorative or an overlay lamina. When impregnating with phenol formaldehyde resin, 25 to 35% resin solids in the impregnated paper is desirable for core lamina. When impregnating with melamine-formaldehyde resin, 50 to 55% may be desirable for a decorative sheet. It may be desirable to use other resins under different conditions.

Preferably, the papers of the present invention provide a resin penetration rate less than about 40 seconds when they are the thickness of core stock and less than about 20 seconds when they are the thickness of decorative sheets. This rate is measured by floating a sample of the paper on a reservoir of resin (e.g., a solution of Monsanto 841 in water and methanol (50:50) having a viscosity of 92 cps) at 250C and measuring the time it takes the paper to wet through.

The web can be impregnated with any of the resins conventionally used as impregnating resins in forming flame-resistant decorative laminates.

The resin is used for interlaminar strength and to provide a hard wear-resistant material. Either thermosetting or thermoplastic resins may be used. Representative examples of thermosetting resins suitable for use in the present invention are phenol-formaldehyde resins, amine-formaldehyde resins, urea-formaldehyde resins, melamineformaldehyde resins as well as epoxy resins, polyester resins, vinyl acetate copolymers, acrylic resins and the like. Thermosetting resins which char upon exposure to flame or intense heat are preferably used. Phenolic resins such as phenolformaldehyde copolymers and amineformaldehyde resins are used often. Flameresistant thermoplastic resins are also useful including halogenated polymers such as polyvinyl chloride, polyvinylidene chloride, ethylene-vinyl chloride copolymers and the like.

Impregnation is typically accomplished by immersing the dry paper into a resin bath and retaining it there until it has picked up the desired amount of resin. After impregnation, the sheets are typically dried or cured to a B-stage, assembled into a book with a decorative layer on top and laminated together in a press.

Typical laminates comprise 2 to 6 lamina of phenol-formaldehyde resin impregnated paper and one or a pair of decorative sheets and/or overlay sheets of paper impregnated or coated with an amine-formaldehyde resin. It has been found that the papers of the present invention can be printed with acceptable quality, resin impregnated and used as the decorative sheets in the laminate. Printing quality is improved substantially when the paper has been calendered.

Depending on the fire code specifications that must be satisfied, the decorative laminate may be formed entirely or in part form laminae of the paper of the present invention. To satisfy more stringent fire code standards, the decorative laminate can consist entirely of laminae of the paper of the present invention. On the other hand to satisfy less stringent standards, the laminate may consist of one or more laminae of the paper of the present invention and one or more Iaminae formed from resin impregnated kraft paper, e.g., kraft paper impregnated with phenolformaldehyde resin, or normal decorative paper saturated with an amine-formaldehyde resin.

The present invention is illustrated in more detail below by reference to the following nonlimiting examples.

EXAMPLE 1 A web was prepared by introducing 1 80 parts expanded #4 vermiculite, 645 parts Suzorite mica (200 mesh) (a product of Martin Marietta Corp.), 30 parts 0.25 inch DE chopped strand (Owens Corning Corp.), 90 parts refined northern softwood kraft fiber and 55 parts (solids) polyvinylidene chloride and 12,000 to 35,000 parts water to a beater chest to obtain a pulp having a consistency of about 3 to 8%. This stock was diluted to about 0.5 to 2.0% consistency and wet laid onto a Fourdrinier paper machine followed by wet processing and drying on steam heated drum dryers. The flame-resistant web so obtained was run through a resin treater where it was impregnated with phenol-formaldehyde resin and cured to a B-stage to provide a sheet of core stock in accordance with the present invention.

The core stock obtained was tested for its flame resistance by placing its bottom edge 1" above a Bunsen burner with a 2" flame for 15 seconds and found to exhibit self-extinguishing properties.

EXAMPLE 2 A web was prepared in a manner similar to Example 1 except the web consisted of 730 parts mica, 30 parts 0.25 inch DE chopped fiber glass, 40 parts (solids) polyvinylidene chloride, and 200 parts cellulose fiber. The web was impregnated with phenol-formaldehyde resin and tested for flame resistance as in Example 1. The sheet exhibited self-extinguishing properties.

