KR20010033739A - Low Haze, Speckle Free Polyester Film - Google Patents

Abstract

A low haze and spotless polyester film suitable for use in solar windows is disclosed. The film comprises a mixture of calcined silicon particles and fumed silica agglomerates. In essence, all fired silicon particles have a particle size of about 7 microns or less, and in essence, all fumed silica aggregates have a size of each micron or less. The film is very transparent and has a minimal blur.

Description

Low haze, spotless polyester film {Low Haze, Speckle Free Polyester Film}

Polymerizable linear polyester films have excellent stretch orientation and have been found to be particularly well suited for biaxial film orientation. These polymerizable films, in particular polyethylene terephthalate (PET) films, are strong and have excellent inherent chemical and thermal properties. In addition, these films have excellent optical transparency, toughness, and electrostatic properties, which makes them very suitable for use in countless applications.

Controlling surface slippage is a major requirement for commercial use of polyester films. Slip is important in processability of films, especially thin films. Slip is typically controlled by incorporating fillers to improve surface roughness. These additives include inert particles of materials such as silica, kaolin, aluminum silicate, calcium phosphate, and glass. By adding these fillers, the winding and slitting properties of the film are improved.

However, the film blurs and the transparency is lost by these additives, making the film unsuitable for certain installations, such as solar windows. Siddiqui, US Pat. No. 5,132,356, discloses a linear polyester film containing glass spheres and fumed silica aggregates. By adding these materials, the dynamic coefficient of friction and the static coefficient of the film are improved. Although the film is suitable for solar installations, there is a low haze, small amounts of spots, and optical distortion of light at the film surface.

Mills, Sidiqui, and Rakos, International Patent Publication No. WO 96/01739 (PCT / GB95 / 01589) disclose fired silicone resin particles and / or silicone resins in combination with clay particles on their surface. A polymerizable film composed of a polymerizable material layer having a polymerizable material layer containing particles is disclosed. Even if the optical and handling characteristics of the film are improved, the manufacturing cost is more expensive than that of the single layer film. In addition, the volume distribution median particle diameter of the particles is 1.5 to 12.5 microns. The presence of particles in excess of about 7 microns can result in spots.

Accordingly, there has been a continuing need for polyester films having good slip properties useful for solar installations and reduced cloudiness and spots.

<Summary of invention>

The present invention relates to an oriented thermosetting polyester film having good slip properties and reduced cloudiness and spots. The film comprises (a) about 2 ppm to about 20 ppm of calcined silicon particles (about 100% of the calcined silicon particles have a particle size of about 7 microns or less), and

(b) fumed silica agglomerates (about 100% of the agglomerates have an aggregate size of about 1 micron or less) based on the weight of the film.

The film has optical properties as well as good slip properties needed for solar window installations. Since the refractive index of the fumed silica agglomerates and calcined silicon particles is close to the refractive index of the biaxially oriented polyethylene terephthalate containing no additives, the film is very transparent and has a minimum blur.

The present invention relates to a polyester film. Specifically, the present invention relates to a polyester film containing calcined silicon particles and fumed silica particles, having a low haze and no speckle.

1 shows particle size distribution of Tospearl 130 silicone resin particles after firing at 300 ° C. for 45 minutes.

Fired silicon particles

The silicon particles comprise three-dimensional polymer chains of the formula:

R _x SiO _{2- (x / 2)}

Where

x is at least one positive number, preferably 1 to 1.9, more preferably 1 to 1.5, most preferably 1 to 1.2,

R is an aliphatic hydrocarbon group such as methyl, ethyl or butyl, or an aromatic hydrocarbon group such as phenyl, an unsaturated group such as vinyl or an organic group such as two or more of these groups.

R is preferably a hydrocarbon group having 1 to 8 carbon atoms, more preferably 1 to 5 carbon atoms. R is most preferably methyl. Particularly preferred silicone resin particles include methyl sesquioxanes. Silicone particles are described in detail in the above-mentioned International Patent Publication No. WO 96/01739.

The silicon particles have a crosslinked network of siloxane bonds, comprising a mixture of the following structural formulas:

RSi (O-) ₃ and (R) ₂ Si (O-) ₂

Wherein R is as defined above.

