JP2003519731A - Improved lubricant for web coating - Google Patents

Abstract

  (57) [Summary] An improved lubricant is provided for addition to a coating formulation for coating a moving web. The lubricant is in a blend comprising lecithin and at least one fatty ester. They may have up to 5% surfactant. The lubricant components are blended without the need to raise the temperature above 100 degrees F (38 degrees C). The fatty ester or fatty ester combination used is selected based on the effect that the fatty ester or fatty ester combination has on the high shear reaction of the mixture. These improved lubricant blends have improved storage stability, viscosity retention, coating uniformity and structure retention. They not only provide improved performance to related prior art compositions, but also provide improved anti-exudation, high shear, and rheological properties. As a result, coatings comprising the lubricant blends of the present invention have improved appearance, durability, and printability.

Description

Detailed Description of the Invention

TECHNICAL FIELD This invention relates to improved lubricants for coating moving webs. It is especially important that these lubricants have improved performance in high speed applications without causing significant viscosity changes.

BACKGROUND Paper and paperboard webs are often coated to improve properties such as printability and appearance. The coating mixture used is applied at high speed to the moving web in the coating apparatus. Typically, these coating mixtures include pigments, adhesive binders, and other additives that improve or modify coating properties and related properties. Pigments used include, among others, kaolin and other clays, titanium dioxide, calcium carbonate or silicates, zinc oxide, talc, diatomaceous earth, synthetic polymers, and aluminum powder. Styrene butadiene latex, starch, and polyvinyl acetate are some of the binders that can be used. If the coating composition has insufficient stability under processing and / or storage conditions, the color distribution will be non-uniform and undesirable. This can result from both changes in the concentration distribution of the pigment used and changes in the coating layer thickness.

Shear forces and other chemical phenomena and physical forces can cause adverse effects such as in coating mixtures and coatings as they are applied to moving webs in their viscosity, integrity and uniformity. This can lead to costly problems both in the coating application method and in the finish and quality of the coated paper products, which problems are known to manufacturers of coated paper products.

As the speed of the web moving through the coating equipment is increased, shear forces are increased for the coating mixture applied to the web. This increase in shear force can compound the existing problems of process and paper quality. Problems with increased speed include viscosity adjustment, weeping, calcification, streaks, whiskering, and generally poor performance (or "workability") problems. Improved uniformity of the coating mixture at these high shear levels is important to avoid poor quality coated sheets resulting from these problems.

Typical additives for improving the performance, overall integrity, and uniformity of coatings and coating mixtures are lubricant additives such as calcium stearate dispersions and polyethylene emulsions. These lubricant additives in the coating mixture act primarily to increase the smoothness of the coating. However, there are many other effects from these lubricants known to occur, such as rheological properties, plasticity, smoothness, coating gloss, antidusting, and print quality.
Not all of these effects are desirable. Therefore, it would be advantageous to reduce the number of different additives to a coating mixture without compromising the benefits of a given composition as much as possible.

Orthoefer in US Pat. No. 4,200,551 describes the use of a blend of crude lecithin and a surfactant to produce a concentrated water dispersible lecithin additive. The surfactant is a polyoxyalkylene monoglyceride or diglyceride, a polyoxyalkylene derivative of a partial fatty acid ester and hexitol anhydride, or a combination thereof. The preparation of these blends is carried out at elevated temperatures of 40-212 ° F (40-100 ° C). These '551 patent additives with improved dispersibility in water are disclosed to be particularly suitable for the food industry.

[0007] Kronstein et al. In US Pat. Nos. 4,520,153, 4,056,494 and 4,126,591 provide paint compositions to obtain a uniform pigment concentration in the subject coating after mixing even after extended storage. The use of lecithin and lecithin derivatives for the modification of pigments in articles is disclosed. Maintaining a uniform coloration is especially important to the authors when more than one pigment is used. The former two patents disclose direct application to as little as 0.5% (based on the amount of pigment) of solid pigment particles in a liquid mixture for improved stability and uniformity. . The '153 patent is also interested in providing non-corrosive paints. Waxes may be used with lecithin, but the use of fatty acid esters is not taught or required. The '591 patent further discloses that the use of at least 4% lecithin in the paint coating composition provides similar improvement. For aqueous coatings, the use of lactic acid or its esters or alkyl esters of propylene glycol or condensed ethylene glycol is taught.
However, these dispersants have been specified for use with the modified lecithins disclosed as required for aqueous systems. No use is suggested for high speed web coating.

