MXPA98000089A - Method for the thermoformation of poliolef resin - Google Patents

Abstract

A process is provided for the thermoforming of a polyolefin resin sheet having a condensation product of aromatic aldehyde-polyhydric alcohol incorporated in the sheet to limit the deformation of the sheet during the heating step.

Description

METHOD FOR THE TEPMOFOPMATION OF FOLIOLEFIN RESIN BACKGROUND OF THE INVENTION This invention relates to thermofor ac. Polyolefin resin resins, in particular to resins which incorporate a condensation product of aromatic-polyhydric aldehyde and an opacity pigment. The thermoforming of polyolefin resins includes the steps of heating a sheet of the resin until it softens, stretching the softened sheet against a solid mold and allowing the sheet to cool. The heating of the sheet is typically achieved by means of infrared radiation heaters or by means of forced convection hot air ovens. The ho is transported through the heating while suspended or fasteners mounted on bicycle-type chains that travel along the sides of the blade. Alternatively, the sheet can be suspended during transport by means of clothes-type fasteners. The polyolefin resins are semi-solid, that is to say, that upon cooling they form amorphous regions and crystalline regions. Because of the low mobility of the polymer chains and the high cooling rates that are typically used to process polyols, the polymer crystals are usually formed at various degrees of crystalline perfection. The crystalline regions act as a reticulated = > physical? > _ > _ > s that keep the pol or united. L? "=> Rel? U do = crystalline, in which the majority of polymers eucalyptus can flow elastically at temperatures above the glass transition temperature of the polymer. When the polymers are heated above the glass transition temperature, the distribution in crystalline perfection causes the polymer to melt in a range of several degrees. They have a limited thermal stability and are pri eros in melting.When the first less perfect crystals are melted, the physical reticles begin to melt and the love chain begins to relax and flow. , the polymer has pt> ages that are ideal for the thermos for this one solid structure but the polymer is easily deformed, with slightly higher temperatures , all the crystals melt, and the pol The number deforms like a viscous liquid. One of the difficulties encountered in the resin formation beroto is to maintain the temperature of the resin within the narrow processing window where the resin is sufficiently soft to be stretched and formed without losing the integrity of the troja. Frequently, under typical processing conditions, the resin sheet is buckled or warped when heated. The deformations in the sheet can in turn cause irregularities in the formed articles elaborated by the process, such as variations of height and thickness, expansion and thermal ani or r opp. The deformation observed in the heated oven and the resulting regularities can be exacerbated when using resins which have a relatively high melt flow index. Accordingly, reams having a melt flow index of 1 to 2 are typically employed. The aromatic aldehyde-alcohol polyolefin condensation products employed in the present invention have been incorporated in the refining, de poi or defoliants as agents of core formation to improve the clarity of the resin. It has been proposed that the producer of dense cores build up a number of nucleation sites in the ream when it is cooled.To the glass, the ream forms fine spherulites smaller than the wavelength of visible light. A description of the core forming agents can be found in Manpion US 5,310,950, and in the references mentioned herein.The use of the condensation product of aromatic aldehyde-polyhydric alcohol or gel-forming agents for organic solvents is described in the document US 4, 246,000 from Obayashi et al. The condensation products are dissolved in a mixture of liquid fuel and crude oil which is used to form a suspension of carbon in oil. The product of the condensation helps to avoid the settlement of the particles of? .rbó ?? finely »divided. The condensation products mentioned above have also been used with gel-forming agents in cosmetic pencils. For example, Ben fa to et al., US Pat. No. 5,376,363 discloses a composition containing ibenc i i idensorb i tol in a composition against transpiration. Adimically, the use of an idepsorb tol dibencí to improve the