Polyethylene terephthalate resin compositions containing filler or reinforcing agent, a selected sodium or potassium salt of a hydrocarbon acid or a salt of a selected organic polymer containing pendant carboxyl groups, and a selected low molecular weight organic ester, ketone, sulfone, sulfoxide, nitrile or amide. articles molded from the compositions have high gloss when molded at temperatures below 110° C.
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12. A molding composition which provides articles having smooth, glossy surfaces on release from a mold consisting essentially of
A. polyethylene terephthalate having an inherent viscosity of at least about 0.4; B. between about 10 and about 60 percent by weight reinforcing or filling material; C. a material selected from a sodium or potassium salt of a hydrocarbon acid containing between about 7 and 25 carbon atoms, or a sodium or potassium salt of an organic polymer which contains pendant carboxyl groups, said material present in an amount sufficient to provide a ΔHH /ΔHc ratio of less than 0.25 to a mixture of components A, B and C; D. A compound present in an amount sufficient to provide a tpk at least 4°C lower than the tkp of a mixture of components A, B and C, said compound being selected from (a) organic esters selected from the class consisting of (i) an ester of the product of benzoic acid and an alcohol of the formula (HOCH2 --2 R' wherein R' is alkylene of 4-6 carbon atoms or HO(R"O--y H wherein R" is ethylene or propylene and y is 2 or 3; (ii) tri-2-ethyl hexyl trimellitate; (iii) phenyl benzoate; (iv) trimethylolethane tribenzoate; (v) dioctylphthalate; (vi) diisodecylphthalate; (b) organic ketones of the formula ##STR5## (c) organic sulfones of the formula RSOOR, (d) organic sulfoxides of the formula R2 SO, (e) organic nitriles of the formula RCN, or (f) organic amides of the formula ##STR6## wherein the formulas (b) through (f) each R can be the same as, or different from, any other R and is a hydrocarbyl group of 1-25 carbon atoms, while in the formulas in (f) R' is hydrogen or a hydrocarbyl group of 1-25 carbon atoms. 1. A molding composition which provides articles having smooth, glossy surfaces on release from a mold consisting essentially of:
A. polyethylene terephthalate having an inherent viscosity of at least about 0.4; B. between about 10 and about 60 percent by weight reinforcing or filling material; C. a material selected from a sodium or potassium salt of a hydrocarbon acid containing between about 7 and 25 carbon atoms, or a sodium or potassium salt of an organic polymer which contains pendant carboxyl groups, said material present in an amount sufficient to provide a ΔHH /ΔHc ratio of less than 0.25 to a mixture of components A, B and C; D. a compound present in an amount sufficient to provide a tpk at least 4°C lower than the tpk of a mixture of components A, B and C, said compound being selected from (a) organic esters selected from the product of an aromatic carboxylic acid of 7-11 carbon atoms containing at least 1 carboxyl group per aromatic nucleus which is attached directly to said nucleus, and an alcohol selected from those of the formula (HOCH2 --x R' wherein x is 1, 2 or 3 and R' is a hydrocarbon radical of 2-15 carbon atoms or those of the formula HO--R"O)y '" wherein y is a cardinal number between 1 and 15, R" is a hydrocarbon radical of 2-15 carbon atoms, and R'" is --H or a hydrocarbon radical of 2-20 carbon atoms, (b) organic ketones of the formula ##STR3## (c) organic sulfones of the formula RSOOR, (d) organic sulfoxides of the formula R2 SO, (e) organic nitriles of the formula RCN, or (f) organic amides of the formula ##STR4## wherein in formulas (b) through (f) each R can be the same as, or different from, any other R and is a hydrocarbyl group of 1-25 carbon atoms, while in the formulas in (f) R' is hydrogen or a hydrocarbyl group of 1-25 carbon atoms.
