Process for thermoforming reinforced polymer sheets

Claim 2

In a process for thermoforming a poly(ethylene terephthalate) sheet having a crystallinity of about 0-5% and a thickness of about 0.76-3.2 mm, which is reinforced with a mineral filler and, when so reinforced, has a tensile modulus at 100° C., defined as average of machine direction and transverse direction, within the range of about 7 to 70 MPa, as determinated according to ASTM D-638, preheated to a temperature of about 80°-130° C., at a draw ratio of less than about 1.8, defined as the ratio of the initial sheet thickness to the minimum wall thickness of the thermoformed article, and at a pressure differential of about 200-2000 kPa, in a mold having at least one surface adjacent said sheet of average roughness R A , of about 0.1-0.8 μm, the improvement, which produces a thermoformed article in which its essentially entire surface in contact with said mold surface has an R A of about 0.1 to 0.8 μm and the concave optical imperfection index of said surface is less than about 6% of the surface area, as determined by image analysis using a microscope having a magnification of 70 times, comprising the following steps: (A) removing air from the space between said mold surface and said thermoplastic sheet through at least one vent on the periphery of said mold surface to permit complete contact of said mold surface with said sheet, (B) while applying air pressure to the backside of said sheet, bringing said sheet, before poly(ethylene terephthalate) crystallinity exceeds about 15%, in complete contact with said mold surface maintained at a temperature of about 130°-180° C., to permit the sheet polymer to completely replicate said mold surface, (C) maintaining said sheet in contact with the mold at a temperature of 130°-180° C. at least until the sheet polymer reaches a degree of crystallinity sufficient to permit demolding without distortion, and (D) demolding the thermoformed article.

Claim 3

The improvement of claim 1 wherein the draw ratio is less than about 1.3.

Claim 4

The improvement of claim 1 wherein the pressure differential (in kilopascals) is at least equal to 200×(tensile modulus of PET sheet at 100° C., in megapascals)÷7.

Claim 5

The improvement of claim 1 wherein the mineral filler in glass fibers.

Claim 6

The improvement of claim 4 wherein the fiber average length to diameter ratio is at least 10.

Claim 7

The improvement of claim 1 wherein the amount of filler is about 5-50% based on the weight of the composition.

Claim 8

The improvement of claim 6 wherein the amount of filler is 10-35%.

Claim 9

The improvement of claim 1 wherein the PET sheet material also contains another polymeric material selected from the group consisting of dipolymers of ethylene with an unsaturated carboxylic acid, terpolymers of ethylene with an unsaturated carboxylic acid and an ester of an unsaturated carobyxlic acid, and terpolymers of ethylene with an unsaturated carboxylic acid and a vinyl ester, the proportion of the carboxylic acid in the dipolymers being about 2-20 weight percent, and the respective proportions of the carboxylic acid and of the ester in the terpolymers being about 1-30 weight percent of each; and the amount of the dipolymer or terpolymer being about 1-20% based on the weight of the reinforced polymer composition.

Claim 10

The improvement of claim 8 wherein the carboxylic groups are partly or completely neutralized with a divalent metal ion.

Claim 11

The improvement of claim 9 wherein the amount of the dipolymer or terpolymer is 3-10% based on the weight of the reinforced polymer composition.

Claim 12

The improvement of claim 1 wherein the mold temperature is about 140° C.

Claim 13

In a process for thermoforming in a mold a first sheet of poly(ethylene terephthalate) having a crystallinity of about 0-5% and a thickness of about 0.76-3.2 mm, which is reinforced with a mineral filler and, when so reinforced, has a tensile modulus at 100° C., determined as an average of machine direction and transverse direction, within the range of about 7 to 70 MPa, as determined according to ASTM D-638 preheated to a temperature of about 80°-130° C., at a draw ratio of less than about 1.8, defined as the ratio of the initial sheet thickness to the minimum wall thickness of the thermoformed article, the surface of the mold adjacent said sheet having an average roughness R A , of about 0.1-0.8 μm, and a second, reinforcing, poly(ethylene terephthalate) backing sheet and bonding the second sheet to the first while both sheets are in the mold, the improvement, which results in the first sheet having its essentially entire unbonded surface of an R A of about 0.1 to 0.8 μm, the concave optical imperfection index of said surface being less than about 6% of the surface area, as determined by image analysis using a microscope having a magnification of 70 times, said improvement comprising the following steps: (A) removing simultaneously or sequentially, beginning with the first sheet, air from the spaces between both sheets and their adjacent mold surfaces, maintained at a temperature of about 130°-180° C., through at least one vent on the periphery of each mold surface and holding prior to the introduction of air for about 1-4 seconds, (B) while applying air pressure between both sheets, forming both sheets into their desired shapes while the first sheet has a poly(ethylene terephthalate) crystallinity of at most about 15%, to permit the first sheet polymer to completely replicate the mold surface, (C) maintaining both sheets in contact with the hot mold surfaces at least until the polymer in each sheet polymer reaches a degree of crystallinity sufficient to permit bonding without distortion, and (D) bonding the second sheet to the first with an adhesive, while the first sheet is in contact with the mold, (E) maintaining the first sheet in contact with the mold until the bonded structure can be demolded without distortion, and (F) demolding the bonded article.