physical property of polyethylene, particularly to increase its resistance to stress and raise its melting point is presented in JP 45-22008 (1970) from Ha ada et al. A large part of the termo for ac. It is made with polyolefin resins that contain an opaque amount of pigment. Since the resin is intended to be opaque, there has been no motivation to incorporate the condensation products of aromatic aldehyde-polyhydric alcohol or other agent that improves the clarity of the resin. In addition, the potential benefits for the condensation products have not been recognized in terms of stability during the heating step and to facilitate the use of melt flow index resins at ta. SUMMARY OF THE INVENTION Accordingly, the objects of the present invention include: providing a method for the polyolefin resin thermosorbion with less variation in weight and thickness, less expansion and anisotropic shrinkage, and less overall shrinkage? provide a method with a greater range of operating temperatures for the heating step; providing - a method in which the beef leaf is heated while it is supported by its side edges; provide a process that has a minimum of sheet distortion or distortion; provide a process that can employ resins that have a relatively high melt flow index; and to provide a method for the thermaphor for opaque resins. By con «next», = > e provides a method having the steps of incorporating a condensation product of do mole of aromatic aldehyde and one mole of pentahydric alcohol or else there is an opaque amount of a pigment in the resin; form a resin in a ho; heating the ho a to a temperature above the softening temperature and below the melting temperature of the resin: forming the softened sheet in an article; and cool the formed article. In an alternative embodiment of the invention, a polyolefin resin having a melt flow index of 2.5 to 15, preferably 2.75 to 4.5, is used in the thermoforming process, and the incorporation of the condensation ptroduct mentioned. The resin may or may not be opaque. In addition to fulfilling the above objectives, the present invention has the features and advantages of extending the processing window of the heating step by several degrees centigrade and increasing the elasticity of the resin during the heating step, thereby increasing the integrity of the sheet . BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph of the storage module of polypropylene, both with and without acetal of bis (3,4-d imet i lbenci 1 iden) sorbitol, in a temperature range of 140 to 170"C. DETAILED DESCRIPTION OF THE INVENTION Without limiting the scope of the invention, preferred embodiments and characteristics are presented Unless otherwise indicated, all parts and percentages are indicated by weight and the conditions are under ambient conditions, i.e. an atmosphere and temperature of 25 ° C and the molecular weight is based on averages Unless otherwise specified, aliphatic hydrocarbons have a length of 1 to 12 carbon atoms, cycloalkyl hydrocarbons comprise from 3 to 8 carbon atoms and The aromatic compounds are single-ring and double-ring unsaturated hydrocarbons.All of the North American patents and other references cited in the specification are included. Orporan here by reference. The thermoforming process of polyolefin resin is a well-known process by experts in the field and is described in detail in Throne, "Ther oforming" (ISBN 3-446-14699-7) Hanser Publishers, Munich ( 1987). Briefly, the typical steps of the thermoforming process are fixation, heating, forming, elation, and trimming. The polyolefin resin is provided in sheets generally ca < • E gaged as "thin" (- "for ho less than 0.25 m)" thick "(sheet thickness greater than .25 mm) For most applications, ho a thicknesses are located Within a range of 0.25 mm to 12 m, preferably 0.5 mm to 2.5 mm, the sheet can be heated by infrared radiant heaters, forced convection hot air ovens, or a combination of convection and radiation heating Contact heating, where the ho is placed against a heated plate, is used in a special thermoforming area known as shaved hoa formation.The sheet is heated to a temperature above the softening temperature and below The melting temperature of the resin The softening temperature is characterized by the onset of melting in the amorphous stage, the melting temperature is characterized by the melting of substantially all the crystal regions. determined by means of a