Abstract:
A fluorescent pigment includes a fluorescent dye and a resin carrier which is the polyamide reaction product of a diamine and a diacid. The fluorescent pigments are especially useful to color plastics and have improved resistance to plateout during molding. The pigments may be melt-blended with plastic to provide a color concentrate. The polyamide resins have a molecular weight in the range of 3,000 to 50,000 and may be readily ground to micron sized particles.

Description:
This is a continuation of application Ser. No. 409,099, filed Sept. 19, 1989 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION AND PRIOR ART 
     The present invention relates to fluorescent compositions including a fluorescent dye and a resin carrier, and, more particularly, to novel fluorescent compositions including an organic fluorescent dye and polyamide resin which are useful as colorants or pigments. 
     U.S. Pat. Nos. 2,938,873, 3,198,741, 3,412,036, 3,812,054 and 3,922,232 disclose various fluorescent compositions made from thermoplastic resinous materials which incorporate dyes for use as coating compositions and pigments. Of particular interest herein is the use of condensation resins as carriers for fluorescent dyes to provide fluorescent pigments useful as colorants for plastics. These materials have not been found to display the heat stability and other properties at temperatures and conditions required by certain polymer processing firms. 
     U.S. Pat. No. 3,915,884, which is assigned to the assignee of this application, teaches low molecular weight modified polyamides of improved heat stability. However, even these materials have not been entirely satisfactory. For example, the use of such pigments in blow molding techniques has been characterized by plateout or the tendency to deposit organic material such as oligomeric species on mold surfaces. Heretofore, modifications of the polyamides of the &#39;884 patent when used with specially selected additives were believed to have a lower degree of plateout in blow molding applications than other commercially available fluorescent pigment and were considered to set the standard in the industry. 
     In addition to heat stability and resistance to plateout, fluorescent pigments should be friable or grindable so that they may be reduced to relatively small particles for incorporation into plastics and other materials to be colored. For example, typical pigment particle size ranges were from 10 to 50 microns. As indicated by the patentee in the &#39;884 patent, the ability to provide particles of small size was previously thought to be hindered by increasing molecular weight of the resin carrier. Presumably, it is for this reason that the &#39;884 resin carriers are of relatively low molecular weight, e.g. less than 2,500. 
     The fluorescent dyes may be dissolved in the carrier resin to provide the pigment. Typical dye concentrations range up to about 15% based on the weight of the pigment. 
     For plastics processing, a masterbatch comprising pellets of a suitable plastic containing a relatively high concentration of pigment may be prepared by melt blending to provide a color concentrate for combination with the feed stock of plastics materials. The concentration of fluorescent composition or pigment in such prior art pellets has been limited usually to about 25 to 30% by weight due to the difficulty of forming uniform pellets which are free of fibrils at higher concentrations. The occurrence of fibrillation is believed to be associated with difficulties in solvating or dispersing the pigment at higher concentrations. It is desirable that relatively higher concentrations be achieved since this enables more efficient coloration. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, a thermoplastic polyamide resin which is a condensation product of a diamine and a diacid may be used as a carrier for fluorescent dyes to provide fluorescent compositions useful as pigments. Such fluorescent compositions have been found to provide pigments of adequate heat stability, improved resistance to plateout and which permit relatively high pigment concentrations to be achieved in the masterbatch. 
     The diamines used to produce the polyamide resin are of the general formula: 
     
         H.sub.2 N--R--NH.sub.2 
    
     wherein R is a straight or branched chain alkylene group of from 2 to 20 carbon atoms, or a cycloalkylene group of from 5 to 6 carbon atoms optionally having up to three ring substitutions which may be the same or different selected from the group consisting of C 1  -C 5  alkyl. Representative diamines include ethylenediamine, isophorone diamine, hexamethylenediamine, 1,12-dodecanediamine, 2-methylpentamethylenediamine, 2-ethyltetramethylenediamine, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, cis 1,4-diaminocyclohexane, and trans 1,4-diaminocyclohexane. 
     The diacid component used to produce the polyamide resins of the present invention comprises at least one dicarboxylic acid or its ester or anhydride derivative of the general formula: 
     