Suitable silicone particles are commercially available as silicone resin particles under the trade name "Tospearl" from Toshiba Silicone Co., Ltd., Tokyo, Japan. This particle has a three-dimensional network structure in which each silicon atom is bonded to one methyl group. Firing removes some or all of the groups or R groups, thereby reducing the x value. Once all organic groups are removed (ie x is zero), the particles are converted to silica (SiO ₂ ).

To form calcined silicon particles, the particles are calcined at about 300 ° C. to 400 ° C. for about 30 minutes to about 3 hours, preferably at about 300 ° C. for about 45 minutes. Firing may be carried out in air or in a suitable inert atmosphere such as nitrogen. Particle weight is reduced by removing some or all of the organic material during firing. The particles typically reduce from about 3% to about 5%, preferably from about 2% to about 4% of their initial weight when fired under these conditions.

The porosity of the calcined silicon particles enhances the adhesion of the particles to the polymer. Since the calcined silicon particles (mob hardness: 3) are soft compared to the glass particles (mob hardness: 6), there is less tendency to scratch the film during the winding and slitting process.

Fumed Silica Aggregates

Silicon tetrachloride (SiCl ₄ ) reacts in a hydrogen flame to form single spherical silicon dioxide droplets, which grow through coalescence and coalesce to form larger droplets. As the droplets continue to collide and cool and begin to freeze, the droplets are stuck together without coalescing to form a solid aggregate. Aggregates continue to collide to form clusters known as aggregates. The particle size of the fumed silica particles imparted by the manufacturer means the particle size of the cooled single spherical droplets rather than the size of the aggregates.

Furtherance

The film comprises calcined silicon particles about 2 to about 20 ppm, preferably about 4 to about 10 ppm by weight of the film.

The particle size of about 100% (ie, essentially all) of the calcined silicon particles is about 7 microns or less. Preferably, about 100% of the particles have a particle size of 6 microns or less, more preferably 5.5 microns or less. More preferably, about 100% of the calcined silicon particles have a particle size of about 6 microns or less, at least about 95% have a particle size of about 5 microns or less, and 50% have a particle size of about 2.2 microns or less. Calcined silicon particles typically have an average particle size of about 2 to about 3 microns, preferably about 2 to about 2.4 microns, more preferably about 2.2 microns. Because spots can occur due to the presence of particles in excess of about 7 microns, spots are reduced by removing larger particles. Of the glass particles disclosed in U.S. Patent No. 5,132,356 to Sidiqui, for example, about 3% of the glass particles have a particle size greater than about 7 microns.

About 100% (ie, essentially all) fumed silica aggregates are less than about 1 micron in size. The average aggregate size is preferably about 0.10 to about 0.50 microns, more preferably about 0.25 to 0.35 microns. Each fumed silica particle forming these aggregates generally has a particle size of about 0.05 micron. However, these particles are typically present as aggregates of two or more particles.

The concentration of the fumed silica agglomerates is suitable for imparting good winding properties to the film, but the optical properties of the film should be so high that they are not adversely affected by excessive clouding. The film comprises fumed silica agglomerates from about 20 ppm (0.002%) to about 6000 ppm (0.600%), preferably from about 500 ppm (0.005%) to about 3000 ppm (0.300%), more preferably by weight of the film. Comprises about 1000 ppm (0.100%) to about 2000 ppm (0.200%), even more preferably about 1400 ppm (0.140%) to about 1800 ppm (0.180%).

The polyester film preferably has a thickness of about 8 microns to about 75 microns, more preferably about 12 microns to about 15 microns.

Produce

Polyester films are known to those skilled in the art. Polymer preparation and film preparation processes are known to those skilled in the art and are described in Encylopedia of Polymer Science and Engineering, 2nd. Ed., Vol. 12, Wiley, New York, pp. 1-313, as well as many patent documents such as British Patent 838,708. Polyesters can be obtained by condensing one or more dicarboxylic acids or lower alkyl diesters thereof with one or more glycols. Preferred polyester films are films of the group consisting of polyethylene terephthalate (PET) films and polyethylene naphthanate films. These polymers are typically obtained by condensing a suitable dicarboxylic acid or lower alkyl diester thereof with ethylene glycol. Polyethylene terephthalate is formed from terephthalate acid and polyethylene naphthalate is formed from 2,7-naphthalene dicarboxylic acid. Most preferred polyester film is polyethylene terephthalate.