differential scanning calorimeter (DSC) or by means of a "buckling test" of the oven, observing when the blade starts to buckle in an uncontrollable way. The precise operating temperatures will depend on the individual resin used. Polypropylene polymers can be heated up to a temperature of 141 ° C to 164 ° C, preferably between 153 ° and 159 ° C. The ethylene content of the Vt of a random polypropylene copolymer (PCR) can be heated to a temperature from 125 ° C to 150 ° C, preferably from 133 ° C to 145 ° C, but the temperature will vary, significantly depending on the ethylene content. Once the sheet is heated to the desired temperature, it is formed into an article by molding. The basic mold configurations are the male mold, female mold and corresponding mold (matrix formation). The sheet can be pre-stretched before molding with air pressure or with a mechanical auxiliary known as mandrel. The sheet is held in the mold and cooled sufficiently so that the resin maintains its desired shape. The sheet can be cut out in the mold or in a separate cutting apparatus. Examples of polyolefin resins which may be employed in the thermoforming process of the present invention include oniferous aliphatic polymers and copolymers containing from 2 to 6 carbon atoms, which have an average molecular weight of about 10,000. about 2,000,000, preferably about 30, OOO to approve; 300,000, such as full poly tet, full low density pol l, polypropylene, crystalline (random or block), palm copolymer (1-butene) and polypropylene 13 Enten The polyols of the present invention can be described as regular, substantially linear, semi-circular polymers which may contain op- tonal side chains, as for example those found in conventional density poly- ethylene. Preferably, the polyolefin resin is a polypropylene homopolymer or random copolymer. The polyolefin resins of the present invention may include aliphatic polyolefins and copolymers made from at least one aliphatic olef and one or more latent unsaturated etiomeric comonomers. Generally, comonomers, if present, will be provided in a smaller amount, for example, about 10 * or less, or even about 5 * / ° or less, based on the weight of li? poliolef a. Such comonomers may serve to increase the mechanical and / or chemical properties of the polymer. Examples include acrylic acid, efcacric acid, and esters thereof, vinyl acetate, etc. The present invention can accept a variety of polyolefin resins. Therefore, those with a melt flow index of 0.6 to 15f from 0.6 MF to 15 MF) can be used, preferably from 1.8 MF to 4.5 MF. An advantage of the present invention is that while 2 MF MF t-resins are typically employed in the thermofurmation, resins having a melt flow index of 2.5 or greater, preferably from 2.75 to 4.5, can now be employed. to take advantage of the desirable performance ratios of these resins. A condensation product of two moles of an aromatic aldehyde and one mole of a palihydride alcohol, preferably a pentahydric or hexahydric alcohol such as, for example, "ilitol" or "sorbitol", respectively, is incorporated into the polyolefin resin before the resin form on a sheet. Examples of suitable aromatic aldehydes include benzaldehyde and naphthalened, which can be substituted with one or more substituents such as alkyl, halo, alkoKi, pol i < or Iquique), thioether. Substituents are also included where the alkyl group forms a carbonyl ring with the aromatic aldehyde. The condensation products of interest include sorbitan and xylital diacetals having the general formula: where p is 0 or 1, m and n are independently 0-3, P, in each case, is independently selected from C1-C8 alkyl, aleo: i C1-C4, idroxy, halogen, C1-C6 alkylthio, ali Isul faxi C1-C6, and urt alkyl group of 4 or 6 members forming a carbacyclic ring with adjacent carbon atoms of the iridescent ring of origin. The compounds wherein p is 1 P is selected from C 1 -C 3 alkyl, chlorine, bromine, thioether and a 4-membered alkyl group forming a cycloalkyl ring with adjacent carbon atoms of the unsaturated ring of origin are especially interesting. Examples of compounds that are useful herein include: di-benzyl-1-idensorbyl, d (p-et) Ibencid 1 idep) sorb i ol, di (o -me ilic 1 iden) sorbitol, i (p-et 13ben? 1 iden) so > ~ b i tol, i f dimet i lbencí 1? den) sorb? tol, specifically bi (2,4- dime i 3 bencí 1 iden) orb i tol and b? yes3,4- dimet i lben í 1? den > sorb i ol, bis (, 4- di t i lbenc 11 