US Pat. No. 5,277,992 (Sinohara et al.) Teaches the use of two slip agents in coatings for heat transfer ink sheets. One type of slip agent used may be lecithin and / or higher fatty acid alkyl esters. However,
The second slip agent is taught to be selected from polyoxyalkylene alkyl (or aryl) phosphates.

[0009] Nikoloff et al. In US Pat. No. 4,766,015 disclose fatty acids (vehicles), surfactants (
An attempt was made to tackle the problem of high speed paper coating with an emulsifier) and an additive mixture of crude lecithin components. Surfactants are required in these mixtures so that they are sufficiently dispersible and lubricious to function as paper coatings. Further, it is stated that surfactants are needed to keep the lubricant in the coating formulation. This is because lecithin is not water dispersible. If desired, these mixtures may also contain plasticizers such as fatty esters. The examples describe the preparation of these mixtures requiring stirring with heating at 120 ° F (49 ° C). However,
These mixtures do not work well with modern and high speed coating methods, such as with modern high speed printing equipment, having speeds greater than 6000 fpm and even greater than the speeds intended for use with the coating mixture of the '015 patent. .

Nikoloff attempts to address these problems in US Pat. No. 5,858,933 with an additive mixture of chemically modified lecithin and a (C8-20) fatty ester. Preferred esters are methyl esters, butylene glycol esters, ethylene glycol esters, pentaerythritol esters, polyethylene glycol esters, polypropylene glycol esters, sorbitol esters, and trimethylolethane esters. The chemical modification of lecithin is said to act as a self-emulsifying agent, thereby allowing the omission of surfactant from the mixture. The preparation of stable clay coatings and prints at very high speeds in modern coating and printing equipment is a special focus of the '933. Like '015, the' 933 mixture is prepared under stirring with heating at about 130 ° F (54 ° C).

Similarly, Mizobuti et al. In US Pat. No. 5,196,080 uses lecithin and / or fatty acid esters as release agents, emulsifiers, and surfactants in roll coatings, gravure coatings, and hot melt coatings. Is described. The coating mixture is melted,
Or they are kneaded at 120 ° C. The authors do not teach the use of unmodified lecithin with fatty acid esters as being of particular benefit.

Williams et al. In US Pat. No. 5,284,690 disclose the use of modified and / or unmodified lecithin in aqueous release coating compositions. Lecithin is in a mixture with water soluble polymers and / or latex polymers. These polymers are said to be nonionically stabilized. One group of possible stabilizers includes ethylene oxide derivatives of long chain fatty acids. It is stated that the release coating is scrape coated and can be applied by knife coating, roll coating or print coating. All the examples shown contain less than 44% solids. It is not suggested or taught that the use of both lecithin and fatty acid esters in the coating mixture is beneficial over using lecithin alone.

DISCLOSURE OF THE INVENTION The present invention involves the addition of surfactants or chemical modification of lecithin to produce coating mixtures with improved high stability in the very high shear rates of modern coating and printing equipment. It relates to an improved lubricant additive mixture which does not require. This high stability is maintained even at high solids. Surfactants and other additives frequently have many effects on lubricant mixtures. Sometimes some of these effects are undesirable. Therefore, it is preferable to have a lubricant mixture that contains as few components as possible to obtain the best results that are not complicated by the undesired side effects of other additives. In particular, the mixtures according to the invention do not require ethanolamine or dipropylene glycol as additives. Further, the preparation of these inventive mixtures can be accomplished by at least 104 ° F. (as disclosed in the '551,' 080, '933, and' 015 patents.
No heating to 40 ° C is required. The ingredients are gradually blended directly until the blend is completely uniform. In addition, storage stability is improved over related prior art additives such as those described in the '015 patent.

