Note: Descriptions are shown in the official language in which they were submitted.
3567
The invention is concerned with the production of
a flat sheet.
Upon exiting the extrusion die, a cellular vinyl
chloride or vinylidene chloride polymer extrudate expands
three dimensionally. The expansion in length direction is
picked up by a speed differential between the exiting
material and the puller. Expansion in the other two
directions, width and thickness, results in an increase in
width and thickness of the extruded profile. In cases where
the width is much greater than the thickness, such as in the
case of a sheet, the lateral expansion leads to the forma-
tion of folds in the machine direction. These folds are
undesirable for producing a flat sheet.
With certain cellular thermoplastics, these folds
are eliminated by mechanically stretching the extrudate to
take up the slack. In an existing process for making very
low density polystyrene foam sheet, such as is used for egg
carton stock, this is achieved by extruding through an
annular die opening and by stretching the tubular extrudate
over a conical mandrel prior to cutting and flattening the
sheet. This process is difficult to apply to thermo-
plastic materials such as rigid cellular vinyl in the 0.50
to 1.0 gram/cc. gravity range, because of the higher stiff-
ness of these materials. A meth~d for producing flat
cellular vinyl sheeting is desirable.
U.S. Patents 3,479,425, 3,398,431, 3,476,627 and
3,833,704 disclo~e coextrusion of thermoplastic materials.
In accordance with the invention there is provided
a method for producing flat vinyl chloride or vinylidene
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chloride polymer cellular sheet comprising coextruding a
heated polyolefin capstock with a heated vinyl chloride
or vinylidene chloride polymer sheet containing at least
one blowing agent, expanding said sheet into a cellular
sheet, and then cooling said cellular sheet and said poly-
olefin capstock below their softening temperature, to form
a product comprising said cellular sheet with said cap-
stock attached thereto, said capstock being incompatible
with said sheet and being readily strippable therefrom,
said capstock being effective during said expanding, to
restrict the expansion of the sheet in the width direction,
while allowing expansion in the height direction.
In another aspect of the invention there is pro-
vided a co-extruded combination comprising a polyolefin
capstock and a uinyl chloride or vinylidene chloride
polymer, cellul-ar sheet, said capstock being attached
to but incompatible with said sheet and being readily
~trippable from the sheet, said capstock being effective,
during expansion of said sheet to restrict the expansion
of the sheet in the width direction, while allowing
expansion in the height direction.
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~8567
Thus the invention provides flat sheets of vinyl
chloride or vinylidene chloride polymer cellular material
made by coextruding a cellular forming vinyl or vinylidene
chloride material, such as a rigid polyvinyl chloride
containing a chemical blowing agent, with a noncellular,
nonadhering polyolefin capstock. The polyolefin capstock
allows the blowing agent in the vinyl material to expand
the vinyl material in the height (thickness) direction
while restricting the expansion in the width direction.
After the vinyl chloride or vinylidene chloride polymer
material has expanded into a cellular sheet, the incom-
patible polyolefin capstock can be stripped
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off the cellular sheet giving a flat vi~yl chloride or
vinylidene chloride polymer cellular sheet. If desirable,
- the capstock may remain on the cellular sheet until after
the final product is produced such as by vacuum-forming and
then may be easily removed from the cellular sheet.
DETAILED DESCRIPTION
The flat cellular vinyl chloride or vinylidene
chloride polymer sheets of this invention are made by
incorporating a gas generating substance (blowing agent)
in the vinyl or vinylidene material~ The vinyl chloride
or vinylidene chloride polymer material containing the
blowing agent is then coextruded at a temperature above
their thermoplastic temperature with the noncellular non-
adhering capstock on one side of the vinyl material. Upon
exit from the extruder die, the vinyl or vinylidene material
is at a temperature sufficiently high to decompose the blow-
ing agent into a gaseous state thereby causing the viny~ or
vinylidene material to expand creating a cellular sheet.
The noncellular capstock restricts the expansion of the
cellular sheet in the width direction but allows expansion
in the height direction. The incompatible capstock can be
stripped off the cellular sheet after expansion and cooling
of the cellular sheet below its softening temperature or
even after the cellular sheet is converted into its final
product such as by vacuum forming. In some cases, it may be
desirable to leave the capstock on the cellular sheet as
a protective film until the product has been shipped to its
final destination and then remove the capstock.
Vinyl chloride and vinylidene chloride polymers used
in this invention include homopolymers, copolymers and blends
of homopolymers and/or copolymers. The vinyl chloride and
vinylidene chloride polymers may contain from 0 up to about
50~ by weight of at least one other olefinically unsaturated
monomer, more prçferably at least one other vinylidene
monomer (i.e., a monomer containing at least one terminal
CH2=C< group per molecule) copolymerized therewith, even
more prererably up to about 20~ by weight of such monomer.