iden) sorbí tol, bi s (5 ', 6', "" ', 8' - tetrah ídr o-2 ~ nnf111? den) sorb? tol, bis (tp met i lbenc 11 iden) x i 11 tol and bi s í tr i et i Ibencí 1 ideri '' sorbí tol. Also within the scope of the present invention are compounds made with a mixture of aldehydes, including substituted and unsubstituted benzenediols, such as those presented in US Pat. No. 4,532,280 to i-Obayashi et al. ., in U.S. Patent No. 4,954,291 to f-obayashi et al. The diacetals of the present invention can be conveniently prepared by various known techniques. Generally, such processes employ the reaction of one mole of D-sorbitol or D-xylitol with approximately 2 moles of an aldehyde in the presence of an acid catalyst. The temperature used in the reaction varies greatly according to the characteristics, such as, for example, the melting point of the aldehyde (s) used as starting material in the reaction. Examples of suitable reaction medium are cyclohexane, or a combination of cyclohexane and methanol. The water produced by the condensation reaction is removed by distillation. Typically, the mixture is allowed to react for several hours, after which the reaction is cooled, neutralized, filtered, washed for example, with water or an alcohol, then stirred. Representative processes for the manufacture of the condensation products useful in the present invention are presented in the North American document 3,721,682 of Murai et al., And in EP 0 497 976 Al of ew Japan Company Ltd. The condensation product of aromatic aldehyde - polyhydric alcohol can be conveniently added directly to the polyolefin resin during the formation of compounds or provided as a resin concentrate, "recessed" by mixing with ream that does not contain the condensation product, prior to the formation of the resin in the resin. a leaf. The polyolefin resin resin can contain from 250 ppm to 2% "J, 0 <") 0 ppm of the condensation product, preferably between 500 ppm and 4, OO ppm. In addition to facilitating the use of relatively high melt flow rate polyalefin resin, the present invention includes the use of polyolefin resins that incorporate a condensation product of aromatic aldehyde-polyhydroxy alcohol and an opaque amount of pigment. Suitable pigments are presented in Gachter f. Muller, "Plastics Additives," third edition, (ISBN 3-446-1 680-1) Hanser Publishers, Munich (1990). Pigments typically have a range of primary particle sizes from 0.01 to 1 ml. Examples of suitable pigments include titanium dioxide, carbon black, carbon black, calcium carbonate, talc and organic pigments such as, for example, azo, phthalocyamine and anthraquinone pigments. The pigments are integrated into the resins by techniques well known to the experts in the materii, before the formation of the polyolefin resin in a ho a. The pigment is provided in a sufficient concentration to render the resin opaque, which can be characterized as having - less than 10 * /. of light transmission through a resin sheet. As examples, concentrations of 100 ppm to 40 * / can be used. by weight, preferably from 1,000 ppm to 2V "by weight of the pigment in the resin composition. The invention can be understood by way of reference with reference to the following examples which are not intended to limit the invention. EXAMPLE 1 The following example demonstrates that the incorporation of the condensation product of aromatic aldehyde-polyhydric alcohol in the resin increases the temperature range in which the softened resin hose maintains its elasticity during the thermoforming process. It is noted that the loss of elasticity results in wrinkling, creasing and buckling of the sheet during the heating step, which in turn causes irregularities and defects in the articles made from the sheet. RESINS Resin A-l: polypropylene homopalimera (2MF) Resin A-2: polypropylene hamopolymer (2MF) containing 1,900 ppm of bis (3,4-dimethylbenzene 1 iden) sorbitan acetal. Resin B-1: polypropylene homopolymer (4MF) Resin B-2: polypropylene homopolymer (4MF) containing 2,300 ppm of bis (3, 4-dimet i lberrci 1 iden) sorb i tol acetal. Resin C-1: polypropylene random copolymer (4MF), content of 3 * 4 of ethylene. Resin C-2: Polypropylene random copolymer (4MF), content of 3 ethylene, contains 2,300 parts per million of the b (3, 4-d ime i lbenc i 1 iden) sorbi tol acetal. Resin D-1: polypropylene random copolymer (2MF), content of 3% ethylene. Resin D-2: polypropylene random copolymer (12MF), content