Unlike the '015 mixture, which includes fatty acids as the mixture vehicle, the inventive mixture described herein is not. In the mixtures according to the invention, fatty esters are combined with unmodified lecithin, unlike the required combination with the modified lecithins of the '591 and' 933 patents. It has been found that the High shear reaction level can be adjusted by the choice of fatty ester for use.

Therefore, the improved lubricants of the present invention provide a uniform coating structure with improved rheology when applied to the web in a very fast manner, especially with respect to viscosity response. The resulting coating has excellent uniformity, fluidity, and whiteness.

Further, the improved lubricants of the present invention have a non-uniform color appearance, component transfer or bleed,
It provides a stable coating structure that effectively reduces or minimizes problems such as streaking, dusting, whiskering, blade scratching, and oozing. Not only are these lubricants more stable than related prior art lubricants conventionally used in coating processes, but they are more stable during storage than related prior art lubricant mixtures.

Furthermore, the improved lubricants for coating moving webs of the present invention maintain a uniform and stable coating structure even under varying pressure and physical forces found during the coating process. In other words, they are more resistant to the adverse effects of high shear, maintaining stable viscosities within the desired range despite high shear forces.

BEST MODE FOR CARRYING OUT THE INVENTION Lecithin is a naturally occurring mixture of phospholipids found in animal and plant cells. The lecithin mixture depends on the source and includes phosphatidylcholine, phosphatidylinositol, and phosphatidylethanolamine. The chemically described lecithin is glycerol reacted with two fatty acids and a phosphoric acid with an amino group reacted with residual hydroxyl.

As noted above, lecithin and its derivatives are preferred lubricants for use in the paper coating industry, especially for moving web applications. These lubricants may be coated directly onto the solid pigment, mixed into the coating formulation for subsequent application to the web, or applied separately from the coating formulation, such as by spraying onto the web. May be.
However, given the limitations of prior art lubricant mixtures and the constant improvement in equipment speed, new and improved lubricants are constantly being sought.

The lecithin used with the mixture of the present invention is unmodified. It may be from plant and / or animal sources. In addition, selected lecithin substances, such as phosphatidyl choline or phosphatidyl cephalin, may be used alone.

Fatty acid esters for use include linear and branched alkyl esters of (C5-C22) fatty acids as well as alkylene glycol esters and diesters. They may be used in combination with one another and optionally substituted with (poly) oxyalkylene groups and / or other naturally acting substituents. The fatty moieties in the diester may be the same or different. Typical fatty acid esters that may be used in the mixture of the present invention include methyl oleate, propylene glycol dioleate, butyl stearate, isopropyl myristate, ethyl oleate, octyldodecyl myristate, long chain fatty acids such as stearin. Acid, lauric acid, capric acid, oleic acid, myristic acid, palmitic acid, and caproic acid ethylene oxide and propylene oxide derivatives, sorbitan monostearate, pentaerythritol oleate, ethylene glycol, butylene glycol or propylene glycol alkyl ester And mixed alkyl esters and diesters, tall oil or red oil alkyl esters, and combinations thereof.

The present invention provides an improvement in lecithin lubricant mixtures by preparing lecithin blends with fatty esters without the need for elevated temperatures during the blending process. A clear stable blend is obtained without the use of further additives to prevent haze or precipitation. The response of the blend to high shear can be controlled by the choice of fatty ester for use. For example, the use of methyl oleate stabilizes the lubricant mixture against viscosity shifts under high shear. Other fatty esters and combinations of fatty esters can increase or decrease the stable high shear viscosity of the lubricant mixture.

Generally, the mixture of the present invention comprises 50-85% lecithin, 15-50% fatty ester, and
Contains 0-5% surfactant. Examples of this surfactant (whether used alone or in mixture) are conventional anionic agents such as alkali metal salts of fatty acids, alkyl sulphates, alkyl sulphonates, alkylaryl sulphonates, sulphosuccinates. , Alkyl phosphates, abietic acid salts (whether hydrogenated or unhydrogenated), nonionic agents such as polyethoxylated fatty alcohols, polyethoxylated alkylphenols optionally polysulfated, and polyethoxylated fatty acids Etc.

