GB2113228A

GB2113228A - Foamable vinyl chloride resin compositions

Info

Publication number: GB2113228A
Application number: GB08300023A
Authority: GB
Inventors: David Morris Florence; Wayne Edward Smith
Original assignee: Armstrong World Industries Inc
Current assignee: Armstrong World Industries Inc
Priority date: 1982-01-04
Filing date: 1983-01-04
Publication date: 1983-08-03
Also published as: CA1206700A; DE3300040A1; ES8405827A1; AU1000883A; DE3300040C2; GB8300023D0; GB2113228B; AU561817B2; FR2519344A1; ES518755A0; FR2519344B1

Abstract

A blend suitable for preparing low density cellular products comprises (1) a vinyl chloride resin, e.g., polyvinyl chloride; (2) a rubber, e.g., butadiene- acrylonitrile; and (3) a polymerisable monomer, e.g., styrene. Insulation products such as sheets or tubes (for pipe insulation) are easily fabricated by freely expanding (i.e., without employing forming molds) blends of the invention which contain heat activated blowing agents.

Description

SPECIFICATION Low density cellular vinyl chloride resin The present invention relates to foamable and foamed vinyl chloride resins and, more particularly, is directed to foamable blends of a vinyl chloride resin and a rubber which are capable of being expanded to provide flexible, cellular products having a substantially ciosed-cell cellular system, and to cellular structures produced from the blends.

Cellular products such as sheets and tubes of expanded blends of vinyl chloride resins, and certain rubbers have achieved wide use as insulating materials, particularly for pipe insulation.

Expansible blends of polyvinyl chloride resin and certain rubbers that provide foamed products having a closed cell system are described in, for example, U.S. Patents Nos. 2,849,028 and 4,245,055.

In general, the aforementioned patents disclose a method of incorporating a blowing agent into a foamable resin/rubber blend which can be heated to decompose the blowing agent and thereby provide an expanded cellular object without the use of any forming molds. For instance, U.S. Patent No.

2,849,028 discloses blends of polyvinyl chloride resin and butadiene-acrylonitrile copolymer rubber that are freely expanded at a temperature of about 3000F (1 500C) to provide cellular products useful for pipe insulation. U.S. Patent No. 4,245,055 discloses similarly prepared cellular products prepared from a blend which includes polymethylmethacrylate.

According to the present invention there is provided a resin blend capable of being expanded to provide a cellular product, said blend comprising: (a) between 409/0 and 80% weight of a vinyl chloride resin, e.g., polyvinyl chloride; (b) between about 5% and about 40% of a rubber, e.g.

butadiene-acrylonitrile rubber; and, (c) a polymerizable, especially a polyfunctional, monomer.

Preferably, the monomer is selected from the group consisting of trimethylolpropane trimethacrylate, diallyl phthalate or styrene, and is present in an amount between 5% and 40% by weight, wherein all aforementioned weight percentages are based upon the total weight of components (a), (b) and (c).

According to the present invention there is further provided a cellular structure comprising between 40% and 80% by weight of a vinyl chloride resin; between 5% and 40% by weight of a rubber; and between 5% and 40% by weight of material derived from a pblymerizable, especially a polyfunctional monomer wherein said weight percentages are based upon the total weight of said resin rubber and monomer. The cellular product of the present invention may be either flexible or rigid and of either a closed cell or open cell cellular structure.

The vinyl chloride resin component of the blends of the present invention includes homopolymers such as, for example, polyvinyl chloride (PVC) and copolymers such as, for example, copolymers of vinyl chloride-vinyl acetate (VCVA). The PVC and VCVA resins are obtainable as standard articles of commerce which are readily available in the form of a white powder. Suitable PVC and VCVA resins useful for preparing foamable blends of the present invention include, for example, the following; GeonO 121 resin (B. F. Goodrich Company); FPC 4301 resin (Firestone Company).

The vinyl chloride resin component is present in the blends of the present invention in an amount between 40% and 80% by weight, preferably about 60% by weight. For instance, mixtures of PVC and VCVA may be used at the preferred quantity of 60% by weight with the ratio of VCVA:PVC advantageously being 3:1. The relative amounts of the VCVA and PVC components can be varied widely to achieve desired product properties. For example, increasing the amount of the VCVA copolymer provides cellular structures having lower softening temperatures which would be advantageous when thermoforming the cellular structures. On the other hand, higher amounts of the PVC homopolymer provide cellular products having higher softening temperatures.

The rubber component of the foamable blend of the present invention is advantageously a copolymer of butadiene such as, for example, a butadiene-styrene copolymer and a butadieneacrylonitrile copolymer.

Suitable butadiene rubbers for use in the blends of the present invention include, for example, the following: Paracril B acrylonitrile-butadiene copolymer (Uniroyal, Inc.); Hycar 1022 acrylonitrile copolymer (B. F. Goodrich Chemical Company).

