JPH02265978A - Ink for heat-sensitive recording - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a thermal recording ink, and more particularly to a straw-sensitive thermal recording ink that allows partial printing and has excellent thermal responsiveness. I can buy things.

[Conventional technology]

Heat-sensitive recording materials generally contain a colorless dye precursor having a 1-child donating property, a color developer having a 1-child accepting property, and gold as a main component on a support. By heating with a heat head, hot pen, laser source, etc., the colorless dye precursor and color developer instantly react and a recorded image is obtained. -4160, Japanese Patent Publication No. 45-14039, etc.

Such heat-sensitive recording materials have the advantages of being able to record with a relatively simple device, being easy to maintain, and producing no noise, and are widely used in recording meters, facsimile machines, printers, computers, etc. It is used in a wide range of applications, including ticket terminals, labels, and automatic ticket vending machines.

These widely used heat-sensitive recording materials generally use paper as a base material and coat the entire surface of the base material with an aqueous heat-sensitive recording coating liquid, but in recent years, other heat-sensitive recording materials have been developed. Prepaid cards such as transportation cards, No. 1 Equality cards, and transportation cards for trains, buses, and taxis are on the rise. There is no need to coat the entire surface of the card, and it is often printed partially on a certain area of the card.

The heat-sensitive recording material using the above-mentioned electron-donating colorless dye precursor and single-child-accepting color developer has advantages such as good appearance, good feel, high color density, and % of the color hue. Absurd characteristics? On the other hand, when the heat-sensitive coloring part (recorded image part) comes into contact with plastics such as polyvinyl chloride, it may disappear due to plasticizers and additives contained in the plastic, or it may disappear due to chemicals contained in foods and cosmetics. It has the disadvantage that it has poor storage stability, such as easily disappearing when it comes into contact with other people, or easily fading due to short-term exposure to sunlight, and because of this disadvantage, there are certain restrictions on its use. This is the current situation, and its improvement is strongly desired.

As a heat-sensitive recording material in which two components react when heated and a recorded image with good storage stability is obtained, for example, Japanese Patent Application Publication No. 58-38733, Japanese Patent Application Laid-open No. 58-54085, Japanese Patent Application Publication No. 104959-1980, JP-A-58-149388, JP-A-59-115887, JP-A-1859-:11
No. 5888 and U.S. Pat. No. 4,521,793.
The specification discloses a heat-sensitive +18 record material whose two components are an imino compound and an isocyanate compound.

[Problems that the present invention attempts to solve]

Heat-sensitive recording materials made of isisoanate compounds and imino compounds have excellent storage stability of recorded images, so there are many references as mentioned above regarding the entire surface coating of paper substrates as an aqueous coating solution. There are many trends in partial printing using machines. For example, when partially printing aqueous blood, a longer drying process is required. In addition, paper and glass substrates have different surface suitability, and when coating a plastic base material with water-based coating, water-based blood has poor wettability with the base material and causes a repelling phenomenon, resulting in a uniform coating. It is not possible to apply a coating.

Thermal recording ink for this kind of partial printing is
゛An organic bath agent is used as a heating medium, and the present applicant has previously filed a patent application for a suitable binder in Japanese Patent Application No. 63-285080. There was room for higher sensitivity.

[Means for solving problems]

As a result of intensive research by the present inventors in order to obtain a highly sensitive thermal recording ink that is capable of partial printing and has excellent thermal responsiveness,
The aromatic isocyanate compound and the imino compound are respectively dispersed and/or dissolved in the organic bath agent and 7! By containing gallic acid and/or a derivative thereof as a sensitizer, the gold ink for thermal recording of the present invention could be obtained.

The sensitizers made of gallic acid and/or its derivatives according to the present invention include gallic acid, methyl gallate, ethyl gallate, propyl gallate, isoamyl gallate, octyl gallate, lauryl gallate, stearyl gallate, trimethoxy gallic acid, trimethoxy gallic acid methyl ester, gallic acid 3-methyl ether, gallic acid 3,
Examples include 4-dimethyl ether and gallic acid 3.5-dimethyl ether.

