Shaped articles from orientable polymers and polymer microbeads

We claim:

1. A shaped article selected from the group comprising films, sheets, bottles, tubes, fibers and rods wherein said article comprises a continuous oriented polymer phase selected from the group comprising polyesters and polypropylene having dispersed therein microbeads of a cross-linked polymer coated with a slop agent and which are at least partially bordered by void space, said microbeads being present in an amount of about 5-50% by weight based on the weight of said oriented polymer, said void space occupying about 2-60% by volume of said shaped article wherein said cross-linked polymer comprises polymerizable organic material which is a member selected from the group consisting of an alkenyl aromatic compound having the general formula ##STR4## wherein Ar represents an aromatic hydrocarbon radical, or an aromatic halohydracarbon radical of the benzene series and R is hydrogen or the methyl radical; acrylate-type monomers include monomers of the formula ##STR5## wherein R is selected from the group consisting of hydrogen and an alkyl radical containing from about 1 to 12 carbon atoms and R' is selected from he group consisting of hydrogen and methyl; copolymers of vinyl chloride and vinylidene chloride, acrylonitrile and vinyl chloride, vinyl bromide, vinyl esters having the formula ##STR6## wherein R is an alkyl radical containing from 2 to 18 carbon atoms; acrylic acid, methacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, oleic acid, vinylbenzoic acid; the synthetic polyester resins which are prepared by reacting terephthalic acid and dialkyl terephthalics or ester-forming derivatives thereof, with a glycol of the series HO(CH.sub.2).sub.n OH, wherein n is a whole number within the range of 2-10 and having reactive olefinic linkages within the polymer molecule, the hereinabove described polyesters which include copolymerized therein up to 20 percent by weight of a second acid or ester thereof having reactive olefinic unsaturation and mixtures thereof, and a cross-linking agent selected from the group consisting of divinylbenzene, diethylene glycol dimethacrylate, oiallyl fumarate, diallyl phthalate and mixtures thereof.

2. A shaped article according to claim 1, the composition of which when consisting only of said continuous phase and said microbeads at least partially bordered by void space is characterized by having a specific gravity of less than 1.20 and a Kubelka-Munk R value (infinite thickness) of about 0.90 to about 1.0 and the following Kubelka-Munk values when formed into a 3 mil thick film:

______________________________________ Opacity about 0.70 to about 1.0 SX 25 or less KX about 0.001 to 0.2 T (i) about 0.02 to 1.0 ______________________________________

3. A shaped article according to claim 1 wherein said oriented polymer phase is poly(ethylene terephthalate) having an I.V. of at least 0.50.

4. A shaped article according to claim 1 wherein said oriented polymer phase is a polyester having repeat units from terephthalic acid or naphthalene dicarboxylic acid and at least one glycol selected from the group consisting of ethylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol.

5. A shaped article according to claim 1 wherein said oriented polymer phase is polypropylene.

6. A shaped article according to claim 1 wherein said slip agent is selected from silica and alumina.

7. A shaped article according to claim 1 wherein said microbeads have an average diameter of about 0.1-50 microns.

8. A shaped article according to claim 1 wherein said void spaces surround said microbeads, said void spaces being oriented such that they lie in generally the same or parallel planes.

9. A shaped article according to claims 1, 2, 3, 4, 5, 6, 7 or 8 wherein said article is a fiber or rod of about 0.5-50 mils diameter.

10. A shaped article according to claims 1, 2, 3, 4, 5, 6, 7, or 8 wherein said article is a tube.

11. A shaped article according to claims 1, 2, 3, 4, 5, 7 or 8 wherein said article is a paper-like sheet.

12. A shaped article according to claim 1, 2, 3, 4, 5, 7 or 8 wherein said article is a bottle.

13. A paper-like sheet comprising a continuous phase of oriented polyester having dispersed therein microbeads of crosslinked polymer coated with a slip agent which are encircled by void space when viewed in a direction perpendicular to the plane of the sheet,

(a) said polyester having a Tg of about 60.degree.-100.degree. C. and an I.V. of at least 0.50,