of 3 * /. of ethylene, contains 2,500 parts per million of the bis (3, 4-dimet i lbenci 1 iden) sorbitol acetal. All the resins tested had a package of commercial antioxidant, lubricant and acid-depleting additives. METHOD Viscoelastic measurements were made in oscillation mode using a CSL (2) 500 Dynamic Mechanical Rheometer from TA Instruments equipped with parallel plates of 4 cm diameter. Isof equency measurements were carried out either at 0.1 Hz or at 0.3 Hz while the sample was heated from 100 ° C to 170 ° C either at 2 ° C per minute or 5 ° C per minute. The voltage was adjusted to a nominal value of I V. The Dynamic Mechanical Rheometer was used to measure the viscosity properties of polypropylene while heating the sample from the solid phase to the liquid phase. In the course of the investigation, it was determined that the tandem modulus, G ', is the viscoelastic function most closely related to the polymer structure. The storage module, a measurement of the energy that is stored only during the deformation of a material v iscoelás ic, is analogous to a constant of elasticity. When the semi-solid polymer 3 i is not heated above the glass transition temperature, the storage modulus remains almost constant until the polymer starts to melt and the elasticity of the resin is substantially lost. During the fusion transition, the polymer structure melts and C decreases by several orders of magnitude. The temperature at which the elasticity is boiled is known as the "start" temperature. The results of the experiments are shown below in Table 1 and in the graph in Figure 1. TABLE 1 Acetal resin of temperature velocity bis _ Start (3, 4-di et i lbepci of start <l C) liden) sorbitol cooling of G '(ppm) CC / ntin) CC) A-l 0 5 157.9 A-2 1900 5 159.6 1.' B-l 0 5 158.9 B-2 2300 5 160.5 1.6 C-1 0 2 145.1 C-2 2300 2 - 147.2 2.1 D-l 0 2 143.4 D-2 2500 2 147.6 4.2 The results show that the starting temperature, measured as the temperature at which G 'em should deviate significantly from the value of G' in the plateau region, is increased by the incorporation of the condensation product of aromatic aldehyde - polyhydric alcohol in the resin. The temperature increase is within a range of 1.6ßC to 4.2 * 0. It is noted that the condensation products form a network of high aspect ratio fibers at the nanoscale which adds structures to the polymer melt by melting or thickening the amorphous regions. Due to the aggregate structure in the amorphous regions, the. Loss of elasticity occurs at a much lower velocity. Consequently, the formation of wrinkles, creases and buckling can be avoided more easily during thermofarming. EXAMPLE II The following example confirms the Theological data example I, using a Dynamic Mechanical Analyzer (DMA) to measure the tension or expansion of a polyolefin resin at its temperature with a very low load. In addition to testing the dr-'l resins Example I, a resin containing an opaque amount of titanium dioxide was also tested. RESIN Resin E-ls Polypropylene homopolymer (1.6 MF) containing 10,000 ppm of titanium dioxide. Resin E-2: polypropylene homopolymer (1.6 MF) containing 10,000 ppm of titanium dioxide and 1,900 ppm of bis (3,4-dimeti Ibenci 1 iden) sorbitol acetal. METHOD The force exerted on the polyolefin resin sheet, which is fixed along its sides, while it is heating during the thermoforming process was estimated between 0.5 and 2.5 Newtons. DMA was used in the dimensional recovery mode to model the load observed by the leaf in a thermoforming furnace. The sample was first heated to a temperature of 80 ° C, then fixed in the DMA jaws and the instrument was set to zero. The sample was slowly heated to an oscillating force, which ranged from 0.9 to 3 newton until the transition from the elastic state to the state of tensile flow was observed. The temperature at which the transition occurred was identified as the start temperature. The results appear below in Table 2. TABLE 2 Acetal resin of your T? 02 temperature Start (3,4-d? E ibenben- (ppm) of start <"C) liden) sorbitol CC) (ppm) A-l O - 148.79 A-2 1900 - 151.95 3.18 B-l 0 - 148.23 B-2 2300 - 150.48 2.25 C-1 0 - 133.43 C-2 2300 - 135.5 2.07 E-l 0 10000 148.35 E-2 1900 10000 151.73 3.38 The results confirm that the incorporation of the condensation product of aromatic aldehyde-polyhydric alcohol increases the starting temperature at which the elasticity of the resin is substantially reduced. This