         R&#39;(COOH).sub.2 
    
     wherein R&#39; is a straight or branched chain alkylene group of from 3 to 20 carbon atoms, a cycloalkylene group of from 5 to 6 carbon atoms optionally having up to three ring substitutions which may be the same or different selected from the group consisting of C 1  -C 5  alkyl, or a monocyclic or bicyclic arylene group of from 6 to 10 carbon atoms optionally having up to six ring substitutions which may be the same or different selected from the group consisting of C 1  -C 5  alkyl or a C 1  -C 2  dialkyl ester or an anhydride of the diacid formed by said monocyclic or bicyclic arylene group. 
     Representative dicarboxylic acids or ester or anhydride derivatives include phthalic acid/phthalic anhydride, isophthalic acid, terephthalic acid, 2,6-naphthalene dicarboxylic acid, succinic acid/succinic anhydride, glutaric acid, adipic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, mixtures of succinic, glutaric and adipic acids, cyclohexane dicarboxylic acid, dimethyl isophthalate, dimethyl phthalate, dimethyl terephthalate, dimethyl 2,6-naphthalene dicarboxylate, diethyl oxalate, dimethyl adipate, dimethyl glutarate and dimethyl succinate. 
     Preferred polyamides are prepared from the branched aliphatic diamines having 4 to 16 carbon atoms and phthalic acid, isophthalic acid, terephthalic acid or adipic acid. 
     In the preparation of polyamide resins in accordance with the invention, a stoichiometric excess of the diacid component is used in the condensation reaction. The resins are prepared by reacting about 0.5 to about 1.5 moles of diacid per mole of diamine, and; more preferably, 1.0 to 1.25 moles of diacid per mole of diamine. The polyamide resins are substantially linear and have a weight-average molecular weight in the range of from about 3,000 to about 50,000, and, more preferably, from about 4,000 to about 15,000. Reaction terminators are not required. Molecular weight may be controlled by regulation of the reaction time. 
     The fluorescent dyes employed in the compositions include fluorescent organics which are brilliantly fluorescent when in solution in vehicles such as resins and gums. These daylight fluorescent-type dyes are well known in the art and belong to the dye families known as rhodamines, fluoresceins, coumarins, naphthalimides, benzoxanthenes and acridines. Typical dyes include Basic Red 1, Basic Violet 10, Basic Violet 11, Basic Violet 16, Basic Yellow 40, Solvent Yellow 44, Solvent Yellow 131 and Solvent Yellow 135. The fluorescent dyes comprise from about 0.5 to about 15% of the total weight of the pigment. 
     The pigment is formed by incorporating the fluorescent dye in the condensation resin during its formation and thereafter grinding the cooled resin to the proper particle size. The resin has been found to be friable and easily ground to the typical particle size of from about 10 to about 50 microns, the typical median particle size being 20 microns. This grinding is done in a conventional manner. 
     In addition to the foregoing components, the fluorescent compositions of the present invention may be modified by inclusion of other ingredients which may react with the diamine and diacid components. Typically, modifiers are included to increase the molecular weight by chain extension, alter the softening or melting point, provide enhanced compatibility for particular plastics to be colored, provide functional groups of special affinity for particular fluorescent dyes, impart thermal stability to fluorescent dyes or otherwise complement or enhance the suitability of the resin carrier composition for a particular application. Preferred modifiers include bi- and monofunctional acids, monofunctional amines, monofunctional alcohols, epoxies, glycols, metal oxides, metal carbonates and metal acetates. Examples of such modifiers include the following compounds. 
     Illustrative bifunctional acids include p-aminobenzoic acid, p-hydroxybenzoic acid, 2-chloro-4-hydroxybenzoic acid and salicyclic acid. 
     Illustrative monofunctional acids include p-tert-butylbenzoic acid, stearic acid, lauric acid, pelargonic acid, palmitic acid, and cyclohexanecarboxylic acid. 
     Illustrative monofunctional amines include n-nonylamine, isononylamine, stearylamine, cyclohexylamine and benzylamine. 
     Illustrative monofunctional alcohols include stearyl alcohol, cetyl alcohol, n-nonyl alcohol, benzyl alcohol, monofunctional aliphatic alcohols having a weight-average molecular weight in the range of from 400 to 700, n-decyl alcohol, tridecyl alcohol, cyclohexanol, 2-ethylhexanol and cyclododecanol. 
     Illustrative epoxies include bisphenol A epoxies and aliphatic epoxies. 
     Illustrative glycols include cyclohexane dimethanol and ethylene glycol. 
     Illustrative metal oxides, metal carbonates and metal acetates include zinc oxide, zinc carbonate, antimony triacetate, antimony pentoxide, antimony trioxide, calcium oxide, calcium carbonate, calcium hydroxide, magnesium oxide and magnesium carbonate. 
     The amount of modifier used should not adversely affect the basic novel properties of the fluorescent compositions. Usually, the amount of the reactive modifier will range from about 1 to about 10% based on the total weight of the composition. 
     Conventional additives such as opacifiers, antioxidants and processing acids may also be added to the fluorescent pigments. These materials may be added prior to, during, or after the condensation reaction is completed. 
     The fluorescent compositions or pigments of the present invention provide improved plateout characteristics as compared with the modification of the polyamides of the &#39;884 patent, supra. These improvements have been observed in subsequent molding techniques including blow molding and injection molding. Further, the fluorescent compositions have good friability characteristics and may be readily ground to desired pigment particle sizes. It has also been found that pellets containing increased amounts of fluorescent composition or pigment may be prepared for use in plastics processing. In accordance with the invention, pellets containing more than 30% and up to 50% pigment by weight have been prepared. This reduces the amount of carrier resin and more efficiently colors the plastic. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The compositions of the present invention are prepared by condensation polymerization reactions illustrated by the following examples. In the examples and throughout the specification all parts and percentages are by weight unless otherwise indicated. 
     EXAMPLE 1 
     A reaction vessel equipped with an agitator and oil heating means was preheated by circulation of 160° C. heating oil. The preheated reactor was then charged with 1,243 parts of 2-methylpentamethylenediamine and 7 parts of zinc oxide. To the blended and heated components, 1,355 parts of isophthalic acid was added with further heating by increasing the heating oil temperature to about 270° C. Thereafter, the heating oil temperature is controlled to provide a batch temperature of about 240° C. for sixty minutes. 200 parts of stearyl alcohol was then added and a batch temperature of 240° C. was maintained for 15 additional minutes. A strong red pigment is produced by adding a combination of dyes, namely, Solvent Yellow 135, Basic Violet 11:1 and Basic Red 1. A total of 176 parts of dye were added. 
     EXAMPLE 2 
     A reaction vessel equipped as in Example 1 was charged with 1,042 parts of 1-amino-3-aminomethyl-3,5,5-trimethyl cyclohexane, commonly known as isophorone diamine, and 200 parts water. To the blended and heated components 574 parts of azelaic acid and 607 parts of isophthalic acid were added with further heating by increasing the oil temperature to 300° C. Thereafter, the oil temperature was controlled to provide a batch temperature of about 245° C. A strong red pigment is provided by adding a combination of dyes, namely, Solvent Yellow 160, Basic Violet 11:1 and Basic Red 1. A total of 252 parts of dye were added. 
     The diamine and diacid components as well as any reactive modifiers continue to react and increase the molecular weight of the resulting fluorescent pigment as the batch is held at an elevated temperature, e.g. 245° C. in Example 2. For evaluation of molecular weight variation, pigment samples were withdrawn at about 10 minute intervals. The weight-average molecular weights of the samples were measured using conventional gel permeation chromatography techniques. The drawing shows a graph having the &#34;hold time&#34; at 245° C. plotted along the abscissa and the molecular weight plotted along the ordinate. As indicated, the molecular weight increased from an initial value of about 7,000 to about 18,000 after 50 minutes. The rate of increase in molecular weight is proportional to the batch temperature. It should also be appreciated that pigments having satisfactory colorant characteristics and molecular weights as low as 3,000 may be provided in accordance with the invention by preselection of the diamine, diacid and modifier components and the use of reaction procedures of shorter duration and/or lower temperature. 
     In the following Table I, additional illustrative examples showing the use of various diamines, diacids, modifiers and fluorescent dyes are reported. Each of the examples was prepared in accordance with Example I. 
     