Calcined silicon particles and fumed silica agglomerates may be added to the polyester precursor at any point in the manufacturing process prior to polymer extrusion. Preference is given to adding during the polymerization step.

A particularly preferred easy procedure for the preparation of polyethylene terephthalate films is the addition of particles and aggregates to the polycondensation mixture used in the preparation of the polymer. Particular preference is given to adding the particles as a slurry after the transesterification reaction in which the monomers have been formed. Particles can be added, for example, as a slurry in the glycol from which the polyester is formed before the start of polycondensation. During polyethylene terephthalate preparation, the particles are added, for example, after the formation of bishydroxyethylene terephthalate (BHET). A conventional polyester polymerization catalyst is added and polymerization is carried out in a conventional manner to prepare a polyester resin.

To produce a polyester film, the polyester resin is melted and extruded as an amorphous sheet on a scrubbed rotating flexible film to form a cast sheet of polymer. The cast sheet of polymer is then heated to a temperature directly above its glass transition temperature for polyethylene terephthalate, 80 ° C. to 100 ° C., and generally elongated or stretched in one or more directions. The film is typically stretched in two directions, namely in the extrusion direction (longitudinal direction) and in a direction perpendicular to the extrusion direction (lateral direction) to form a biaxially oriented film. The first stretch that imparts stiffness and toughness to the film typically ranges from about 2.0 to 4.0 times the original length. In addition, subsequent stretching each increases the size of the film by about 2.0 to 4.0 times. In general, it is preferable to first stretch in the longitudinal direction and then in the transverse direction. The film is then thermally cured to polyethylene terephthalate at a temperature in the range of about 190 ° C. to 240 ° C. to fix stiffness, toughness and other physical properties.

The film may contain any additive known in the art, such as dyes, pigments, lubricants, antioxidants, tackifiers, surfactants, slip aids, gloss enhancers, ultraviolet stabilizers, viscosity control agents, dispersion stabilizers. However, in the case of polyethylene terephthalate in which the refractive index of the film is closely matched with the refractive indices of the fumed silica agglomerates and calcined silicon particles to prevent clouding, the additive should not have a significant effect on the refractive index of the film.

Conventional paints may be applied to the film. Such paints are commonly applied to improve the adhesion or antistatic properties of the film. The composition of these paints and the procedures for applying the paints are known to those skilled in the art and are described in a number of patent publications and publications, for example, US Pat. No. 5,132,356 to Sidiqui, incorporated herein by reference. The paint may be applied to a uniaxially or biaxially oriented film. In a simultaneous biaxially oriented stretching process, the paint may be applied before or after the stretching process. In the continuous stretching process, the paint is preferably applied between two processes, ie between the longitudinal and transverse stretching processes. Preferably, the film is stretched longitudinally on a series of rotating rollers, painted, stretched transversely in a stenter oven, preferably heat cured to obtain a painted film. The film can be metallized, for example, with gold or aluminum by techniques known in the art.

Glossary of Terms

Aerosil (R) OX-50: Amorphous fumed silica, particle size 0.050 micron each (Degussa, Ridgefield Park, NJ)

Tosprearl 130: silicone resin particles, average particle size 3.0 micron, specific surface area m ² , linseed oil absorption 75 mL / 100 g (manufactured by Toshiba Silicone Co., Ltd., Tokyo, Japan)

Preparation of Calcined Silicon Particles

Tospheric 130 silicone resin particles were baked in air at 300 ° C. for 45 minutes. The particles were analyzed by FTIR before and after firing. The steep peaks at 1288 cm ⁻¹ and 2991 cm ⁻¹ disappeared when the particles were calcined.