13. A molding composition which provides articles having smooth, glossy surfaces on release from a mold consisting essentially of:
A. polyethylene terephthalate having an inherent viscosity of at least about 0.4; B. between about 10 and about 60 percent by weight reinforcing or filling material; C. at least one salt selected from the sodium and potassium salts of hydrocarbon carboxylic acids containing between about 7 and 25 carbon atoms, and the sodium and potassium salts of a carboxyl containing organic polymer, said salt present in an amount sufficient to provide a ΔHH /ΔHc ratio of less than 0.25 to a mixture of components A, B and C; D. at least one compound present in an amount sufficient to provide a tpk at least 4°C lower than the tpk of a mixture of components A, B and C, said compound being selected from (a) organic esters selected from the product of an aromatic carboxylic acid of 7-11 carbon atoms containing at least 1 carboxyl group per aromatic nucleus which is attached directly to said nucleus, and an alcohol selected from those of the formula (HOCH2)x R' wherein x is 1, 2 or 3 and R' is a hydrocarbon radical of 2-15 carbon atoms or those of the formula HO(R"O)y R"' wherein y is a cardinal number between 1 and 15, R" is a hydrocarbon radical of 2-15 carbon atoms, and R"' is --H or a hydrocarbon radical of 2-20 carbon atoms, (b) organic ketones of the formula ##STR7## (c) organic sulfones of the formula RSOOR, (d) organic sulfoxides of the formula R2 SO (e) organic nitriles of the formula RCN, (f) organic amides of the formula ##STR8## wherein in formulas (b) through (f) each R can be the same as, or different from, any other R and is a hydrocarbyl group of 1-25 carbon atoms, while in the formula in (f) R' is hydrogen or a hydrocarbyl group of 1-25 carbon atoms. 2. The composition of
3. The composition of
4. The composition of
5. The composition of
6. The composition of
7. The composition of
9. The composition of
10. An article having a smooth glossy surface molded from the composition of
11. A process for manufacturing a molded article having a smooth, glossy surface which comprises shaping a composition defined in
14. The composition of
15. The composition of
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This application is a continuation Ser. No. 496,938 filed May 23, 1983, now abandoned, which is a continuation-in-part of application of application Ser. No. 882,219, filed Feb. 28, 1978, now abandoned.
This invention relates to polyethylene terephthalate resins useful in molding applications. More particularly, this invention relates to polyethylene terephthalate resins containing an inorganic reinforcing or filler material.
It is desirable to enhance the strength of articles molded from polyethylene terephthalate resin by employing a reinforcing material such as glass fibers, asbestos fibers or other fibrous mineral materials with a coupling agent, in the resin. Furthermore, it is sometimes sufficient to merely increase the modulus by use of a filler, such as beads or a mineral of low aspect ratio, in the resin. However, heretofore, it was necessary to use very high mold temperatures, on the order of 130°C, to obtain molded articles from such reinforced or filled resins which had a glossy surface and which were not rough in texture. If these high mold temperatures were not employed, the molded articles had a rough surface with poor gloss. It is believed that the crystallization rate of polyethylene terephthalate is too slow below about 130°C to result in a molded article having good surface characteristics.
While good surface characteristics can be obtained at molding temperatures of 130°C or more, the use of such temperatures is not practical in the molding field, for most molds are heated with water and attain temperatures of only about 85°-110°C
A few molding devices employ heating means such as oil to reach temperatures higher than 85°-110°C but these generally are inconvenient to use and still either do not generally reach such temperatures or reach them unevenly because of inadequate coring. Because of these heating problems, it has proven commercially unattractive to employ these high temperature molding devices with reinforced or filled polyethylene terephthalate resins.
It is desirable to provide a reinforced or filled polyethylene terephthalate resin that can be molded at mold temperatures below about 110°C to produce a molded article having a smooth and glossy surface. The reinforced or filled polyethylene terephthalate resins of this invention achieve the foregoing by having incorporated therein (1) a sodium or potassium salt of a selected hydrocarbon acid or a sodium or potassium salt of a selected organic polymer containing pendant carboxyl groups and (2) a selected low molecular weight organic ester, ketone, sulfone, sulfoxide, nitrile or amide.