                                           TABLE I__________________________________________________________________________                      DyeEx.   Diamine  Diacid  Modifier     TotalNo.   Type Parts       Type           Parts               Type Parts                       Type Parts__________________________________________________________________________ 3 HMDA 166 IPA  91         SY 131                            9       AZA 103 4 1,2DCH   124 IPA 148 SA   65 SY 135                            6                       BV 11:1                       BR 1 5 1,4DCH    23 IPA 200         SY 160                            4   2,MPD    93 6 2,MPD   116 IPA 159         SY 135                            4       PHT  36 7 2,MPD   166 IPA 166 ZnO  10 BV 11:1                            3       ADA  34         BR 1 8 2,MPD   161 IPA 174 ZnO   1 SY 135                              8.3       AZA  65         BV 11:1                       BR 1 9 2,MPD   116 IPA 125 ZnO   1 SY 135                            7       DDA  5810 2,MPD   125 IPA  83 SA   11 AY 239                            11       DAGS            66 BA   1311 2,MPD   116 DMT 195 U550  2 SY 135                            412 2,MPD   138 IPA 177 ZnO   1 SY 160                            21               U550  4 BV 16               PABA 15 BR 113 2,MPD   116 IPA 149 PHBA 28 SY 135                            314 2,MPD   116 IPA 200 BAM  22 SY 135                              1.9                       BV 11:1                       BR 115 2,MPD   128 IPA 193 ZnO   1 BV 16                            17               U425  5 BR 116 2,MPD   116 IPA 166 CHDM 80 SY 135                            8               BA   24 BV 11:1               1,4ET                    11 BR 1 217 2,MPD   104 IPA 175 CHDM 16 SY 135                            318 2,MPD   211 IPA 423 PE   34 SY 160                            13               CHA  76 BV 11               ZCO  25 BR 1               HPO   119 2,MPD   166 IPA 175 U550  4 SY 135                            18               AT    2 BV 11:1                       BR 120 2,MPD   127 IPA 164 SUA  22 SY 135                            7                       BV 11:1                       BR 121 2,MPD   104 IPA 172 PE   12 SY 135                            7               PHT  24 BV 11:1                       BR 122 2,MPD    95 IPA 170 IA   65 SY 135                            7                       BV 11:1                       BR 1__________________________________________________________________________ HMDA Hexamethylenediamine 2,MPD 2,Methylpentamethylenediamine 1,2DCH 1,2Diaminocyclohexane 1,4DCH 1,4Diaminocyclohexane PHT Phthalic acid/Phthalic anhydride IPA Isophthalic acid SUA Succinic acid/Succinic anhydride ADA Adipic acid DDA Dodecanedioic acid DAGS Mixture of succinic/glutaric/adipic (30/40/30) DMT Dimethyl terephthalate PABA pAminobenzoic acid PHBA pHydroxybenzoic acid AZA Azelaic acid SY 135 Solvent Yellow 135 BV 11:1 Basic Violet 11:1 BA Benzoic acid BAM Benzylamine SA Stearic acid CHDM Cyclohexane dimethanol PE Pentaerythritol HPO Phosphorous acid AT Antimony triacetate IA Isononylamine U425 Monofunctional aliphatic alcoholave. mol. wgt. 425 U550 Monofunctional aliphatic alcoholave. mol. wgt. 550 ZCO Zinc carbonate 1,4ET 1,4 Butenediol diglycidol ether CHA Cyclohexylamine BR 1 Basic Red 1 
    