The above-mentioned sensitizer has a range of 1O to 50% when 100 parts by weight of the aromatic isocyanate compound and the imino compound are used.
0. It is added in an amount of 1 part, preferably 20 to 3002 parts, more preferably 30 to 200 parts. If the amount added is less than 10 parts by weight, the sluggishness will be poor, and if the amount exceeds 500 parts by weight, the color density will decrease as a result of dilution.

The organic solvent is an alcohol-based organic solvent or a hydrocarbon-based organic solvent, and the alcohol-based organic solvent is an aliphatic alcohol having 1 to 4 carbon atoms.

Examples of organic solvents include methanol, ethanol,
Examples include alcohol types such as N-70 vinyl alcohol, inpropyl alcohol, and butanol, ester types such as ethyl acetate and propyl acetate, and hydrocarbon types such as hexane and light oil.

The present invention will be explained in detail below. The thermosensitive recording ink of the present invention is intended to be capable of partial printing on a base material, particularly a plastic base material, such as a polyester sheet. A printing machine is suitable for partially printing only the necessary part of the base material, and a printing method that covers the entire circumference, such as a gravure printing machine, a flexible printing machine, and a screen printing machine, is suitable for the purpose of the present invention. These printing methods
- For boat fishing, it is necessary to use organic solvents that have low drying capacity and are easily volatile. However, water can also be used in combination within the range permitted by the drying capacity of the printing machine and the stability of the thermal recording ink.

In such a solvent-based heat-sensitive recording ink, the gallic acid or its derivative as a sensitizer according to the present invention may be monodispersed or co-dispersed with either an aromatic isocyanate compound or an imino compound as a color forming portion. By using this method, high sensitivity with excellent thermal response can be obtained.

The aromatic isocyanate compound used in the present invention is a colorless or flame-colored aromatic isocyanate compound or a heterocyclic isocyanate compound that is solid at room temperature, and for example, the following i 2m or more is used.

2.6-dichlorophenylisocyanate, p-chlorophenylisocyanate, 1.3-phenylene diinkane), 1.4-phenylene diisocyanate, 1
．． 3-dimethylbenzene-4,6-dicyaner),
1.4-dimethylbenzene-''2.5-diisocyanate, ], -methoxybenzene-44-diisocyanate, l-methoxybenzene-45-diisocyanate, 1
-ethoxybenzene-44-diisocyanate, a5-
dimethoxybenzene-1,4-diisocyanate, 2.
5-jethoxybenzene-1,4-diisocyanate,
2.5-dibutoxybenzene-1,4-diisoanate, azobenzene-4,4'-cyanurate, diphenyl ether-4,4'-diisocyanate, naphthalene 1
, 4-diisocyanate, naphthalene-1,5-diiso7anate, naphthalene-a6-diisocyanate, naphthalene-47-diisocyanate, 3,3'-dimethyl-biphenyl-4,4'-diisocyanate , 3.3
'-dimethoxybiphenyl-4゜41-diisocyanate, diphenylmethane-4゜4'-diisocyanate,
Diphenyl dimethyl meta 4,4'-diisocyanate, benzophenone + 3.3/-diisocyanate,
Fluorene-2,7-diisocyanate, anthraquinone-2,6-diisocyanate, 9-ethylcarbazole-3,6-diisocyanate, pyrene-3,8-diisocyanate, naphthalene-1,3, 7-) diisocyanate, biphenyl-2,4,4'-) diisocyanate, 4.4',4'-h diisocyanate 2,5-dimethoxytriphenylamine, p-dimethylaminophenyl isocyanate, Examples include tris(4-phenylisocyanate) thiophosphate. These isocyanate compounds may be used, if necessary, in the form of so-called blocked isocyanates, which are compounds with phenols, lactams, oximes, etc., and diisocyanate dimers, For example l-methylbenzene-44-
It may be used in the form of incyanurate, which is a diisocyanate dimer or a 3-isomer, or it can also be used as a polyisocyanate adducted with various polyols.