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Suitable monomers include l-olefins containing from 2 to 12
carbon atoms, more preferably from 2 to 8 carbon atoms, such
as ethylene, propylene, l-butene, isobutylene, l-hexene,
4-methyl-1-pentene and the like; dienes containing from 4
to 10 carbon atoms including conjugated dienes as butadiene,
isoprene, piperylene, and the like; ethylidene norbornene
and dicyclopentadiene; vinyl esters and allyl esters such
as vinyl acetate, vinyl chloroacetate, vinyl propionate,
vinyl laurate, allyl acetate and the like; vinyl aromatics
such as styrene, -methylstyrene, chlorostyrene, vinyl
toluene, vinyl naphthalene and the like; ~inyl and allyl
ethers and ketones such as vinyl methyl ether, allyl methyl
ether, vinyl isobutyl ether, vinyl n-butyl ether, vinyl
. chloroethyl ether, methyl vinyl ketone and the like; vinyl
15 nitriles such as acrylonitrile, methacrylonitrile and the ..
like; cyanoalkyl acrylates such as ~-cyanomethyl acrylate,
the -, ~- and y- cyanoprcpyl acrylates and the like; ole-
finically unsaturated carboxylic acids and esters thereof,
including a,~-olefinically unsaturated acids and esters
thereof such as methyl acrylate, ethyl acrylate, chloropropyl
acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl
acrylate, dodecyl acrylate, octadecyl acrylate, cyclohexyl
acrylate, phenyl acrylate, glycidyl acrylate, methoxyethyl
acrylate, ethoxy-ethyl acrylate, hexylthio-ethyl acrylate,
methylmethacrylate, ethyl methacrylate, butyl methacrylate,
glycidyl methacrylate and the like, and including esters of
maleic and fumaric acid and the like; amides of the
olefinically unsaturated carboxylic aci.ds such as acrylamide
and the like; divinyls, diacrylates and other polyfunctional
monomers such as divinyl benzene divinyl ether, diethylene
glycol diacrylate, ethylene glycol dimethacrylate, methylene-
biR-acrylamide, al~yl pentaerythritol, and the like; and bis
(~-haloalkyl) alkenyl phosphonate such as bis (~-chloro-
ethyl) vinyl phosphonate and the like.
More preferred monomers include l-olefins contain-
; ing from 2 to 12 carbon atoms, more preferably from 2 to 8
` carbon atoms, such as ethylene, propylene, l-butene, iso-
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butylene, l-hexene, 4-methyl-1-pentene and the like; vinyl
esters and allyl esters such as vinyl acetate, vinyl chloro-
acetate, vinyl propionate, vinyl laurate, allyl acetate and
the like; ole~inically unsaturated carboxylic acids and
esters thereof, including a,~,-olefinically unsaturated acids
- - and esters thereof containing from 3 to 24 carbon atoms such
as methyl acrylate, ethyl acry~ate, chloropropyl acrylate,
; butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, dodecyl
acrylate, octadecyl acrylate, cyclohexyl acrylate, phenyl
acrylate, glycidyl acrylate, methoxyethyl acrylate, ethoxy-
ethyl acrylate, hexylthioacrylate, methyl methacrylate and
the like, and including esters of maleic and fumaric acid
and the like; and amides of a,~ olefinically unsaturated
carboxylic acids such as acrylamide and the like.
The vinyl chloride and vinylidene chloride polymers
may be prepared by any method known to the art such as by
emulsion, suspension, bulk or solution polymerization.
At least one blowing agent is mixed with the
polyvinyl chloride or polyvinylidene chloride material to
give a cellular product. The blowing agent is used in amounts
from about 0,1 to 3 weight parts per 100 weight parts of vinyl
material, preferably about 0.2 to less than 1.5. Cellular
polyvinyl chloride compositions having densities of about 0.7
to 0.8 have been obtained with 0.2 to 0.3 weight parts of
chemical blowing agent and cellular polyvinyl chloride com-
pos~,itions having densities of about 0.57 have been made with
i about 1.0 weight part of blowing agent. A variety of chemical
blowir.g agents are satisfactory in obtaining the cellular poly-
vi~y~1 chloride or polyvinylidene chloride sheets of this inven-
tion. The nitrogen releasing agents, for example, including
azobis-formamide, azobis-iso-butyronitrile, diazoaminobenzene,
p,p'-oxybis-(benzenesulfonylhydrazide), N,N'-dinitrosopenta-
~; methylenetetraamine, p,p'-azobis-(benzene-sulfonylsemicarbon-
amide), diethylazoisobutyrate, 1,3-bis-(xenyl) triazine,
4,4'-oxybis-(benzenesulfonylhydrazide) and the like have been
found to be useful. These generally are azo-, N-nitroso- and
~ sulfonyl hydrazide compounds.