     The plateout of various molecular weight pigments made in accordance with Example 2 was evaluated using a test procedure wherein a blow molding machine is used to blow mold a fixed weight amount of a resin colored with the fluorescent pigment to be evaluated. The total weight of the plateout or organic species deposited on a blow pin insert due to the blow molding is considered to indicate the plateout characteristics of the fluorescent pigment. 
     A Rocheleau blow molding machine, Model SPB-2, is used in the test procedure. The blow pin is modified to include a removable stainless steel insert on which plateout is collected. The amount of plateout is determined by weighting the insert before and after the blow molding of the resin. 
     The fluorescent pigment to be tested is dry blended in a formulation including 20% fluorescent pigment, 6% titanium dioxide and 74% low density polyethylene having a melt index of 8.0. The blend is converted into a masterbatch or color concentrate by extrusion through a Killion 11/4 inch plastic extruder at a temperature of about 420° F. The dried extruded strands of resin have about a 1/8 inch diameter and they are chopped to a length of about 3/16 of an inch. Of course, the pellets may be of any size conventionally used in coloration during plastic processing. The pellets may be formed by any conventional technique and in any shape including hot roll processing to sheet form and subsequent comminution of the sheet to provide rectangular-shaped pellets. The fluorescent pigment is believed to be dispersed in a continuous phase of polyethylene in the pellets due to the melt blending of the pigment and the plastic. 
     The pelletized concentrate is letdown in a ratio of 1:10 in blow molding grade high density polyethylene having a melt index of 0.3. After cleaning, weighing and reinstalling the blow pin insert, a 20 pound test quantity of the mixture is blow molded to produce about 100 bottles of a selected bottle configuration. After the blow molding is completed, the blow pin insert is weighed to determine the amount of plateout. 
     Referring to the drawing, the blow pin plateout weight in milligrams is indicated on the ordinate of the graph for the pigment samples of Example 2 taken at 10 minute intervals. As shown by the data points, relatively higher amounts of plateout occur for fluorescent pigments having molecular weights less than about 9,000. The amount of plateout slightly decreases as the molecular weight increases to 18,000. 
     The fluorescent pigment of Example 1 was also prepared for injection molding plateout tests by letdown in a ratio of 1:20 in the same blow molding grade high density polyethylene as used for the above blow molding plateout test. A 75 ton Newbury injection molding machine, Model H4 75RS is used in this test to mold a three-step color chip of generally rectangular shape and about 21/4&#34;×4&#34;. Beginning with a clean mold, 3,000 grams of the letdown mixture is molded into about 275 color chip samples. 
     After molding of the color chips is completed, the percentage area of the face mold covered by plateout is determined for each of the three steps. The intensity of the plateout as indicated by the thickness thereof is subjectively estimated for each step using a scale of 0 to 10 with zero indicating no plateout. These three area percentages are averaged to determine a single number evaluation of 0 to 10 for injection molding plateout. The results are reported in Table II below. 
     Comparative pigment Example A having a polyamide resin carrier was prepared in accordance with Example 23 of U.S. Pat. No. 3,915,884. The polyamide pigment had the following formulation. 
     