Claim 14

In a process for thermoforming in a mold a first sheet of poly(ethylene terephthalate) having a crystallinity of about 0-5% and a thickness of about 0.76-3.2 mm, which is reinforced with a mineral filler and, when so reinforced, has a tensile modulus at 100° C., determined as an average of machine direction and transverse direction, within the range of about 7 to 70 MPa, as determined according to ASTM D-638 preheated to a temperature of about 80°-130° C., at a draw ratio of less than about 1.8, defined as the ratio of the initial sheet thickness to the minimum wall thickness of the thermoformed article, the surface of the mold adjacent said sheet having an average roughness R A , of about 0.1-0.8 μm, and a second, reinforcing, poly(ethylene terephthalate) backing sheet and bonding the second sheet to the first while both sheets are in the mold, the improvement, which results in the first sheet having its essentially entire unbonded surface of an R A of about 0.1 to 0.8 μm, the concave optical imperfection index of said surface being less than about 6% of the surface area, as determined by image analysis using a microscope having a magnification of 70 times, said improvement comprising the following steps: (A) removing simultaneously or sequentially, beginning with the first sheet, air from the spaces between both sheets and their adjacent mold surfaces, maintained at a temperature of about 130°-180° C., through at least one vent on the periphery of each mold surface and holding prior to the introduction of air for about 1-4 seconds, (B) while applying air pressure between both sheets, forming both sheets into their desired shapes while the first sheet has a poly(ethylene terephthalate) crystallinity of at most about 15%, to permit the first sheet polymer to completely replicate the mold surface, (C) maintaining both sheets in contact with the hot mold surfaces at least until the polymer in each sheet polymer reaches a degree of crystallinity sufficient to permit bonding without distortion, and (D) bonding the second sheet to the first with an adhesive, while the first sheet is in contact with the mold, (E) maintaining the first sheet in contact with the mold until the bonded structure can be demolded without distortion, and (F) demolding the bonded article.

Claim 15

The improvement of claim 12 wherein the first sheet is thermoformed at a draw ratio of at most 1.3.

Claim 16

The improvement of claim 12 wherein the second sheet has the same composition as the first sheet.

Claim 17

The improvement of claim 12 wherein the mineral filler is glass fibers.

Claim 18

The improvement of claim 15 wherein the average length to diameter ratio is at least 10.

Claim 19

The improvement of claim 12 wherein the amount of filler is about 5-50% based on the weight of the composition.

Claim 20

The improvement of claim 17 wherein the amount of filler is 10-35%.

Claim 21

The improvement of claim 12 wherein the poly(ethylene terephthalate) sheet material also contains another polymeric material selected from the group consisting of dipolymers of ethylene with an unsaturated carboxylic acid, terpolymers of ethylene with an unsaturated carboxylic acid and an ester of an unsaturated carboxylic acid, and terpolymers of ethylene with an unsaturated carboxylic acid and a vinyl ester, the proportion of the carboxylic acid in the dipolymers being about 2-20 weight percent, and the respective proportions of the carboxylic acid and of the ester in the terpolymers being about 1-30 weight percent of each; and the amount of the dipolymer or terpolymer being about 1-20% based on the weight of the reinforced polymer composition.

Claim 22

The improvement of claim 19, wherein the carboxylic groups are partially or completely neutralized with zinc, magnesium, or calcium ions.

Claim 23

The improvement of claim 20 wherein the amount of the dipolymer or terpolymer is 3-10% based on the weight of the reinforced polymer composition.

Claim 24

The improvement of claim 12 wherein the mold temperature is about 140° C.