The rubber component is present in the blends of the invention in an amount between about 5% and 40% by weight, preferably 25% by weight. Cellular products having greater flexibility and resilience are obtained when using higher quantities of the rubber component. Conversely, cellular products having greater rigidity are obtained when using lower quantities of the rubber component.

The polymerizable advantageously polyfunctional, monomer that constitutes an essential feature of the blends of the present invention includes monomers such as, for example, trimethylolpropane trimethylacrylate, styrene and diallyl phthalate. Suitable liquid monomers for use in the blends of the present invention include, for example, the following: SR-350 (Sartomer Resins, Inc.); DAP Monomer (FMC Corporation); and Styrene Mcnomer, SM (Monsanto Company).

The monomer is present in the blends of the invention in an amount between 5% and 40%, preferably 25% by weight. Greater ease of processability of the resin blend is obtained when using the higher quantity of the monomer.

A significant feature and advantage of the resin blend of the present invention is that the monomer component acts as a plasticizer which provides for greater ease of processability mentioned above. Also, the monomer component results in cellular products of very low density (e.g., cellular products having a density below one pound per cubic foot (16 kg/m3) have been obtained). Thus, the monomer enables the manufacture of cellular products that are both rigid and of low density.

If desired, any of the plasticizers normally used with resin or rubber systems may be incorporated into the blends of the present invention. The high-boiling esters, ethers, and ketones, for example, tricresyl phosphate, dibutyl phthalate, di-2-ethylhexyl phthalate, butyl phthalyl butyl glycolate, dibutyl sebacate, and the like are suitable. Generally speaking, the amount of plasticizer is not critical. The amount of plasticizer normally used to give good workable compositions will suffice in the present case. As is well known, too large an amount of plasticizer will yield a soft product having extremely fiexible cell walls. The amount of plasticizer will generally range between 5 and 60 parts by weight per 100 parts by weight rubber, preferably 30-50 parts by weight per 100 parts by weight rubber.

Incorporating additional plasticizers into the blends of the invention is not necessary when making rigid cellular products therefrom.

Lubricants such as stearic acid, including waxes such as paraffin or ceresin wax or wax mixtures, may be used in small amounts. Chlorinated paraffins which generally contain 38%70% chlorine can be used as a combination plasticizer and fire-retardant agent, particularly where antimony trioxide is used as part of the filler system. Other chlorinated plasticizers are suitable.

Various fillers may be incorporated into the blends of the invention in order to impart desired properties to the final product. Examples of such fillers are limestone, TiO2, slate flour, clay, silica, and carbon black. The total amount of filler will generally be about 5-1 50 parts by weight per 100 parts by weight rubber and, preferably, will be between 35-45 parts by weight per 100 parts by weight rubber. Mixtures of fillers may be used if desired. It is often convenient to incorporate antimony trioxide as part or all of the filler system in order to impart flame resistance to the final cellular product. The antimony trioxide is preferably used in an amount of about 10-20 parts by weight per 100 parts by weight rubber.Pigments may be incorporated in order to impart a desired color to the final product; products having different colors are useful in keying a piping system to aid in the identification of the substances carried by the individual pipe lines. Where a black product is needed, carbon black may be incorporated to strengthen the final product, as well as to impart a uniform dead black color to the final product.

The blowing agent to be used may, for example, be a nitrogen-producing, chemical blowing agent, to produce a closed cell structure. Many such blowing agents are known and commercially available; there may advantageously be used dinitroso pentamethylene tetramine, p,p'-oxybis (benzene sulfonyl hydrazide), benzene sulfonyl hydrazine, p-toluene sulfonyl semicarbazide and, preferably, azodicarbonamide.

The curing agent system may be any suitable to produce foamed products from resin/rubber blends. The nature of such systems is well known in the art. For instance, sulfur can be used to cure the rubber component of the resin blend of the invention. Also, conventional accelerator systems such as benzothiazole disulfide, zinc diethyl dithiocarbamate and diorthotolyl guanidine may be used.

Cross-linking agents such as, for example, a free radical generating agent, e.g., benzoyl peroxide, can be utilized to ensure substantially complete cross-linking of the polyfunctional monomer or incorporation of the polymerizable monomer. For instance, the benzoyl peroxide can be added to the resin blend at the same time that the sulfur curing agent is added.

The compounding of the resin/rubber blend of the present invention, as well as the compounding of the entire foamable system in which it is used, may proceed in conventional manner. Rubbers, resins, fillers, plasticizers, waxes, fire retardants, smoke suppressants, and any other conventional ingredients in these foams would normally be first blended on a mill or a Banbury in accordance with conventional procedures. The rubber may first be broken down, if desired, and any other cf these ingredients then added. When the portion of the final composition is suitably mixed, the curing agent system and the blowing agent may then be added.

An advantage of the resin/rubber blend of the present invention is that none of its components requires special handling beyond that normally used in the art of blending rubbers and resins to make foamable mixtures. At the same time, the resin/rubber blend of the present invention lends itself to compounding to achieve in the finished foam product any particular or special properties normally obtained in such products having a conventional higher density.