         ______________________________________COMPONENT     PARTS______________________________________Cyclohexylamine         239Isophorone diamine         206Isophthalic acid         400Zinc oxide     77Adipic acid   176Water          34Solvent Yellow 131          49Basic Violet 11:1          13Basic Red 1    10______________________________________ 
    
     Comparative pigment A contained about 20% cyclohexylamine by weight as indicated and it had a molecular weight of less than 2,500. 
     Comparative pigment Example B was prepared by incorporating plateout reducing additives in the pigment of Example A. More particularly, silica and barium sulfate were each added in an amount equal to 0.6% by weight based on the resin to be molded. 
     The pigments of Example 1 and Comparative Examples A and B were each masterbatched, pelletized and tested for blow pin plateout and injection molding plateout as described above. The results are reported in Table II. 
     
                       TABLE II______________________________________       BLOW PIN   INJECTIONEXAMPLE     PLATEOUT   MOLDINGNO.         (mg)       EVALUATION NO.______________________________________1            5.8       2.50A           12.7       2.75B           10.2       2.70______________________________________ 
    
     Increasing amounts of fluorescent pigment were used to prepare masterbatches of pelletized color concentrates of each of the fluorescent pigments of Example 1 and Comparative Examples A and B. The pelletized color concentrates of the Comparative Examples A and B were limited to about 20 to 25% fluorescent pigment due to the inability to form uniform pellets at higher concentrations. At such higher concentrations, the processing of the melt blend of the Comparative Examples was more difficult due to the tendency of the extruded strand to break. Also, the pellets of the Comparative Examples tended to have irregular surfaces or cut edges characterized by fibrils. Such irregularly shaped pellets are undesirable to the molder since they interfere with the sizing and automatic processing of the pellets. In contrast, the pigment of Example 1 may be incorporated in pellets at higher concentrations ranging from about 30 to about 50% by weight without loss of pellet uniformity or the occurrence of fibrillation. Generally, the pigments of the invention may be used in pellets at concentrations which are 120% to more than 200% higher than those of the prior art pigments represented by Comparative Examples A and B. 
     It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.