Specifically, the resins of this invention are compositions consisting essentially of:
A. polyethylene terephthalate having an intrinsic viscosity of at least about 0.4;
B. between about 10 and about 60 percent by weight reinforcing or filling material;
C. a material selected from a sodium or potassium salt of a hydrocarbon acid containing between about 7 and 25 carbon atoms, or a sodium or potassium salt of an organic polymer which contains pendant carboxyl groups, said material present in an amount sufficient to provide a ΔHH /ΔHc ratio of less than 0.25 to a mixture of components A, B and C;
D. a compound present in an amount sufficient to provide a Tpk at least 4°C lower than the Tpk of a mixture of components A, B and C, said compound being selected from
(a) organic esters selected from the product of an aromatic carboxylic acid of 7-11 carbon atoms containing at least 1 carboxyl group per aromatic nucleus, and an alcohol selected from those of the formula (HOCH2 --x R' wherein x is 1, 2 or 3 and R' is a hydrocarbon radical of 2-15 carbon atoms (preferably 2-10 carbon atoms) or those of the formula HO--R"O)y R'" wherein y is a cardinal number between 1 and 15 and preferably between 2 and 8, R" is a hydrocarbon radical of 2-15 carbon atoms (preferably 2-8 carbon atoms) and R'" is --H or a hydrocarbon radical of 2-20 carbon atoms (preferably 2-12 carbon atoms); or
(b) organic ketones of the formula ##STR1## (c) organic sulfones of the formula RSOOR (d) organic sulfoxides of the formula R2 SO
(e) organic nitriles of the formula RCN, or
(f) organic amides of the formula ##STR2## wherein in formulas (b) through (f) each R can be the same as or different from any other R and is a hydrocarbyl group of 1-25 carbon atoms, while in the formulas in (f) R' is hydrogen or a hydrocarbyl group of 1-25 carbon atoms.
The polyethylene terephthalate employed herein is one which has an inherent viscosity of at least 0.4 as measured by ASTM D-2857. The polyethylene terephthalate preferably has an upper limit on inherent viscosity of about 1.2. Inherent viscosity is measured in a 3:1 by volume ratio of methylene chloride and trifluoroacetic acid at 30°C The polyethylene terephthalate can contain minor amounts of other comonomers such as diethylene glycol or glutaric acid.
The reinforcing or filler material employed herein include glass fibers, glass beads, aluminum silicate, asbestos, mica and the like, or combinations thereof as for example a mixture of mica and glass fibers.
Materials present in an amount sufficient to cause the compositions of the invention to have a ΔHH /ΔHc ratio of less than 0.25 (component C defined above) include the sodium or potassium salts of hydrocarbon carboxylic acids containing between 7 and 25 carbon atoms, preferably more than 12 carbon atoms. Representative of these acids (which are fatty acids) are stearic, pelargonic, and behenic acid. These materials also include the sodium or potassium salts of carboxyl containing organic polymers, such as copolymers of olefins and acrylic or methacrylic acids, or copolymers of aromatic olefins and maleic anhydride. Preferably these materials include the sodium or potassium salt of stearic acid; the sodium or potassium salt of ethylene/methacrylic acid copolymers (including both wholly or partially neutralized salts e.g., at least about 30% neutralized), the sodium salt of styrene/maleic anhydride copolymers (including both wholly or partially neutralized salts e.g., at least about 30% neutralized) and sodium versatate. In the copolymers listed above the olefin or aromatic olefin moiety ordinarily comprises 50-98 percent by weight of the copolymer, and preferably 80-98 percent. An especially preferred material is the sodium salt of ethylene/methacrylic acid copolymer. The copolymers may be prepared by conventional high pressure polymerization technology.
Preferred organic esters of component D recited above are those in which the aromatic carboxylic acids are hydrocarbon acids containing 1-3 carboxyl groups and the alcohols are aliphatic. In other words, the R groups in the alcohols are alkyl or alkylene depending upon the particular R group. Preferably also when the carboxylic acids contain two or more carboxyl groups, the carboxyl groups are all reacted to form ester (COO) linkages, that is, there will be no free carboxyl groups present in the ester. Preferably, all the hydroxyl groups of the alcohols will also be reacted to form ester (COO) linkages, that is, there will be no free hydroxyl groups present in the ester.
A preferred class of esters are those in which the acid is benzoic acid, and the alcohol is (HOCH2)2 --R' wherein R' is alkylene of 4-6 carbon atoms (preferably neopentyl glycol) or HO(R"O)y H wherein R" is ethylene or propylene, and y is 2 or 3.
Preferred ketones, sulfones, sulfoxides, nitriles and amides are those in which the R groups in the formulas provided further above for these organic compounds are aryl groups of 6-10 carbon atoms or alkyl groups of 1-10 carbon atoms.