Particle size distribution was measured by a Microtrac particle size analyzer. The particle size distribution for the fired particles is shown in FIG. 1. All particles had a diameter of 5.28 microns or less, 99% of particles of 4.84 microns or less, 95% of particles of 4.07 microns or less, 90% of particles of 3.73 microns or less, and 50% of particles of 2.22 microns or less. Table 1 shows the analysis results.

Particle Size Distribution for Calcined Silicon Particles Particle Size (microns) Pass % 5.28 100.00 4.84 99.44 4.44 98.44 4.07 96.68 3.73 93.87 3.42 89.14 3.14 83.13 2.88 76.09 2.64 68.33 2.42 60.29 2.22 52.00 2.03 43.92 1.87 36.44 1.71 29.78 1.57 24.02 1.44 19.08 1.32 14.86 1.21 11.33 1.11 8.46 1.02 6.21 0.93 4.51 0.86 3.30 0.78 2.50 0.72 1.94 0.66 1.50 0.60 1.05 0.55 0.62 0.51 0.25 0.47 0.00

Example 1

This example illustrates the preparation of a filled biaxially oriented polyethylene terephthalate film containing calcined silicon particles and fumed silica aggregates.

Two kinds of slurries were prepared. The calcined tospheric 130 silicon particles prepared as described above were mixed with ethylene glycol to form a slurry with 1.0% calcined silicon particles in ethylene glycol. Aerosil® OX-50 amorphous fumed silica aggregate was mixed with ethylene glycol to form a slurry containing 4.0% fumed silica aggregate in ethylene glycol. Each slurry was mixed for 1 hour in a 5 gal Ross mixer under shear force.

To the melted bishydroxyethylene terephthalate (BHET) each slurry was added in an amount such that the desired final concentration of each additive was obtained. After the slurry was added, a conventional polymerization catalyst was added. The molten monomer was polymerized at a pressure of about 0.5 mmhg at 285 ° C to 290 ° C. The obtained polyethylene terephthalate (PET) resin was cooled and converted into chips.

The dried chips of PET resin were extruded into a film at 285 ° C. and then biaxially oriented by successively stretching them in a direction perpendicular to each other in a stretching direction of about 2.9: 1 in each direction. The film was thermally cured at 225 ° C. The thickness of the obtained film was 12 microns. The film contained 6 ppm of calcined silicon particles and 50 ppm (0.005%) of fumed silica aggregates.

The film had excellent optical and winding properties. Transparency was excellent. The haze measured by Gardner Hazemeter was 0.5%. Surface roughness measured on a 235 x 312 micron region of 20 magnification using a Wyko 3D interferometer was R _a = 10.4 nm; R _q = 12.3 nm; R _t = 704.3 mm. Using methods known in the art, the films described in the examples as well as other films can be metallized, for example with gold or aluminum, for use in solar installations.

Example 2

The procedure of Example 1 was repeated except that the film contained 6 ppm of calcined silicon particles and 1650 ppm (0.165%) of the fumed silica aggregate. The film had excellent optical and winding properties. Transparency was excellent. Cloudiness was 1.0%. Surface roughness is R _a = 20.6 nm; R _q = 27.6 nm; And R _t = 908.3 nm.

Example 3

The procedure of Example 1 was repeated except that the film contained 3 ppm of calcined silicon particles and 830 ppm (0.083%) of fumed silica aggregate. The film had excellent optical and winding properties. Transparency was excellent. Cloudiness was 0.8%. Surface roughness is R _a = 17.6 nm; R _q = 19.5 nm; And R _t = 807.7 nm.

Example 4

The procedure of Example 1 was repeated except that the film contained 6 ppm of calcined silicon particles and 1250 ppm (0.125%) of fumed silica agglomerates. The film had excellent optical and winding properties. Transparency was excellent. Cloudiness was 1.1%. Surface roughness is R _a = 19.7 nm; R _q = 22.3 nm; And R _t = 870.3 nm.

Example 5

The procedure of Example 1 was repeated except that the film contained 20 ppm of calcined silicon particles and 2200 ppm (0.22%) of fumed silica agglomerates. The film had excellent optical and winding properties. Transparency was excellent. Cloudiness was 1.4%. Surface roughness is R _a = 26.3 nm; R _q = 30.7 nm; And R _t = 1061.8 nm.