It is a colorless or light-colored compound that is solid at room temperature and is a compound that is easily absorbed by the imino compound used in the present invention (an aromatic compound residue that can form the general formula). A specific example is shown below. Depending on the purpose, it is also possible to use all two or more imino compounds in combination ◇3-Iminoisoindoline-1-
one, 3-imino-4,5,6,7-tetrachloroisoindolin-1-one, 3-imino-4,5,6,7-
Tetrabromoisoindolin-1-one, 3-imino-
4,5,6゜7-titrafluoroinindoline-1-
on, 3-imino-5,6-dichloroisoindoline-
1-one, 3-imino-4,5,7-)dichloro-6-methoxyindolin-1-one, 3-imino-4
, 5,7-trichloro-6-methylmerkabutoisoindolin-1-one, 3-imino-6-nitroisoindolin-1-one, 3-imino-isoindolin-1-one
Spiro-dioquinrane, 1゜1-dimethoxy-3-imino-isoindoline, 1.1-jethoxy-3-imino-4,5,6,7-titrachloroisoindoline, 1-
Ethoxy-3-imino-isoindoline, 1,3-diiminoindoline, 1,3-diimino-4,5,6,
7-titrachloroinindoline, 1,3-diimino-
6-Medoxyisoindoline, 1,3-diimino-6-
Cyanoisoindoline, 1,3-diimino-4,7-cythia 5.5.6.6-titrahydroisoindoline, 7-amino-&3-dimethyl-5-oxopyrrolo[3
゜4b) Pyrazine, 7-amino-43-diphenyl-5
-Oxopyrrolo[:3,4b) pyrazine, 1-inononaphthalic acid imide, 1-imino diphenic acid imide, 1-
Phenylimino-3-iminoindoline, 1-(3
'-chlorophenylimino)-3-iminoinindoline, "-(2' + 5'-dichlorophenylimino)-3-iminoinindoline, 1-(2', 4'
, 5'-1-lichlorophenylimino)-3-iminoisoindoline, 1-(2'-cyano-41-nitrophenylimino)-3-iminoisoindoline, 1-(2'-
Chloro-51-cyanoneenylimi/)-3-iminoisoindoline, 1-(2',6'-dichloro-41-
Nitrophenyl-3-iminoinoindoline, 1
-(2',5'-dimethoxyphenylimino)-3-
Iminoinindoline, 1-(2/I5/-jetoxyphenylimino)-3-iminoisoindoline, 1
-(2'-methyl-4'-nitrophenylimino)-3
-iminoisoindoline, 1-(5'-chloro-27-
fninoxyphenylimino)-3-iminoisoindoline, 1-(4'-N,N-dimethylaminophenylimino)-3-iminoindoline, 1-3'-NIN-
dimethylamino-4'-methoxyphenylimino)-3
-iminoisoindoline, 1-(2'-methoxy-5'
-N-phenylcarbamoylphenylimino)-3-iminoinindoline, X-(2'-chloro-51-trifluoromethylphenylimino)-3-iminoisoindo! i'%'l-(5'l6'-dichlorobenzothiazolyl-2'-imino)-3-iminoisoindoline, 1-(6'-methylbenzothiazolyl-21-imino)-3-imino Isoindoline, 1-(41-phenylaminophenylimino)-3-iminoindoline, 1-(p-phenylazophenylimino)-3-iminoindoline, l-(naphthyl-1'-imino)
-3-iminoisoindoline, 1-(anthraquinone-
1'-imino)-3-iminoisoi indolin, 1-(
5'-chloroanthraquinone-11-imino)-3-iminoisoindoline, 1-(N-ethylcarbazolyl-
3'-imino)-3-iminoisoindoline, 1-(naphthoquinone-11-imino)-3-iminoindoline, 1-(viridyl-4/-imino)-3-iminoisoindoline, 1-(benzimidase) lon-6/-imino)-3-iminoisoindoline, 1-(1'-methylanzimidazolone-6/-imino)-3-imino)-3-iminoisoindoline, 1-(7'- Chlorobenzimidacylon-5
