Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a polyolefin plastic composition
; having improved transparency characteristics.
: Polyolefins, for example, polyethylene or polypropylene
have found a wide range of applications as packaging materials
and containers in the form of films, sheets, or hollow articles,
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but because of their poor transparency, their use has been limited
In particular, the~ are unsuitable as packaging materials or con-
tainers for such articles as are desired to be visible through the
(e.g., cosmetics or foodstuffs).
S Attempts have been made to improve the transparency of
polyolefins by incorporating certain kinds of additives in them.
For instance, para-t-butylbenzoic acid, its salts, low molecular
weight waxy polyethylene, and low molecular weight waxy poly-
propylene have heen suggested as such additives. These con-
ventional additives, however, are unable to bring about a
sufficient improvement of the transparency because they deteriorat
the mechanical and chemica:L properties of the products, or have
poor miscibility with the polyolefins~
More recently, as described in U. S. Patent Number
4,016,118 to Hamada et al., a polyolefin plastic composition
having improved transparency and reduced molding shrinkage
characteristics has been proposed which contains the compound di-
benzylidene sorbitol. While this additive has been shown to be
superior to those previously known for improving the transparenc~
characteristics of polyolefin plastic compositions, it would be
desirable to even further improve the transparency of such poly-
olefins without adversel~ affecting the mechanical and chemical
properties of the final products. Accordingly, the present in-
vention provides an additive which may improve the transparency
of polyolefins even as compared to the previously known product
dibenzylidene sorbitol which may not deteriorate the mechanical
and chemical properties of the final products.
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According to the present invention, a pol~olefin plastic
composition having improved transparency is provided which com-
prises a polymer selected from aliphatic polyolefins and co~
polymers containing at least one aliphatic ol~fin and one or more
ethylenically unsaturated comonomers and at least one di-acetal of
sorbitol, said di-acetal of sorbitol having the structure:
H
R R
Rl - ~ C H--C -O\ H ~ 3
R2 R I H/ C ~ ~ R4
H--C--OH
H--C--OH
H
wherein R, Rl, R2, R3 and R4 are selected from hydrogen, lower
alkyl, hydroxy, methoxy, mono- and di-alkylamino, amino, nitro and
halogen, with the proviso that at least one of Rl, R~, R3 and
R4 is chlorine or bromine.
It should be appreciated with regard to the structural
formula set forth above that while only the 1,3:2,4 isomer is
represented,this structure is provided for convenience only and th~
invention is not limited to only isomers of the 1,3:2,4 type, but
may include any and all other isomers as well so long as the com-
pound contains two aldehyde substituents on the sorbitol moiety.
The di-acetal of the present invention may be a con-
densation product of sorbitol and benzaldehyde or a substltu-ted
benzaldehyde. At least one o~ the benzaldehyde or substituted
benzaldehyde moieties is substituted in either or both o the meta
and para positions with a halo~en atom se:lected from chlorine and
bromine. Substituents which may be employed on -the substituted
.5
benzaldehyde moiety in any of the ortho, meta and para positions
include, for instance, in addition to chlorine and bromine, which
ust be provided in either or both of the meta and para positions
on at least one of the aldehyde substituents, lower alkyl, e.g.,
having from 1 to about 5 carbon atoms, hydroxy, methoxy, mono-
and di-alkvlamino, amino and halogen other than chlorine and
bromine. Preferred di-acetals of the present invention include
di-p-chlorobenzylidene sorbitol; di-m-chlorobenzvlidene sorbitol;
O-benzylidene-O-p-chlorobenzylidene sorbitol, di-m-bromobenzyli-
dene sorbitol, and bis(3,4-dichlorobenzvlidene) sorbitol.
The di-acetals of the present invention ma~ be conveniently
prepared by a variety of techniques, some of which are known in
the art. Generallyr such procedures employ the reaction of one
mole of D-sorbitol with about two moles of aldehyde in the
presence of an acid catalyst. The temperature employed in the
reaction will vary widely depending upon the characteristics, such
as melting poin~, of the aldehyde or aldehydes employed as a
starting material in the reaction. The reaction medium may be
an aqueous medium or a non-aqueous medium. One very advantageous
method which can be employed to prepare the di-acetals of the in-
vention is described in U. S. Patent No. 3,721,682, to Murai et al.