Pigments may be used with these lubricant mixtures. Preferred pigments for use include calcium carbonate, titanium dioxide, precipitated calcium carbonate, delaminating clay, calcined clay, aluminum trihydrate, and combinations thereof. However, other pigments known in the art may be used with the lubricant mixtures of this invention.

In the present manufacturing method, the components of the lubricant mixture are mixed at low speed in the reactor with blades to prevent the introduction of large volumes of air. If this mixing becomes labor intensive, then slight heating can be applied just enough to reduce the viscosity sufficiently to allow labor-free mixing.

Adhesion of coated particles in the blade coater or excessive degradation of the coating structure can result in leaching during the coating process. To evaluate the anti-leaching properties of this product mixture, the product to be tested is included in the sample coating formulation with 1.5 wet parts of pigment per 100 parts. This initial test formulation contains diglycerides. This initial test coating formulation is then left for 2-4 hours to determine if the diglyceride begins to separate.

If this initial test is passed without causing diglyceride separation, the coating formulation of the tested product without diglyceride is tested for viscosity response by Brookfield viscosity evaluation. A significant change in viscosity, either upwards or downwards, is considered a negative effect.

If the tested product does not show a negative effect in the viscosity response test, it is subsequently tested for high shear and rheological effects using a Hercules high shear viscometer. First, a significant shift in the high shear viscosity of the coating is sought.
If they are absent, a slight shift is sought. Depending on the intended application, some slight shift may be acceptable at high shear viscosities of the coating.

EXAMPLES Example 1 A first charge of 800 lbs (363 kg) of lecithin is charged to a bladed reactor at low mixing speed. A second charge of 200 lbs (91 kg) of methyl oleate is then slowly mixed with lecithin until there is no separation of the two liquids. The resulting product was stable after one day of storage and provided resistance to high shear viscosity changes when added to coating formulations tested on a Hercules high shear viscometer.

Example 2 A charge of 830 lbs (377 kg) of lecithin is initially charged at low speed into a bladed reactor. A charge of 150 pounds (68 kg) of propylene glycol dioleate is then mixed until the blend is uniform. Finally, Targitor Np-9 20 lb (9.1
(kg) charge until the product is completely homogeneous. The resulting product was stable after one day of storage with an increase in stable high shear viscosity.

Comparative Example 1 Lecithin, red oil, and Tridet 2692A (12: 5: 3) were mixed until uniform.
Mixed under stirring at 20 ° F. (49 ° C.) (according to the method of the '015 patent). The product was cloudy and formed a brown precipitate after 1 day of storage.

COMPARATIVE EXAMPLE 2 The same combination of components used in the first comparative example was likewise mixed in a ratio of 21: 14: 5. Similar results to the first comparative example were obtained.

Comparative Example 3 A mixture similar to Comparative Examples 1 and 2 was prepared in a similar manner by the addition of triethanolamine and dipropylene glycol. The product was clear and very stable and showed no precipitation after 1 day of storage.

The embodiments of the invention and the claims below are examples of novel features of the invention. Various changes and modifications of the preferred embodiment will be apparent to those skilled in the art. It is to be understood that such changes and modifications are within the scope of the invention as defined by the claims, unless they depart from the claims.

─────────────────────────────────────────────────── ─── Continued front page    (81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE, TR), OA (BF , BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, G M, KE, LS, MW, MZ, SD, SL, SZ, TZ , UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, B Z, CA, CH, CN, CR, CU, CZ, DE, DK , DM, DZ, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, J P, KE, KG, KP, KR, KZ, LC, LK, LR , LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ, NO, NZ, PL, PT, R O, RU, SD, SE, SG, SI, SK, SL, TJ , TM, TR, TT, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW

Claims (20)