(b) said crosslinked polymer comprises polymerizable organic material which is a member selected from the group consisting of an alkenyl aromatic compound having the general formula ##STR7## wherein Ar represents an aromatic hydrocarbon radical, or an aromatic halohydracarbon radical of the benzene series and R is hydrogen or the methyl radical; acrylate-type monomers include monomers of the formula ##STR8## wherein R is selected from the group consisting of hydrogen and an alkyl radical containing from about 1 to 12 carbon atoms and R' is selected from the group consisting of hydrogen and methyl; copolymers of vinyl chloride and vinylidene chloride, acrylonitrile and vinyl chloride, vinyl bromide, vinyl esters having the formula ##STR9## wherein R is an alkyl radical containing from 2 to 18 carbon atoms; acrylic acid, methacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, oleic acid, vinylbenzoic acid; the synthetic polyester resins which are prepared by reacting terephthalic acid and dialkyl terephthalics or ester-forming derivatives thereof, with a glycol of the series HO(CH.sub.2).sub.n OH, wherein n is a whole number within the range of 2-10 and having reactive olefinic linkages within the polymer molecule, the hereinabove described polyesters which include copolymerized therein up to 20 percent by weight of a second acid or ester thereof having reactive olefinic unsaturation and mixtures thereof, and a cross-linking agent selected from the group consisting of divinylbenzene, diethylene glycol dimethacrylate, oiallyl fumarate, diallyl phthalate and mixtures thereof,

(c) said microbeads having an average diameter of about 0.1-50 microns and being present in an amount of about 5-50% by weight based on the weight of said polyester, and

(d) said void space occupying about 2-60% by volume of said sheet.

14. A paper-like sheet according to claim 13 wherein said slip agent is selected from silica and alumina.

15. A fiber or rod comprising a continuous phase of oriented polyester having dispersed therein microbeads comprising crosslinked polymer coated with a slop agent bounded on the lengthwise sides by void space

(a) said oriented polyester having a Tg of about 60.degree.-100.degree. C. and an I.V. of at least 0.50,

(b) said microbeads having an average diameter of about 0.1-50 microns and accounting for 10-30% by weigh of said sheet, and

(c) said void space occupying about 2-60% by volume of said fiber or rod.

16. A fiber or rod according to claim 15 wherein said crosslinked polymer comprises polymerizable organic material which is a member selected from the group consisting of an alkenyl aromatic compound having the general formula ##STR10## wherein Ar represents an aromatic hydrocarbon radical, or an aromatic halohydracarbon radical of the benzene series and R is hydrogen or the methyl radical; acrylate-type monomers include monomers of the formula ##STR11## wherein R is selected from the group consisting of hydrogen and an alkyl radical containing from about 1 to 12 carbon atoms and R' is selected from the group consisting of hydrogen and methyl; copolymers of vinyl chloride and vinylidene chloride, acrylonitrile and vinyl chloride, vinyl bromide, vinyl esters having the formula ##STR12## wherein R is an alkyl radical containing from 2 to 18 carbon atoms; acrylic acid, methacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, oleic acid, vinylbenzoic acid; the synthetic polyester resins which are prepared by reacting terephthalic acid and dialkyl terephthalics or ester-forming derivatives thereof, with a glycol of the series HO(CH.sub.2).sub.n OH, wherein n is a whole number with the range of 2-10 and having reactive olefinic linkages within the polymer molecule, the hereinabove described polyesters which include copolymerized therein up to 20 percent by weight of a second acid or ester thereof having reactive olefinic unsaturation and mixtures thereof, and a cross-linking agent selected from the group consisting of divinylbenzene, diethylene glycol dimethacrylate, oiallyl fumarate, diallyl phthalate and mixtures thereof.

17. A fiber or rod according to claim 16 wherein said slip agent is selected from silica and alumina.

Description Submit all comments and votes

TECHNICAL FIELD

The present invention is directed to shaped articles such as films, sheets, bottles, tubes, fibers and rods having an oriented polymer continuous phase and polymer microbeads dispersed therein which are at least partially bordered by voids. The articles have unique properties of texture, opaqueness, whiteness in the absence of colorants, and generally good physical properties such as thermal stability, durability, and low density.