Once the completed composition has been prepared, it may be shaped as desired. To form pipe insulation, standard extruders may be used to extrude tubing in the desired sizes. Sheets may be formed by extruding, calendering, or molding. Specially shaped objects may be formed by molding.

Once the finished composition has been shaped into the desired form, it will be heated to a temperature sufficient to decompose the blowing agent and cure the system. The compositions of the invention expand linearly, as do the prior art systems, in that the finished, foamed dimensions consistently bear a constant relationship to the dimensions of the unfoamed composition. Temperature for expansion and cure will normally be in the range of about 2200--3600F (104-1 820C).

The principal advantage of the blends of the present invention is the ability to form unusually low density products in a reproducible manner. Cellular products having a density as low as 0.9 pounds per cubic foot (14.5 kg/m3) have been obtained.

The thermal conductivities of the low density cellular products of the invention are lower and thus represent an improvement in insulating properties when compared to high density cellular products.

The following examples illustrate the invention.

Example I-Ill The following formulations can be compounded by conventional procedures well known in the art.

The following ingredients can be placed on a mill or in a Banbury mixer and blended at a temperature below about 2500F (121 0C) during the conventional first process stage. The master batch product of Process Stage I is further processed in Stage II on a mill or in a Banbury mixer at a temperature below about 2000F (920C).

Example Example Example Ingredients I ll Ill Process Stage I Butadiene-acrylonitrile 25 25 25 PVC 25 25 25 VCVA 75 75 75 Trimethylol propane trimethacrylate 40 - Styrene monomer - 40 Diallyl phthalate - - 40 Polyethylene glycol 2.5 2.5 2.5 Calcium carbonate 5 5 5 Example Example Example Additional ingredients i II 111 Process Stage II Azodicarbonamide 31 31 31 Sulfur 2 2 2 Zinc oxide 2.5 2.5 2.5 Zinc dimethyl dithiocarbonate 0.5 0.5 0.5 Dipentamethylene thiuram hexa sulfide 0.5 0.5 0.5 The milled or mixed final batch of Stage II may be extruded in a conventional manner at a temperature between about 1250F (520C) and about 2250F (1070C). The shaped product is expanded by heating at a temperature of between about 2000 F (93 OC) and about 3600 F (1 820C) to provide the cellular products of the invention.

Claims

1. A resin blend capable of being expanded to provide a cellular product, said blend comprising between 40% and 80% by weight of a vinyl chloride resin; between 5% and 40% by weight of a rubber; and, a polymerizable monomer, the percentages by weight being based on the total weight of resin, rubber and monomer.

2. The resin blend of claim 1 wherein said vinyl chloride resin is polyvinyl chloride.

3. The resin blend of claim 1 wherein said vinyl chloride resin is a vinyl chloride-vinyl acetate copolymer.

4. The resin blend of claim 1 wherein said vinyl chloride resin is a mixture of polyvinyl chloride and a vinyl chloride-vinyl acetate copolymer.

5. The resin blend of claim 4 wherein the ratio of vinyl chloride-vinylacetate copolymer-to polyvinyl chloride is about 3:1.

6. The resin blend of any one of claims 1 to 5 wherein said rubber is a butadiene rubber.

7. The resin blend of claim 6 wherein said butadiene rubber is a butadiene-acrylonitrile copolymer.

8. The resin blend of any one of claims 1 to 7 wherein said monomer is present in an amount between 5% and 40% by weight.

9. The resin blend of any one of claims 1 to 8 wherein said polyfunctional monomer is trimethylolpropane trimethacrylate, styrene or diallyl phthalate.

10. The resin blend of any one of claims 1 to 9, which also comprises a blowing agent.

11. The resin blend of any one of claims 1 to 10, which also comprises a curing system for the rubber and a crosslinking agent.

12. The resin blend of claim 1, substantially as described in any one of the examples.

1 3. A cellular structure obtained from the resin blend of any one of claims 1 to 1 2.

14. A cellular structure comprising between 40% and 80% by weight of a vinyl chloride resin; between 5% and 40% by weight of a rubber; and between 5% and 40% by weight of material derived from a polymerizable monomer.

1 5. The cellular structure of claim 14 wherein said vinyl chloride resin is as specified in any one of claims 2 to 5.

16. The cellular structure of claim 14 or claim 1 5 wherein said rubber is as specified in claim 6 or claim 7.

17. The cellular structure of any one of claims 14 to 16 wherein said monomer is trimethylolpropane trimethacrylate, styrene or diallyl phthalate.

1 8. The cellular structure of claim 14, substantially as described in any one of the examples herein.

19. A shaped structure comprising a cellular structure as claimed in any one of claims 13 to 18.

20. Pipe insulation comprising a cellular structure as claimed in any one of claims 13 to 18.