Specific compounds within these definitions are listed following (The number in parenthesis after each compound is the number of degrees centigrade that 1 percent by weight of the compound present (based on polyethylene terephthalate) in the reinforced or filled polyethylene terephthalate lower the Tpk): dibenzoate of neopentyl glycol (2.0), dibenzoate of triethylene glycol (3.0), dibenzoate of diethylene glycol (3.2), dibenzoate of dipropylene glycol (3.0), tris-2-ethyl hexyl trimellitate (2.5), phenyl benzoate (3.0), trimethylolethane tribenzoate (1.53), dioctylphthalate (1.3), diisodecyl phthalate (0.8), benzophenone (2.5), 4-fluorobenzophenone (1.9), diphenyl sulfone (2.8), N-ethyl-o,p-toluene sulfonamide (2.3), tolyl sulfoxide (2.6), lauryl nitrile (2.9), and erucyl nitrile (2.3).
Components (C) and (D) in the compositions of this invention aid in obtaining molded articles of high surface gloss at molding temperatures below 110°C by increasing the rate of crystallization of polyethylene terephthalate. Component (C) is believed to primarily aid in increasing the rate of crystallization while component (D) is believed to primarily improve the mobility of the polyethylene terephthalate in its supercooled state by reducing the viscosity in such state. Both are necessary to obtain the high gloss found in the articles molded from the composition.
The amount of component (C) present in the compositions of this invention is an amount which will result in a ΔHH /ΔHc ratio of the composition less than 0.25. To find the ΔHH /ΔHc ratio, polyethylene terephthalate is molded at 70° C. into 1/16" thick bars. The bars are heated and at between 95°C and 120°C an exotherm (termed ΔHH) is recorded on a differential scanning calormeter (DSC) cell attached to a Du Pont 900 Differential Thermal Analysis (DTA) device. The bar is heated to 290° (which is above its melting point) and the melted sample cooled at 10°C/minute. Another exotherm at between about 200°-220°C (termed ΔHc) is the exotherm recorded on freezing of the sample. It has been found that the ΔHH /ΔHc ratio is a convenient method of measuring the degree of crystallization.
The Tpk of the composition of this invention is the temperature at which heat evolves most rapidly during the heating cycle recited in the previous paragraph. As stated earlier the amount of component (D) present in the composition of this invention is an amount which lowers the Tpk of the composition by at least 4°C over that of an identical composition that does not contain component (D).
The upper limits on the amounts of components C and D are not critical. However, physical properties may become adversely affected as amounts increase. In general, the upper amount employed for any one component will usually be about 12 percent by weight based on weight polyethylene terephthalate, while the lower limit will be about 1 percent. For the preferred component (C) salts of ethylene/methacrylic acid copolymer the upper limit on the amount present will be about 12 percent by weight based on weight of polyethylene terephthalate while the lower limit will be about 0.5 percent, but preferably an amount within the range of 1-5 percent will be used.
In addition to the components discussed hereinabove, the compositions of this invention may contain additives commonly employed with polyester resins, such as colorants, mold release agents, antioxidants, ultraviolet light stabilizers, flame retardants and the like. Additives which improve physical properties, such as tensile strength and elongation can also be employed; such additives include epoxy compounds (e.g., an epoxy compound formed from bisphenol-A and epichlorohydrin) present in amounts of from 0.1-1.5 percent by weight based on weight of composition.
The compositions of this invention are prepared by blending the components together by any convenient means. Neither temperature nor pressure are critical. For example, the polyethylene terephthalate can be mixed dry in any suitable blender or tumbler with components B, C and D and the mixture melt-extruded. The extrudate can be chopped and mixed with reinforcing agent and then this mixture melt extruded. More conveniently, all the components can be mixed dry in any suitable blender or tumbler and the mixture then melt extruded.
The following Examples describe the best mode of carrying out the invention. The ΔHH /ΔHc ratio and the Tpk were determined as described above, while the gloss of molded sample was measured with a Gardner Multi Angle Gloss (Model GG-9095) set at a selected degree angle set forth in the Examples.