increase in the start temperature is very significant because it broadens the temperature region in which the polypropylene presents desirable elastic properties of an impor- 141 ° C to 148 ° C with the control homopolymer at about 141 ° C to 151 ° C with the homopolymer containing the sorbitol acetal. In addition to extending the processing window by approximately 40V, this innovation allows the processor to form parts at a higher temperature which allows the production of parts with less internal load. The . The difference in absolute values in terms of the starting temperature, between Example I and Example II, depends on the nature of the test apparatus and the geometry of the samples. EXAMPLE III (Comparison example) The following example demonstrates the application of sheet stabilization technology for the thermoforming process to control weight variations from part to part. The example also includes a comparison test of a commercial core forming agent for a polyolefin, which is outside the scope of the present invention. RESIN In addition to the Al and A-2 resins of Example I, a resin was prepared with the recommended charge of a commercial core forming agent based on phosphite available from Asahi De a Kogyo (Japan), sold under the trade name NA- 10 Resin A-3 is a polypropylene homopolymer (2r'F) containing 900 ppm of NA-10. METHOD bada resin formulation was extruded into a sheet and formed under pressure in containers with a capacity of 325c. The thermoforming equipment allowed the simultaneous molding of 8 containers. Then all the containers of one mole of particles were weighed and the standard deviation was calculated. The results appear below in Table 3. TABLE 3 Resin Additive Standard deviation (g) V * by weight Al - .134 1.92% A-2 1900 ppm acetal of bis .036 0.52% (3, 4-d imet i lbenc i 1 iden) sorbitol (ppm) A-3 900 ppm NA-10 .104 1.47X The results clearly demonstrate that there is less weight variation between part and part when the thermoforming process is carried out with a polyolefin resin having an aromatic aldehyde condensation product - incorporated polyhydric alcohol. In addition, the results were consistent with the observations made during the test according to which, after the heating step, the control sheets and the sheet containing NA-10 had a wavy, uneven appearance, while the sheet of the present invention It was flat before the training. EXAMPLE IV The following example demonstrates the application of sheet stabilization technology in the thermoforming process to produce parts that exhibit a less shrinking tendency when "filled with hot substance". RESIN Resin F-l: polypropylene homopolymer (4MF) Resin F-2: polypropylene homopolymer (4MF) with a content of 1,900 ppm of bis (3,4-dimethybenzyl 1 iden) sorbitan acetal. Resin G-1: polypropylene random copolymer (4MF) content of Z% ethylene. Resin 6-2: Random polypropylene copolymer (4MF) Z * A ethylene, containing 1,900 ppm of bis (3,4-dimethylbenzene 1 iden) sorbitan acetal. METHOD Each resin formulation was extruded in a sheet and formed under pressure in cups with a capacity of 200cc. 4 cups were selected for each resin sample and the outer diameter of the cup was accurately measured at a height of 1.27 cm above the base. Then, the cup was filled with 150 to 160 ml of water and heated in the microwave to the boiling point of the water for approximately one and a half minutes. The cups were cooled to room temperature for one hour. Finally, the external diameter of each cup was measured at a height of 1.27 cm above the base. The results appear below in Table 4 TABLE 4 Acetal resin of bis (3, 4- shrinkage dimeti lbenci 1 iden) average to one percent sorbitol (ppm) average height at one 1.27 cm (cm) height of 1.27 cm F-l O. 7112 F-: 1900 0.0 8 1.11 G-l 0.1524 1900 0.11 38: .5Y, The cups that were thermoformed from the resin containing the condensation product of aromatic aldehyde-polyhydric alcohol shrunk substantially less than the control cups. It is believed that the incorporation of the condensation products reduces the deformation in the sheet before the formation of the sheet in an article, which results in less stress in the formed article and less input when the article is filled with a fluid 1 Obviously there are many alternative embodiments and modifications to the present invention and such embodiments and modifications of ions are included within the scope of the following claims.