t-imino)-3-iminoinindoline, 1-(benzimidazo9-2/-imino)-3-iminoisoindoline, 1-(benzimidazolyl-2'-imino)-
3-imino-4,5,6,7-titrachloroisoindoline, 1-(2/,4/-dinitrophenylhydrazone)-3-iminoisoindoline, 1-(benzzolyl-3'-imino)-3- iminoinindoline, 1-(benzzolyru-37-imino)-3-ino/
-4,5,6,7-titrabromoisoindoline, 1-
(benzzolyru-3'-imino)-3-imino-4,5
, 6,7-titrafluoroinoindoline, 1-(benzimidazolyl-2'-imino)-3-imino-4,7
-cythiatetrahydroisoindoline, 1-(4',5
'=dicyanoimidazolyl-2'-imino)-3-imino-5,6-dimethyl-4,7-biradiituindoline, 1-(cyanobenzoylmethylene)-3-iminoisoindoline, 1-(cyanocarbonamidomethylene) )−
3-iminoinindoline, 1-(cyanocarbomethoxymethylene)-3-iminoisoindoline, 1-(cyanocarboethquinmethylene)-3-iminoisoindoline, 1-(cyano-N-7 22-carbamoylmethylene) -3-iminoisoindoline, 1-[cyano-N-(
3'-Methyl7enyl)-rubamoylmetele7:l-
3-1minoindoline, 1-[cyano-N-(4'
-chlorophenyl)-carbamoylmethylene]-3-iminoisoindoline, 1-(cyano-N-(,4'-methquinphenyl)-carbamoylmethylene)-3-iminoisoindoline, 1-[cyano-N-( 3I-Chloro-4'-methylphenyl)-carbamoylmethylene, 3-iminoisoindoline, 1-(cyano-p-nitrophenylmethylene)-3-iminoisoindoline, l-
(dicyanomethylene)-3-iminoisoindoline, 1
-(cyano-1/, 2/, 4/-triazolyl-(3')-rubamoylmethylene)-3-iminoisoindoline, 1-(cyanothian°yl-(2')
) carbamoylmethylene)-3-iminoindoline, 1-(cyanobenzimidazolyl-(2')-carbamoylmethylene)-3-1minoisoindoline, 1-
(cyanobenzothiazolyl-(2')-carbamoylmethylene)-3-iminoinindoline, 1-C(cyanobenzimidazolyl-2')methylenecou 3-iminoisoindoline, 1-[(cyanobenzimidazolyl-2
/)-Methylene-3-imino-4,5,6,7-titrachloroisoindoline, 1-C(cyanobenzimidazolyl-2')-methylene-3-imino-5-methoxyisoindoline, 1-! : (cyanobenzimidazolyl-2')-methylenecy-3-imino-6-chloroisoindoline, 1-((1'-7enyl-3'-methyl-
5-oxo)-bi2zolidene-4']-3-iminoisoindoline, 1-[(cyanobenzimidazolyl-2'
)-methylene-3-imino-4, fushithiatetrahydroisoindoline, 1-C(cyanobenzimidazolyl-2')methylene-3-imino-5,6-dimethyl-4゜7-biradiituindoline, 1-[:( 1/-methyl-3'-n-butyl)barbyl-51]-3-
Iminoisoindoline, 3-Imino-1-sulfobenzoimide, 3-imino-1-sulfo-6-chlorobenzoimide, 3-imino-1-sulfo-5,6-dichlorobenzoimide, 3- imino-1-sulfo-4,5,6
,7-Chitrak C! μbenzoic acid imide, 3-imino-1
-Sulfo-4,5,6,7-tetrabromoan 1st aromatic imide, 3-imino-1-sulfo-4,5,6,7-tetrafluorobenzoin 1'1! imide, 3-imino-
1-Sulfo-6-methquine IRimide, 3-
Imino-1-sulfo-4゜5.7-)dichloro-6-methystalkagtobenzoimide, 3-imino-1-sulfonaphthoic acid imide, 3-imino-1-sulfo-5-bromonaphthoic acid imide, 3-imino- 2-methyl-4,
5,6゜7-tetrachloroisoindolin-l-one I
There is K.