While the product herein described constitutes a preferred embodiment of this invention, it is to be understood that the invention is not limited to this precise product, and that changes may be made therein without departing from the scope of the invention which is defined in the appended

Claims (26)

claims. CLAIMS

1. A paper comprising a flame-resistant web containing a non-combustible inorganic filler, said web being impregnated with resin, wherein said web is formed from a composition comprising 1 5 to 90% by weight of an inorganic filler, 5 to 30% of an organic fiber and 0 to 20% of a binder.

2. The paper of claim 1 wherein said inorganic filler is selected from mica, expanded vermiculite, unexpanded vermiculite, clay, wollastonite, talc, silicate, hydrated alumina and combinations thereof.

3. The paper of claim 2 wherein said inorganic filler consists of mica, vermiculite or a combination thereof.

4. The paper of claim 3 wherein said inorganic filler consists of mica.

5. The paper as claimed in any preceding claim wherein said binder is selected from polyvinyl chloride, polyvinylidene chloride, ethylene vinyl chloride copolymer, neoprene, and copolymers thereof.

6. The paper as claimed in any preceding claim wherein said web additionally comprises a noncombustible inorganic reinforcing fiber.

7. The paper of claim 6 wherein said noncombustible reinforcing fiber is glass fiber.

8. The paper of claim 6 wherein said web is formed from a composition which comprises mica, vermiculite or a combination thereof as said inorganic filler, a halogen-containing organic binder, cellulose fiber, and glass fiber.

9. The paper of claim 8 wherein said inorganic filler is present in an amount of 75 to 85 wt. %, said binder is present in an amount of 2 to 1 Q wt.

%, said cellulose fiber is present in an amount 9 to 20 wt. % and said glass fiber is present in an amount of O to 20 wt. %.

10. The paper as claimed in any preceding claim wherein said impregnating resin is phenolformaldehyde resin or an amine-formaldehyde resin.

11. The paper of claim 10 wherein said impregnating resin is a phenol-formaldehyde resin and the inorganic filler consists of mica.

12. A laminate comprising a plurality of laminae, at least one of said Iaminae being a paper comprising a flame-resistant web containing a non-combustible inorganic filler, said web being impregnated with a resin, wherein said web is formed from a composition comprising 15 to 90% by weight of an inorganic filler, 5 to 30% of an organic fiber and 0 to 20% of a binder.

13. The laminate of claim 12 wherein said inorganic filler is selected from mica, expanded vermiculite, unexpanded vermiculite, clay, wollastonite, talc, silicate, hydrated alumina and - combinations thereof.

14. The laminate of claim 13 wherein said inorganic filler consists of mica, vermiculite or a combination thereof.

1 5. The laminate of claim 14 wherein said inorganic filler consists of mica.

1 6. The laminate as claimed in any one of claims 11 to 1 5 wherein said binder is selected from polyvinyl chloride, polyvinylidene chloride, ethylene vinyl chloride copolymer, neoprene, and copolymers thereof.

1 7. The laminate as claimed in any one of claims 11 to 16 wherein said web additionally comprises a non-combustible reinforcing fiber.

18. The laminate of claim 17 wherein said noncombustible reinforcing fiber is glass fiber,

19. The laminate of claim 1 7 wherein said web is formed from a composition which comprises mica, vermiculite, or a combination thereof, a halogen-containing organic binder, cellulose fiber and glass fiber.

20. The laminate as claimed in any one of claims 12 to 19 wherein said impregnating resin is a phenolformaldehyde resin or an amineformaldehyde resin.

21. The laminate of claim 20 wherein said noncombustible inorganic filler consists of mica.

22. The laminate of claim 21 wherein said impregnating resin is a phenol-formaldehyde resin.

23. The laminate as claimed in any one of claims 1 2 to 22 wherein said lamina constitutes at least one face of said laminate.

24. The laminate as claimed in any one of claims 12 to 23 wherein said lamina is a decorative sheet.

25. A paper according to claim 1, substantially as herein described with reference to either of the Examples.

26. A paper according to claim 12, substantially as herein described.