[Claims] 1. An improved lubricant additive mixture suitable for combination with an aqueous paper or paperboard coating mixture, said lubricant additive mixture comprising: (a) 50-85% by weight of lecithin; ) 15-50% by weight of at least one fatty ester, each of said at least one fatty ester having a corresponding high shear reaction, and (c) comprising 0-5% by weight of surfactant. An improved lubricant additive mixture characterized in that: 2. An improved lubricant additive mixture suitable for combination with an aqueous paper or paperboard coating mixture, said lubricant additive mixture comprising: (a) 50-85% by weight of lecithin, (b) ) 15-50% by weight of at least one fatty ester, each of said at least one fatty ester having a corresponding high shear reaction, and (c) comprising 0-5% by weight of a surfactant. Characterized in that the mixture is blended without any increase in temperature other than slight heating when required to reduce the viscosity of the mixture just enough to allow effortless movement of the mixing blades. Improved lubricant additive mixture. 3. The lubricant additive mixture of claim 1, wherein the at least one fatty ester is selected from the group of propylene glycol dioleate, dipropylene glycol dioleate, methyl oleate and combinations thereof. . 4. The lubricant additive mixture of claim 2 wherein said at least one fatty ester is selected from the group of propylene glycol dioleate, dipropylene glycol dioleate, methyl oleate and combinations thereof. . 5. A lubricant additive mixture as claimed in claim 1 which comprises 80% lecithin and 20% methyl oleate. 6. A lubricant additive mixture as claimed in claim 2 which comprises 80% lecithin and 20% methyl oleate. 7. A composition comprising 83% lecithin and 15% propylene glycol dioleate, further comprising 2% emulsifier, said emulsifier being selected from the group of Tagitol Np-9, other emulsifiers and combinations thereof. A lubricant additive mixture as claimed in claim 2. 8. A composition comprising 83% lecithin and 15% propylene glycol dioleate, further comprising 2% emulsifier, said emulsifier being selected from the group of Tagitol Np-9, other emulsifiers and combinations thereof. A lubricant additive mixture as claimed in claim 1. 9. A method of preparing a lubricant additive mixture comprising lecithin and at least one fatty ester, said method comprising: treating said lecithin and said at least one fatty ester at a temperature of 40 ° C. (104 ° F.) or higher. A method for preparing a lubricant additive mixture, comprising the step of blending without increasing the temperature. 10. A further step of blending in a reactor having at least two speed settings, one of said settings being a low setting, using at least one blade, wherein the speed of said at least one blade is said 10. A method according to claim 9 which is kept at a low setting. 11. Just enough to allow the labor-free movement of the at least one blade to occur without increasing the temperature other than slight heating when the blending is required and to increase the viscosity of the mixture. 11. The method according to claim 10, wherein 12. (a) First adding the lecithin to the reactor, (b) starting a mixing mechanism prior to the addition of the at least one fatty acid, and (c)
The method of claim 9 further comprising secondly adding the at least one fatty ester to the reactor. 13. (a) First adding the lecithin to the reactor, (b) starting a mixing mechanism prior to the addition of the at least one fatty acid, and (c)
The method of claim 11 further comprising secondly adding the at least one fatty ester to the reactor. 14. A lubricant additive prepared by the method of claim 11. 15. A lubricant additive prepared by the method of claim 9. 16. The lubricant additive mixture of claim 1, wherein the at least one fatty ester is selected according to the high shear reaction desired for the mixture corresponding to the presence of the at least one fatty ester. . 17. A lubricant additive mixture according to claim 2 wherein said at least one fatty ester is selected according to the high shear reaction desired for said mixture corresponding to the presence of said at least one fatty ester. . 18. The lubricant additive of claim 15, wherein the at least one fatty ester is selected according to the high shear reaction desired in the mixture corresponding to the presence of the at least one fatty ester. 19. The lubricant additive mixture is a component of a web coating formulation comprising at least one pigment, wherein the at least one pigment is kaolin and other clays, titanium dioxide, calcium carbonate or calcium silicate, precipitated. A lubricant according to claim 1, which is selected from the group consisting of calcium carbonate, zinc oxide, talc, diatomaceous earth, delaminating clay, calcined clay, aluminum trihydrate, synthetic polymer, aluminum powder, and combinations thereof. Agent mixture. 20. The lubricant additive mixture is a component of a web coating formulation comprising at least one pigment, the at least one pigment being kaolin and other clays, titanium dioxide, calcium carbonate or calcium silicate, precipitated. A lubricant according to claim 2, which is selected from the group consisting of calcium carbonate, zinc oxide, talc, diatomaceous earth, delaminating clay, calcined clay, aluminum trihydrate, synthetic polymer, aluminum powder, and combinations thereof. Agent mixture.