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Catalysts based on lead, barium, cadmium, zinc
salts and the like may be used. These catalysts are activa-
tors and generally lower the temperatures of gas release of
the blowing agent. Excellent results have been obtained with
blowing agents releasing gas at temperature above 300F,
particularly above 350F.
~ ubricants ana lubricant mixtures may be included
in the compounds in amounts from about 1 to 5, preferably
2 to 4, weight parts including for example, paraffin, poly-
ethylene, calcium stearate, ethylenebis stearylamide a~dother lubricants known to and used by those skilled in the
art. High melting point lubricants, above 250F are pre-
ferred. Amide waxes and metal salts of fatty acids are of
this type.
Fine particle size inorganic fillers may also be
included in amounts from about 1 to 15 weight parts includ-
ing for example titanium dioxide, iron oxide, calcium carbon-
ate, silicas and the like.
Group IIA metal oxides and hydroxides particularly
calcium and magnesium oxide and hydroxide have been employed
in amounts from about 0.1 to 5 weight parts. Any of the
usual color pigments may be added to obtain desirable color
in the cellular sheets.
Stabilizers known to those skilled in the art as
the tin stabilizers, particularly the tin mercaptides, for
example, dibutyltinthioethyldiglycolate and the lauryl
derivative have been found useful in amounts from about
0.5 to 4 parts. Some synergism with the blowing agent has
been observed with these materials.
3Q The noncellular incompatible capstock is coextruded
with the cellular vinyl or vinylidene material. Materials
suitable for the incompatible capstock includes polyolefins
such as polyethylene, polypropylene, polyisobutylene and
the like. Polyethylene was found to be an excellent choice
as a capstock material. The thickness of the capstock will
normally be much less than the thickness of the cellular
sheet. The thickness of capstock used is tbat necessary to
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provide enough lateral resistance to prevent the cellular
material from expanding in the width direction. For example,
a cellular sheet having a thickness of about 0.1 inch requires
a capstock having a thickness of rrom about 0.001 to about
0.005 inch to restrict expansion in the lateral direction.
- The vinyl or vinylidene material and the polyolefin
capstock may be coextruded using any of the well known methods
of coextrusion. Coextrusion is a process whereby at least two
separate materials are extruded through a common die resulting
in a composite. A suitable method of coextrusion for use in
this invention is described in U.S. Patent 3 t 833,704
Other suitable methods of co-
extruding thermoplastics are described in U.S. Patents
3,476,627 and 3,479,425. During the extrusion process, the
materials are heated above their softening temperatures in
order to allow them to conform to the shape of the extrusion
die. The need for heating thermoplastic materials in order
to extrude them is well known in the art.
The cellular material together with the attached
capstock is cooled below their softening temperature before
the capstock is removed. For purposes of keeping the cellu-
lar material clean, it is preferred to not remove the capstock
until after shipment to its final destination. The capstock
can even be removed after the cellular material has been
shaped by vacuum forming into its final product or after
shipment of the product to its final destination.
; The cellular sheet of this invention will normally
have a density of from about 0.4 to about l.l grams per cubic
centimeter, preferably from about 0.5 to about 1.0 gram per
cubic centimeter.
The following example is presented to more fully
illustrate the present invention.
, EXAMPLE
; A rigid polyvinyl chloride resin having an inherent
viscosity of about 0.92; and containing one part by weight
of azobisformamide blowing agent per 100 parts by weight of
polyvinyl chloride, was coextruded in sheet form with a high
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density polyethylene (sp.gr. 0.95). The following extrusion
conditions were used:
Polyvinyl Chloride Material
Extruder: 2 1/2 inch Davis Standard Extruder 24:1
Screw: Mixing Screw, 0.185 inch Exit
Depth, Compression Ratio 2.7:1
Die: 15 inch Wide Flex Lip Die
Temperatu~e Zones-Barrel: 340F, 350F, 360F,
360F, 360F
10 Temperature Zones-Die: 355F, 360F, 355F
Head Pressure: 4000 PSI
Screw Speed: 15 RPM
Amperage: 30
Polyethylene Material
15 Extruder: 1 3/4 inch
Screw: Single Stage Mixing Screw -~
Die: Feed Block, Connected to 15 inch
Sheet Die
Temperature Zones: 330F, 330F, 330F, 350F -
20 Screw Speed: 2 RPM
Amperage: 5
- Using the above equipment and conditions, a 15 inch
wide flat cellular extrudate was obtained having a density of
0.57 g/cc. The cellular polyvinyl chloride layer was 75 mils
thick while the polyethylene layer was 2 mils thick. The ex-
trudate was cooled to a temperature below the thermoplastic
temperature of the polyvinyl chloride and the polyethylene.
After cooling, the polyethylene layer was easily removed
resulting in a flat cellular sheet of rigid polyvinyl chloride.
The flat cellular sheeting of this invention have
may uses, for example, they can be vacuum formed to produce
packaging containers or decorative articles.