(New Japan Chemical Company Limited)~ While the disclosure of
the patent is limited to benzylidene sorbitols, it has been found
that the di~acetals of the present invention mav also be con-
veniently prepared by the method described therein.
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The di-acetals of sor~itol of the present invention pre-
- pared by the above techniques ma~ contain a minor or even a major
portion of by-product mono-acetal and tri-acetal as impurities.
Although it may not always ~e'necessary to remove these impurities
S prior to incorporation of the di-a~etal into the polyolefin, it
may be desira~le to do so and such ~rification may serve to
enhance the transparency of the resin produced thereby. Purifi-
cation o~ the di-acetal may ~e'acc~mpli9hed, for instance, by re-
moval of tri-ace~'al impurities by- the extraction thereof with a
relatively non-polar solvent. By removal of thè impurities, the
product may ~e purified so that ~he' amount of di-acetal in the
additive composition contains a~ least a~out 90 percent and even
up to about 95 percent di-acetal or more.
The proportion of di-acetal such as di-p chlorobenzylidene
sorbitol in the composition of this invention is an amount
sufficient to improve the'transp~rency of the composition,
generally from about O.Ol'to about 2 percent by weight, preferably
about .1 to about 1 percent ~ wei'ght, ~ased upon the total weight
of the composition may be'provided`. ~hen ~he content of di-acetal
is less than about 0.~01 percent ~y weight, the res'ulting com-
position may not be'sufficiently improved in respect to trans-
parency character'istics. W~en t~e 'a~ntent of di-acetal is
increased beyond about 2 per'cent by weight, no additional ad-
vantage can be observed.
The polyolefin polymers of the pre~en~ invention may include
aliphatic polyolefin~ and copolymers con~aining at least one
aliphatic ol in and one or more eth~lenically un~aturated
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i 161975
comonomers. Generally the comonomer if present will be provided
in a minor amount, e.g., about 10 percent or less or even about
5 percent or less, based upon the weight of the polyolefin. Such
comonomers may serve to assist in clarity improvement of the
polyolefin, or they may function to improve other properties of
the polymer. E~amples include acrylic acid and vinyl acetate, etc
Examples of olefin polymers whose transparency can be improved
conveniently according to the present invention are polymers and
copolymers of aliphatic monoolefins containing 2 to about 6 carbon
atoms which have an average molecular weight of from about 10,000
to about 500,000, preferably from about 30,000 to about 300,000,
such as polyethylene, polypropylene, crystalline e~hylene-
propylene copolymer, poly(l butene), and polymethylpentene. The
polyolefins of the present invention may be described as basically
linear, regular polymers which may optionally contain side chains
such as are found, for instance, in conventional, low density
polyethylene.
The olefin polymer or copolymer used in the composition of
the present invention is crystalline, and the diffraction of
light caused by micro crystals contained in it is considered to be
responsible for the deterioration of the transparency of the
polymer. It is thought that the di-acetal functions in the
composition to reduce the size of the microcrystals thereby im-
proving the transparency of the polymer.
The composition of the present invention can be obtained by
adding a specific amount of the di-ace~aJ. clirectly to the oleEin
polymer or copolymer, and merely mi~in~ them by any suitable
I 116191S
means. ~lternatively, a concentrate containing as much as about
10 percent by weight of the di-acetal in a polyolefin masterbatch
may be prepared and be subse~uently mixed with the resin.
Other additives such as a transparent coloring agent or
plasticizers (e.g., dioctyl phthalate, dibutyl phthalate, dioctyl
sebacate, or dioctyl adipate), can be added to the composition of
the present invention so long as they do not adversely affect the
improvement of transparency of the product. It has been found
that plasticizers such as those exemplified above mav in fact aid
in the improvement of the transparency by the di-acetal.