A dry blend of 92.57 percent by weight of dry polyethylene terephthalate having an inherent viscosity of about 0.5 to 0.6, 1 percent by weight sodium stearate, 5 percent by weight benzophenone, and 1.43 percent by weight N-stearyl erucamide (a mold release additive) was extruded through a 28 mm twin screw extruder at a melt temperature of approximately 264°C The chopped strands from the extruded melt were dried at about 110°C for 16 hours in a vacuum oven. The dried chopped strands were dry mixed with sufficient OCF 419AA glass fiber (chopped to 3/16") to make 30 percent glass fiber by weight and extruded through a 2-stage single screw extruder at about 264°C melt temperature. The ΔHH /ΔHc ratio was 0.06 and the Tpk was 12° less than the same composition but without the benzophenone present. The extruded strands were cooled and chopped and then dried at about 110°C for 16 hours in a vacuum oven. The dried chopped strands were molded in a 6 oz. injection molding machine at approximately 290°C with a fast ram, 20 seconds injection forward time, and 20 seconds mold close time and a 95°C cavity temperature. Gloss of the molded article was very good. As determined with a Gardner Multi Angle Gloss Meter (Model GG-9095) set at a twenty degree angle the gloss registered 23. At a 70° cavity temperature gloss measured in the same manner was 5.
In the Examples and comparisons which follow, the procedure generally employed to make compositions of this invention is as follows:
Dry polyethylene terephthalate having an inherent viscosity of about 0.5-0.65 was mixed manually with glass fiber as specified in the tables below and with ethylene/methacrylic acid copolymer (85/15 by weight) which had been 60 percent neutralized with sodium (which is component C herein) in an amount specified in the tables below and with the component D specified in the tables. Other additives may be present to improve strength of molded articles or to improve mold release properties. These additives, if present, are specified in the tables.
The resulting mixture was then extruded through a two-stage two inch single screw extruder at a melt temperature of 285°C and at a vacuum of 28 inches. The extruded strand was cut and the resulting resin pellets dried at 110°C in a vacuum oven for about 16 hours. The resin pellets were then molded into tumblers that were 9.2 cm high, 7.5 cm in diameter at the top, 5.5 cm in diameter at the bottom and which had a wall thickness of 0.19 cm. Melt temperature in the molding machine was 295°C; while the surface temperature of the mold was 85° C. Cycle times and release pressures are recited in the tables.
Gloss was measured at an angle of 60° by the Gardner Multi Angle Gloss Meter (Model GG-9095) several times for each sample. Gloss was measured around the circumference of the tumbler, at one-third the way down from the top. Pressure needed to release the tumbler was also measured by recording the air pressure necessary to move the ejector. The tables record the highest and the lowest gloss figures obtained in all the gloss tests performed on the sample. The tables also record the visual surface appearance of the molded tumblers.
In the tables, percent amount of components C and D are based on weight of polyethylene terephthalate employed. Percent amount of filler or reinforcing agent and other additives are based on weight of mixture that is to be extruded.
In the tables, component D is identified by a single letter. The letters represent the specific component D as follows:
A--Dibenzoate of neopentyl glycol
B--Lauryl nitrile
C--Dibenzoate of dipropylene glycol
D--Erucyl nitrile
E--Benzophenone
F--Trioctyl trimellitate
G--Diphenyl sulfone
H--N-ethyl-o,p-toluene sulfonamide
I--Dibenzoate of diethylene glycol
The reinforcing or filler material employed is identified in tables by two letters. The letters represent the specific materials as follows:
AA--OCF 277B glass fiber
BB--Mica (Suzorite A60) platelets
CC--OCF 419AA glass fiber