The inventors have described the present invention and now seek to claim the following claims and equivalents thereto.

The film can be used in solar window installations. In solar windows, the film can be metallized, dyed or painted to reduce light transmittance. In order to reduce ultraviolet transmittance and improve film aging properties, ultraviolet absorbers may be applied onto the film or incorporated into the polymers described above.

Hard paints, which may contain dyes and / or ultraviolet absorbers, may be applied to the outer surface of the film to improve surface scratch resistance. A pressure sensitive adhesive and a silicone-release release liner are applied to the opposite side used for application of the film to the glass. When using a metallized film, a laminate of two or more laminate layers of polyester film is used to protect the metallized side. The adhesive for the laminate may contain dyes and / or ultraviolet absorbers.

Advantageous properties of the invention can be observed with reference to the following examples which illustrate but do not limit the invention.

Claims (20)

(a) from about 2 ppm to about 20 ppm of calcined silicon particles (about 100% of the calcined silicon particles have a particle size of about 7 microns or less), and (b) fumed silica agglomerates (about 100% of the agglomerates have an aggregate size of about 1 micron or less) based on the weight of the film, comprising from about 20 ppm to about 6000 ppm, orienting and thermosetting Film which is a polyester film. The film of claim 1, wherein the polyester film is a polyethylene terephthalate film. The film of claim 2 comprising from about 500 ppm to 3000 ppm of fumed silica aggregates by weight of the film. The film of claim 2, wherein about 100% of the fired silicon particles have a particle size of about 6 microns or less. The film of claim 4 comprising from about 500 ppm to 3000 ppm of fumed silica agglomerates based on the weight of the film. 6. The film of claim 5 comprising about 4 ppm to 10 ppm of calcined silicon particles based on the weight of the film. The film of claim 6 comprising from about 500 ppm to 3000 ppm of fumed silica aggregates by weight of the film. The film of claim 7, wherein about 100% of the fired silicon particles have a particle size of about 5.5 microns or less. The film of claim 8, comprising from about 1400 ppm to 1800 ppm of fumed silica aggregate, based on the weight of the film. The method of claim 2, wherein about 100% of the fired silicon particles have a particle size of about 6 microns or less, at least about 95% of the fired silicon particles have a particle size of about 5 microns or less, and 50% have a particle size of about A film that is less than 2.2 microns. The film of claim 10 comprising from about 500 ppm to 3000 ppm of fumed silica aggregates by weight of the film. The film of claim 11, comprising about 4 ppm to 10 ppm calcined silicon particles based on the weight of the film. 13. The film of claim 12 comprising from about 1000 ppm to 2000 ppm of fumed silica aggregates by weight of the film. The film of claim 13, comprising from about 1400 ppm to 1800 ppm of fumed silica aggregate, based on the weight of the film. The film of claim 2, wherein the calcined silicon particles are prepared by calcining the silicone resin particles at about 300 ° C. to about 400 ° C. for about 30 minutes to about 3 hours. The calcined silicon particle of claim 15, wherein (a) about 100% of the calcined silicon particles have a particle size of about 6 microns or less, about 95% or more of the calcined silicon particles have a particle size of about 5 microns or less, and calcined silicon particles 50% of the particles have a particle size of about 2.2 microns or less, and (b) a film comprising from about 500 ppm to 3000 ppm of fumed silica aggregate by weight of the film. The film of claim 2, further comprising a metallized coating on the surface of the film. 18. The method of claim 17, wherein about 100% of the fired silicon particles have a particle size of about 6 microns or less, and at least about 95% of the fired silicon particles have a particle size of about 5 microns or less, and 50% of the fired silicon particles. Film having a particle size of about 2.2 microns or less. 19. The film of claim 18 comprising from about 1000 ppm to about 2000 ppm of fumed silica aggregates by weight of the film and from about 4 ppm to about 10 ppm of calcined silicon particles by weight of the film. The film of claim 18, wherein the metallized coating film comprises gold or aluminum.