BACKGROUND OF THE INVENTION

Blends of linear polyesters with other incompatible materials of organic or inorganic nature to form microvoided structures are well-known in the art. U.S. Pat. No. 3,154,461 discloses, for example, linear polyesters blended with, for example, calcium carbonate. U.S. Pat. No. 3,944,699 discloses blends of linear polyesters with 3 to 27% of organic material such as ethylene or propylene polymer. U.S. Pat. No. 3,640,944 also discloses the use of poly(ethylene terephthalate) blended with 8% organic material such as polysulfone or poly(4-methyl-1-pentene). U.S. Pat. No. 4,377,616 discloses a blend of polypropylene to serve as the matrix with a small percentage of another and incompatible organic material, nylon, to initiate microvoiding in the polypropylene matrix. U.K. Patent Specification No. 1,563,591 discloses linear polyester polymers for making opaque thermoplastic film support in which have been blended finely divided particles of barium sulfate together with a void-promoting polyolefin, such as polyethylene, polypropylene or poly-4-methyl-1-pentene.

The above-mentioned patents show that it is known to use incompatible blends to form films having paper-like characteristics after such blends have been extruded into films and the films have been quenched, biaxially oriented and heat set. The minor component of the blend, due to its incompatibility with the major component of the blend, upon melt extrusion into film forms generally spherical particles each of which initiates a microvoid in the resulting matrix formed by the major component. The melting points of the void initiating particles, in the use of organic materials, should be above the glass transition temperature of the major component of the blend and particularly at the temperature of biaxial orientation.

As indicated in U.S. Pat. No. 4,377,616, spherical particles initiate voids of unusual regularity and orientation in a stratified relationship throughout the matrix material after biaxial orientation of the extruded film. Each void tends to be of like shape, not necessarily of like size since the size depends upon the size of the particle.

Ideally, each void assumes a shape defined by two opposed and edge contacting concave disks. In other words, the voids tend to have a lens-like or biconvex shape. The voids are oriented so that the two major dimensions are aligned in correspondence with the direction of orientation of the film structure. One major dimension is aligned with machine direction orientation, a second major dimension is aligned with the transverse direction orientation, and a minor dimension approximately corresponds to the cross-section dimension of the void-initiating particle.

The voids generally tend to be closed cells, and thus there is virtually no path open from one side of a biaxially oriented film to the other side through which liquid or gas can traverse. The term "void" is used herein to mean devoid of solid matter, although it is likely the "voids" contain a gas.

Upon biaxial orientation of the resulting extruded film, the film becomes white and opaque, the opacity resulting from light being scattered from the walls of the microvoids. The transmission of light through the film becomes lessened with increased number and with increased size of the microvoids relative to the size of a particle within each microvoid.

Also, upon biaxial orientation, a matte finish on the surface of the film results, as discussed in U.S. Pat. No. 3,154,461. The particles adjacent the surfaces of the film tend to be incompressible and thus form projections without rupturing the surface. Such matte finishes enable the film to be written upon with pencil or with inks, crayons, and the like.

U.S. Pat. No. 3,944,699 also indicates that the extrusion, quenching and stretching of the film may be effected by any process which is known in the art for producing oriented film, such as by a flat film process or a bubble or tubular process. The flat film process involves extruding the blend through a slit dye and rapidly quenching the extruded web upon a chilled casting drum so that the polyester component of the film is quenched into the amorphous state. The quenched film is then biaxially oriented by stretching in mutually perpendicular directions at a temperature above the glass transition temperature of the polyester. The film may be stretched in one direction and then in a second direction or may be simultaneously stretched in both directions. After the film has been stretched it is heat set by heating to a temperature sufficient to crystallize the polyester while restraining the film against retraction in both directions of stretching.

Paper is essentially a non-woven sheet of more or less randomly arrayed fibers. The key properties of these structures are opacity, texture, strength, and stability. Natural polymers are generally weaker and less stable. A serious problem, for example, is brightness reversion or fading of papers and fibers.

Although there are many ways to produce opaque media, this invention is concerned with creating opacity by stretching or orienting plastic materials to induce microvoids which scatter light, preferably white and ultraviolet light. A large body of prior art deals with this technique, wherein a plurality of inorganic solid particles are used as the dispersed phase, around which the microvoids form. Some significant problems associated with this approach are: (1) agglomeration and particle size control, (2) abrasive wear of extrusion equipment, guides, and cutters, (3) high specific gravity of these solids, (4) poor void nucleation around the solid particles due to the low thermal contraction of solids relative to liquids and polymer wetting and adhesion to the solid surfaces, (5) cost of these materials on a volume basis, and (6) handling and processing problems in general.