The binder used as the thermal recording ink of the present invention is not limited in any way as long as it is compatible with an organic solvent, but the binders listed below are preferred, for example.

One of them is a imaginary combination of a monomer containing α, β ethylenically unsaturated carboxylic acid and one or more monomers selected from acrylic esters, methacrylic esters, and aromatic vinyls.

Examples of α, β ethylenically unsaturated carboxylic acid-containing monomers include acrylic acid, methacrylic acid, maleic acid,
Fumaric acid, itaconic acid, etc. are mentioned here.
It is good to include 0.15%, preferably 0.5 to 5ma1%, in order to impart total water resistance to the coating layer on the base material.

Examples of monomers of acrylic esters and methacrylic esters include 7-acrylates and methacrylates such as ethyl, propyl, butyl, hexyl, and 2-ethylhexyl.

Examples of aromatic vinyl compounds include styrene, vinyltoluene, halogenated styrene, and α-methylstyrene.

Furthermore, a polyvalent ethyleneimine compound or a polyvalent epoxy compound may be added to improve the water resistance.

In addition, 3 whose basic skeleton is inbutylene and maleic anhydride
Replaces copolymer with more than the original.

An example is imbutylene, maleic anhydride, and styrene.
Original copolymer, terpolymer of imbutylene, maleic anhydride, and methyl acrylate, terpolymer of imbutylene, maleic anhydride, and ethyl acrylate, terpolymer of imbutylene, maleic anhydride, and methyl methacrylate tertiary copolymer,
Tertiary copolymer of inbutylene, maleic anhydride, and ethyl methacrylate; Tertiary copolymer of inbutylene, maleic anhydride, and N-phenylmaleimide; Quaternary copolymer of isobutylene, maleic anhydride, styrene, and methyl acrylate Copolymer, quaternary copolymer of isobutylene, maleic anhydride, styrene, and ethyl acrylate, quaternary copolymer of imbutylene, maleic anhydride, styrene, and methyl methacrylate, isobutylene, maleic anhydride, styrene, and methacrylate , a quaternary copolymer of ethyl lylate.

Isobutylene and maleic anhydride #Rft can also be added to compounds* having polyfunctional hydroxyl groups, amino groups, epoxy groups, etc., in order to further increase the water resistance of the copolymer with three or more elements having the main skeleton. Specific examples of these compounds include 1,4-butanediol, ethylene glycol, chrycerin, 3-methyl-1,3,5-pentanetriol, ethanolamine, ethylenediamine, glycidyl methacrylate, and epoxy resin. The above binder is present in an amount of 5 to 50% by weight, preferably 10 to 3% by weight, based on the total solid content of the thermal recording ink.
If the amount added is less than 5% by weight, the adhesion and water resistance of the coating layer will be poor, and if it exceeds 50% by weight, the color density will decrease.

The /i6 thermal recording ink according to the present invention can contain other thermofusible substances in addition to the gallic acid and/or its derivatives according to the present invention in order to improve its thermal responsiveness. Those having a melting point of 60°C to 180°C are preferable, and those having a melting point of 80°C to 140°C are particularly preferable. For example, benzyl p-benzyloxybenzoate, stearamide, valmitic acid amide, N-methylolstearamide, β-s7tyl benzyl ether,
N-stearylurea, N,N'-distearylurea, phenylnisder β-naphthoate, 1-hydroxy-
2-naphthoic acid phenyl ester, β-naphthol (p
-methylbenzyl) ether, 1,4-dimethoxynaphthalene, l-methoxy-4-benzyloxynaphthalene, N-stearoylurea, 4-benzylbiphenyl,
1.2-di(.

-methylphenoxy)ethane, l-phenoxy-2-(
Examples thereof include 4-chlorophenoxy)ethane, 1,4-butanediol phenyl ether, and dimethyl terephthalate.

These thermofusible materials may be used alone or in combination.

In addition, the heat-sensitive recording ink contains pigments such as diatomaceous earth, Merck, kaolin, calcined kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum hydroxide, urine formalin resin, etc. ,
Higher fatty acid metal salts such as zinc stearate and calcium stearate, buff-in, polyethylene, paraffin oxide, etc. are used to prevent head wear and stickiness.
Waxes such as polyethylene, polyethylene oxide, stearamide, and castor wax, dispersants such as sodium dioctyl sulfosuccinate, ultraviolet absorbers such as benzophenone and benzotriazole, and surfactants, fluorescent dyes, etc. It can also be included.

Plastic base materials such as polyester sheets, polypropylene sheets, PVC sheets, and paper are mainly used as base materials, but various non-woven fabrics, laminates, synthetic sheets, metal sheets, and composite sheets made of combinations of these are also used depending on the purpose. can be used arbitrarily.

As printing machines for partial printing, gravure printing machines, 7-rekin printing machines, and screen printing machines are suitable for the purpose of the present invention, but letterpress printing machines,
An offset printing machine etc. can be used as appropriate.