With regard to other additives it may also be desirable to
employ the di-acetals disclosed above in combination with other
conventional additives having known transparency improving effects
such as, for instance, para-~-butylbenzoic acid, its salts, low
molecular weight waxy poiypropylene and the lik~. It may even be
desirable to provide the particular di-acetals of the present in-
vention in the polyolefin composition in combination with the
previously described dibenzylidene sorbitol additive disclosed in
U. S. 4,016,118. In such applications, generally at least about
10 percent, preferably about 25 percent, or even abou~ 50 percent
or more of the clarity improving component will be the di-acetals
of the present invention, with the remainder being comprised of
other known clarifying agents~ plasticizers, etc.
The composition of the present invention is suitable as
a packing material and container material for cosmetics and food-
stuffs because it gives films, sheets or hollow articles
having improved transparenc~ characteristics and superior
mechanical and chemical properties.
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The fol~.owing examples further illustrate the present
invention. All parts a~d percents given in these examples are
by weight unless otherwise indicated.
EXAMPLE 1
Preparation of Di-p-chlorobenzylidene Sorbitol (I)
In a one liter round bottom flask equipped with overhead
stirrer, nitrogen gas inlet, Dean-Stark trap, and condenser wexe
placed 65.0 grams (0.25 mole) of 70 percent aqueous sorbitol,
70.3 grams (0.50 mole) of p-chlorobenzaldehyde, 15 milliliters of
dimethylsulfoxide, 2.0 milliliters of 70 percent methanesulfonic
acid, and 500 milliliters of cyclohexane. The mixture was stirred
vigorously under a nitrogen atmosphere and heated to reflux. When
the theoretical amount of water had distilled from the mixture
the reaction was halted. During the reflux period a thick, white
precipitate of the product formed. The precipitate was neutralized
with triethylamine, filtered, washed thoroughly with water, and
dried to give 66.2 grams of product as a white powder. The
product was purified by suspending it in dioxane (10 percent w/v)
and stirring the resulting mixture at 50C for 1 hour. The
mixture was filtered, and the solid obtained was washed with
additional dioxane and dried. The product had a meltiny point of
244-47C and was approximately 95 percent pure by high pressure
liquid chromatography.
EXAMPLE 2
Preparation of O-benz~l e_ - ~ )
O-benzylidene-O-p-chlorobenzylidene sorbitol (I~) was pre-
pared by the method of Example 1 usi.ng equimolar amounts o benzclld a_
hyde and p-chlorobenzaldehyde. It was isolated as a mixture with
11~1~75
dibenzylidene sorbitol (DBS) and di-p-chlorobenzylidene sorbitol
(DCBS) as shown by high pressure liquid chromatography. The
approximate ratio of DBS~ DC~S was 1:3,8:2. The mixture melted
at 207-214C.
EXAMPLE 3
Preparat:ion of ~ixture of Dibenz~lidene 50rbitol
and Di---p-chIoroben.ylVldene Sor~itol
A 50 percent mixture was prepared by mixing equal weights
of commercially available dibenzylidene sorbitol and di-p-chloro-
benzylidene sorbitol prepared by the method of Example 1.
EXAMPLES 4 AND 5
Di-m-tolylidene sorbitol [Example 4) and di-p-tolylidene
sorbitol (Example 5) disclosed in Japanese Patent No. SH0 53
~1978] - 117044 to Kobayashi et al., (New Japan Chemical Co., Ltd.)
were prepared from aqueous sorbitol and m-tolualdehyde and
p-tolualdehyde respectively according ko the method of Example 1.
The respective melting points were 216-219C and 2~7-248C.
EX~MPLE 6
Di-m-bromobenzylidene sorbitol was prepared from aqueous
sorbitol and m-bromobenzaldehyde according to the method of
Example 1. The product had a melting point of 247-250C.
EXAMPLE 7
Bis(3,4-dichlorobenzylidene)sorbitol was prepared from
aqueous sorbitol and 3,4-dichlorobenzaldehyde according to the
method of Example 1. The melting point of the product was 270C.