The other additives are identified by letter as follows:
X--epoxy formed from bisphenol A and epichlorohydrin
Y--tetrakis [methylene (3,5-di-tert-butyl-4-hydroxyhydroxycinnamate)] methane
| TABLE I |
| ______________________________________ |
| AMOUNT COM- OTHER |
| OF PONENT FILLER ADDI- |
| COM- D AND AND TIVES |
| PONENT AMOUNT AMOUNT PRESENT |
| EXAMPLE C (%) (%) (%) (%) |
| ______________________________________ |
| 2 5.8 A(5.7) AA(25) X(0.6) |
| Y(0.3) |
| 3 5.8 A(5.4) AA(35) X(0.55) |
| Y(0.25) |
| 4 5.9 A(5.4) AA(55) X(0.5) |
| Y(0.18) |
| 5 5.7 A(5.3) BB(30) NONE |
| 6 5.8 A(5.6) CC(25) NONE |
| 7 6.1 A(11.6) CC(25) NONE |
| 8 5.6 B(2.8) CC(25) NONE |
| 9 5.8 C(5.7) AA(25) X(0.6) |
| Y(0.3) |
| 10 5.8 D(4.3) CC(25) SAME |
| 11 2.1 E(5.1) CC(25) NONE |
| 12 5.7 F(3.7) CC(25) NONE |
| 13 5.8 G(5.3) CC(25) NONE |
| 14 5.8 H(5.3) CC(25) NONE |
| 15 5.7 I(3.7) CC(25) NONE |
| ______________________________________ |
| TABLE 2 |
| __________________________________________________________________________ |
| GLOSS AS |
| MOLDED (low- |
| RELEASE |
| est value/ |
| MOLDED |
| CYCLE |
| PRESSURE |
| highest SURFACE |
| Ex ΔHH /ΔHc |
| ΔTpk |
| TIME (psi) value) APPEARANCE |
| __________________________________________________________________________ |
| 2 0.16 -11 10/15 |
| 920 61/67 very smooth |
| 3 0.16 -10 10/10 |
| 940 52/60 very smooth |
| 4 0.16 -10 10/13 |
| 70 24/42 very smooth |
| 5 0.16 -10 10/30 |
| 370 27/32 very smooth |
| 6 0.16 -11 10/15 |
| 1060 62/69 very smooth |
| 7 0.16 -24 10/15 |
| 1080 58/62 smooth all |
| over |
| 8 0.16 -8.1 |
| 10/15 |
| 720 63/67 smooth all |
| over |
| 9 0.16 -17 10/10 |
| 970 55/65 very smooth |
| 10 0.16 -10 10/15 |
| 440 51/54 very smooth |
| 11 0.16 -13 10/15 |
| 1730 56/63 very smooth |
| 12 0.16 -9.3 |
| 10/15 |
| 1150 14/40 smooth |
| 13 0.16 -15 10/20 |
| 1230 24/58 very smooth |
| 14 0.16 -12 10/25 |
| 1290 20/40 smooth |
| 15 0.16 -12 10/15 |
| 1430 64/70 very smooth |
| all over |
| __________________________________________________________________________ |
In the following comparisons, the same general procedure was employed as was used in the preceding examples, and the tables which follow contain the same column headings as the tables above. Component C was varied in the comparisons and is listed for each comparison.
| TABLE 3 |
| __________________________________________________________________________ |
| COM- OTHER MOLDED |
| COM- |
| COM- PO- ADDI- RELEASE |
| GLOSS |
| SURFACE |
| PAR- |
| PONENT |
| NENT TIVES CYCLE PRESSURE |
| lowest/ |
| APPEAR- |
| ISON |
| C (%) D (%) |
| FILLER |
| (%) ΔHH /ΔHc |
| ΔTpk |
| TIME (psi) highest |
| ANCE |
| __________________________________________________________________________ |
| A NONE A(5.4) |
| AA(25) |
| X(0.6) |
| About Not 10/15 2150 29/38 |
| very rough |
| Y(0.3) |
| 0.4 Measured |
| Talc(0.7) |
| B Material |
| NONE CC(25) |
| N--stearyl |
| Not 0 10/30 1440 13/23 |
| moderately |
| Used in Erucamide |
| Measured rough |
| Examples Mold Re- surface |
| 2-15(5.5) lease |
| Agent(0.9) |
| C NONE E(10) |
| CC(25) |
| NONE About Not 10/30 had to 36/47 |
| rough |
| 0.5 Measured spray surface |
| mold |
| D Sodium |
| NONE CC(25) |
| Methyl |
| Not Not 10/25 1590 16/23 |
| very rough |
| Stearate Stearate |
| Measured |
| Measured surface |
| (0.5) (0.53) |
| E Material |
| A(1.4)* |
| CC(25) |
| NONE 0.16 -3 10/30 1790 9/18 |
| smooth to |
| Used in moderately |
| Examples rough |
| 2-15(5.5) |
| F Material |
| E(5.0) |
| CC(25) |
| NONE About Not Sticking/ |
| Spray 5/8 very rough |
| Used in 0.45 Measured |
| No molding |
| Examples cycle |
| 2-15(0.35) established |
| __________________________________________________________________________ |
| *Amount is too small |
Although gloss values for some of the experiments in Table 3 is in the range of gloss values found for some of the Examples in Table 2, the surface roughness is not acceptable in the experiments of the Comparisons.
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