In addition, in order to coat the entire surface of the base material, not only for partial printing,
There is no limit to the use of an air knife coater, roll coater, blade coater, etc. depending on the purpose.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 An imino compound and an aromatic isocyanate compound vlJ, which are color-forming components, were divided into liquids A and B as shown below, and mixed with a thermofusible substance in 1% polyvinyl alcohol (degree of saponification 30 to 40 mol%). )-isopropyl alcohol solution for 24 hours using a ball mill. Further, as cg, a molten g obtained by dissolving lauryl gallate of the present invention in inglovir aquol was used.

A'e, zinc nistearate 1% polyhinyl alcohol-isoglobil alcohol bath solution 75! IB@: p-pendyluoquine benzyl leftzoate 151
i 1% polyvinyl alcohol - isoglobil alcohol solution g, 75g Solution C: diuryl gallate (melting point 96°C) sop inglobil alcohol 150g A, Bg, cg dispersion g, t - After mixing, 1% polyvinyl alcohol -
Calcium carbonate 1 in isopropyl alcohol solution 459
5Ii'i dispersed 25% charcoal calcium dispersion was added and mixed well. Subsequently, 25% of acrylic acid ether-methyl methacrylate copolymer was added as a binder.
120"i of water was added and thoroughly mixed to prepare a heat-sensitive recording ink.

This heat-sensitive recording ink was coated on the entire circumference of a 125 μ thick polyester film using a gravure printing machine.
Partial printing was performed so that the printing rate was 4#/m'.

Comparison? l11 Lauryl gallate used in Example 1, Example 1
The recording sheet was made using the same method as above.

However, the effective coloring component was the same as in Example 1, and the fC coating was applied at a rate of 2.51 million yen/g.

Example 2 A recording sheet was obtained in the same manner as in Example 1 except that octyl gallate (melting point 75°C) was used instead of lauryl gallate used in Example 1. Example 3 A recording sheet was obtained in Example 1. Recording sheet 9 was prepared in the same manner as in Example 1 except that trimethoxy gallic acid methyl ester (melting point 83-84°C) was used instead of lauryl gallate.

Example 4 A recording sheet 'c was obtained in the same manner as in Example 1 except that gallic acid (225 to 250°C) and kumquats were used instead of lauryl gallate used in Example 1.

However, gallic acid was dispersed for 24 hours in a 1% polyvinyl alcohol-Improvil alcohol solution using a gold layer using a ball mill. The ratio recording sheets obtained in Evaluation Examples 1 to 4 and Comparative Example 1 used as the total c liquid were tested with an applied pulse width of 3 using a heat-sensitive 7mm tester (Matsushita Electronics Parts). .0 ms, applied voltage 16,25V
The optical density of the obtained image was measured using a Macben densitometer RD514. The results are shown in Table 1. 1 [Effects of the Invention] The thermal recording ink of the present invention allows partial printing on plastic substrates and enables high-sensitivity recording with excellent thermal responsiveness. . As a result, it can be effectively used as ink for the printing field and has extremely high industrial significance. It was possible to obtain a result with high optical density including IVC.

Claims (1)

[Scope of Claims] 1. A thermal recording ink containing an aromatic isocyanate compound and an imino compound as coloring components, wherein the aromatic isocyanate compound and the imino compound are respectively dispersed and/or dissolved in an organic solvent, A thermal recording ink characterized by containing gallic acid and/or a derivative thereof as a sensitizer. 2. The gallic acid and or its derivatives include gallic acid, methyl gallate, ethyl gallate, propyl gallate, isoamyl gallate, octyl gallate, lauryl gallate, stearyl gallate, trimethoxy gallic acid, trimethoxy methyl gallate. At least one selected from ester, gallic acid 3-methyl ether, gallic acid 3,4-dimethyl ether, and gallic acid 3,5-dimethyl ether
The heat-sensitive recording ink according to claim 1, which is a seed. 3. The thermal recording ink according to claim 1, wherein the organic solvent is an alcohol-based, ester-based, or hydrocarbon-based organic solvent. 4. The thermal recording ink according to claim 1, wherein the alcohol-based organic solvent is an aliphatic alcohol having 1 to 4 carbon atoms.