EXAMPLE 8
Di-o chlorobenzylidene sorbitol was prepared and purified
by the method of Example 1 yielding a white solid with a melting
point of 220-222C. Incorporation of this material into poly-
propylene at 0.5 percent gave a haze value of 50.
EXAMPLE 9
Di-p-methoxybenzylidene sorbitol was prepared and purified
by the method of ~xample 1 yielding a white solid with a melting
point of 185-187C. Incorporation of this material into poly-
propylene at 0.5 percent gave a haze value of 52.
EXAMPLE 10
Di-p-fluorobenzylidene sorbitol was prepared and purified by
the method of Example 1 yielding a white solid of melting point
214-218C. Incorporation of this material into polypropylene at
lS 0.25 percent gave a haze value of 17.
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EXAMPLE 11
Additives prepared pursuant to the preceding examples were
incorporated into polypropylene by first preparing a concentrate
containing the desired proportion of additive (either 3.75 grams
for a .25 percent concentration or 7.50 for a .5 percent concen-
tration) in 150 grams of a commercially available polypropylene
and mixing in a laboratory blender. Then additional amounts of
polypropylene powder (1350 grams) was added to the concentrate,
with stirring at approximately 700 rpm in a Welex mixer, until the
desired concentxation of additive wa~ achieved, e.g., either 0.25
percent or 0.5 percent as indicated in the ~able. The ~ixture was
. then extruded at 465F, pelletized and molded into thin p].aques o~
about 50 mils at 480F.
*Trademark.
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~ he haze and clarity values were measured by ASTM
Standard Test Method D1003-61 "Haze and luminous transmittance
of transparent Plastics."
TAB~E
EXAMPLE CONCEN-
S NO. ADDITIVE TRATION (~) HAZE (~) CLARITY (~)
none 72
dibenzylidene sorbitol 0.25 16 73
fo. 25 10 79
~0.38 9
1 di-p-chlorobenzylidene ~ 0.50 8
sorbitol ~0.75 9
~1.00 10
2 O-benzylidene-O-p-chloro-
benzylidene sorbitol 0.25 11 77
3 mixture of dibenzylidene
sorbitol and di-p-chloro-
benzylidene sorbitol 0.25 12
4 di-m-tolylidene
sorbitol 0.25 12 76
di-p-tolylidene
sorbitol 0.25 13 76
6 di-m-bromobenzylidene
sorbitol 0.50 11
7 bis(3,4-dichloro-
benzylidene) sorbitol 0.50 8
8 di-o-chlorobenzylidene
sorbitol 0.50 50
9 di-p-methoxybenzylidene
sorbitol 0.50 52
di-p-fluorobenzylidene
sorbitol 0.25 17
¦ 1161~5
~s the Table illustrates, compounds which are substituted
in either or both of the meta and para positions with either
chlorine or bromine atoms show a significant reduction in the haze
or increase in clarity in the polypropylene samples beyond that
provided by any prior clarifying agent including dibenzylidene
sorbitol which is presently av~ilable commercially, and even di-
m-tolylidene sorbitol and di-p-tolylidene sorbitol disclosed in th~
Japanese patent referred to above in Example 4, The mixed acetal
of Example 2, furthermore, shows an unexpected reduction in haze
over what would be anticipated from a compound containing one
benzylidene moie-ty and one p-chlorobenzylidene moiety. A priori
it would be expected that compound of Example 2 would show a haze
value intermediate between dibenzylidene sorbitol and di p-chloro~
benzylidene sorbitol. However, the compound shows a haze value
much closer to that of di p-chlorobenzylidene sorbitol. Likewise,
the mixture of Example 3 shows a reduction of haze out of pro-
portion to the concentration of the two components. Thus, at a
composition of 50 percent dibenzylidene sorbitol and 50 percent
di-p-chlorobenzylidene sorbitol the anticipated haze value would
be half way between that of the two pure components. Instead, the
mixture gives a reduc~ion greater than that expected.