Of particular interest is U.S. Pat. No. 4,770,931 which is directed to articles comprising a continuous polyester phase having dispersed therein microbeads of cellulose acetate which are at least partially bordered by void space. The present invention is unexpected, however, in that while the geometries are similar, the cross-linked beads disclosed herein cavitate more efficiently generating higher void fractions and improved properties per weight of added beads. Also, the compositions of this invention have superior thermal and chemical stability, when compared with the prior art, especially the cellulose esters. Also, of particular interest is U.S. Pat. No. 4,320,207 which discloses oriented polyester film containing pulverized cross-linked polymers

DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view in section illustrating an embodiment of the present invention;

FIG. 2 is a perspective view in section illustrating another embodiment of the present invention;

FIG. 3 is a perspective view illustrating still another embodiment of the present invention;

FIG. 4 is a section of a shaped article in the form of a bottle;

FIG. 5 is an enlarged section view illustrating a cross-linked polymer microbead entrapped in a void in a polyester continuous matrix;

FIG. 6 is a sectional view taken along lines 6--6 of FIG. 5;

FIG. 7 is a sectional view similar to FIG. 5 illustrating a modification of the present invention; and

FIG. 8 is a graphical representation illustrating how the size of microvoids surrounding microbeads changes with respect to stretch ratio.

DESCRIPTION OF THE INVENTION

In accordance with the present invention, shaped articles are provided which have unique properties such as texture, opacity, low density, whiteness, etc. The articles are especially useful when in the form of film or sheet material (e.g., as a paper substitute) or when in the form of a biaxially oriented bottle (beverage container).

An important aspect of this invention is that during melt processing the orientable polymer does not react chemically or physically with the microbead polymer and/or its coating in such a way as to cause one or more of the following to occur to a significant or unacceptable degree: (a) alteration of the crystallization kinetics of the matrix polymer making it difficult to orient, (b) destruction of the matrix polymer, (c) destruction of the microbeads, (d) adhesion of the microbeads to the matrix polymer, or (e) generation of undesirable reaction products, such as toxic or high-color moieties.

Referring to the drawings, FIG. 1 illustrates a shaped article in the form of a sheet 10 which has been biaxially oriented [biaxially stretched, i.e., stretched in both the longitudinal (X) and transverse (Y) directions], as indicated by the arrows. The sheet 10 is illustrated in section, showing microbeads of polymer 12 contained within circular voids 14 in the polymer continuous matrix 16. The voids 14 surrounding the microbeads 12 are theoretically doughnut-shaped, but are often of irregular shape. Often, a line drawn perpendicular to and through the article will penetrate several voids and possibly some microbeads.

FIG. 2 also illustrates a shaped article in the form of a sheet 20 which has been unidirectionally oriented (stretched in one direction only, as indicated by the arrow). Microbeads of polymer 22 are contained between microvoids 24 and 24'. The microvoids in this instance form at opposite sides of the microbeads as the sheet is stretched. Thus, if the stretching is done in the machine direction (X) as indicated by the arrow, the voids will form on the leading and trailing sides of the microbeads. This is because of the unidirectional orientation as opposed to the bidirectional orientation of the sheet shown in FIG. 1. This is the only difference between FIG. 1 and 2. Note particularly the bumpy texture of the surfaces.

FIG. 3 illustrates a shaped article in the form of a fiber or rod 30 which has been oriented by stretching in the lengthwise (X) direction. The microbeads 32 of cross-linked polymer are bordered by microvoids 34 and 34'.

FIG. 4 illustrates a section of the wall of a shaped article 40 such as a bottle or wire coating. Due to the bidirectional orientation or stretching, the microvoids 42 are generally doughnut-shaped, surrounding the microbeads 44, in a manner similar to that shown in FIG. 1.

FIGS. 5 and 6 are sectional views illustrating enlargement of a section of a shaped article according to this invention, microbead 50 being entrapped within polymer continuous matrix 52 and encircled by void 54. These structures result from the shaped article being stretched in the X and Y directions.

FIG. 7 is a view similar to FIG. 5, except illustrating in enlarged form microbead 60 entrapped in polymer continuous matrix 62, having formed on opposite sides thereof microvoids 64 and 64', which are formed as the shaped article is stretched in the direction of the arrow X.

FIG. 8 is an enlargement illustrating the manner in which microvoids are formed in the polymer continuous matrix as th