Claims (18)

1. CLAIMS 1. A process for the thermoforming of a polyolefin resin, comprising the steps of: (a) incorporating into resin (i) the condensation product of two moles of aromatic aldehyde and one mole of pentahydric or hexahydric alcohol; and (i i) a pigment in an amount sufficient for the resin to become opaque; (b) forming the resin in a sheet; (c) heating the resin sheet to a temperature above the softening temperature and below the melting temperature of the resin; (d) forming the softened sheet in an article; and (e) cooling the formed article.
2. 2. The process of claim 1, wherein the condensation product has the formula: where p is 0 or 1, m and n are, independently 0-3, R is selected, in each case, independently from C 1 -C 8 alkyl, C 1 -C 4 alkoxy, hydroxy, halogen, C 1 -C 6 alkylthio, C 1 -C 8 alkylsulfoxy C6, and a 4 or 6 membered alkyl group that forms a carbocyclic ring with adjacent carbon atoms of the ring of unsaturated origin.
3. 3. The process of claim 2 wherein the polyolefin resin is selected from the group consisting of homopolymer of polypropylene and random copolymer.
4. 4. The process of re-indication 2 where the pigment is selected from the group consisting of titanium dioxide, carbon black, calcium carbonate, talc and colored organic pigments.
5. 5. The process of claim 4 wherein the resin is homopolymer of the ipropylene and the sheet of resin is heated to a temperature between 153 ° C and 159'C.
6. 6. The process of rei indication 4 where the resin is a copal random number of polypropylene resin sheet is heated to a temperature between 1330C and 145 ° C.
7. 7. The process of the rei indicates ion 4 wherein the polyolefin resin is selected from the group consisting of polypropylene homopolymer and random copolymer.
8. 8. The process of claim 3 wherein the pigment is titanium dioxide and the pigment is incorporated into the resin in a concentration of 1,000 to 20,000 ppm.
9. 9. The process of claim 3 wherein the resin has a melt flow index of 2.5 to 15.
10. The process of claim 3 wherein the resin has a melt flow index of 2.75 to 4.5.
11. 11. A process for the thermoforming of a polyolefin resin, comprising the steps of: (a) incorporating into the resin the condensation product of two moles of an aromatic aldehyde and one mole of a pentahydric or hexahydric alcohol, where the resin has a melt flow rate from 2.5 to 15; (b) forming the resin in a sheet; (c) heating the resin sheet to a temperature above the softening temperature and below the melting temperature of the resin; (d) forming the softened sheet in an article; and (e) cooling the formed article.
12. 12. The process of rei indication 11 where the condensation product has the formula: where p is either 1-m and n are, independently 0-3, R is selected, in each case, independently, between C 1 -C 8 alkyl, C 1 -C 4 alkoxy, hydroxy, halogen, C 1 -C 6 alkylthio, C 1 -C 6 alkylsulfoxy, and a 4 or 6 membered alkyl group that forms a carbocyclic ring with adjacent carbon atoms of the ring of unsaturated origin.
13. 13. The process of claim 12 wherein the polyolefin resin is selected from the group consisting of polypropylene homopolymer and random copolymer.
14. 14. The process of claim 12 wherein the resin is a polypropylene homopolymer and the resin sheet is heated to a temperature between 153 ° C and 159 ° C.
15. 15. The process of claim 12 wherein the resin is a random copolymer of polypropylene and the resin sheet is heated to a temperature between 133 ° C and 145 ° C.
16. 16. The process of claim 13 wherein the polypropylene resin has a melt flow index of 2.75 to 4.5.
17. 17. The pyrolysis of the resin 16 where the resin is a polypropylene homopolymer and the resin sheet is heated to a temperature between 153 ° C and 159 ° C.
18. 18. The process of claim 16 wherein the resin is a random copolymer of polypropylene. and the resin sheet is heated to a temperature between 133 ° C and 145 ° C.